FOUS11 KWBC 042010
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 PM EST Thu Dec 4 2025

Valid 00Z Fri Dec 05 2025 - 00Z Mon Dec 08 2025


...Great Lakes...
Days 1-3...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes the next few
days. WPC probabilities continue to show low-to-moderate chances
(30-60%) for snowfall totals >4" each day Friday through Sunday,
primarily across eastern portions of the U.P. of Michigan as well
as northern parts of Michigan's Mitten. Slightly higher
probabilities for lower snowfall amounts exist downwind of Lake
Erie and Lake Ontario on Sunday.


...Mid-South to the Mid-Atlantic...
Day 1...

The first winter hazards of the season from the Mid-South to the
Mid-Atlantic continue tonight into Friday as a developing wave of
low pressure along the central Gulf Coast escorts a plume of Gulf
moisture northeastward into a frigid air-mass for early December.
Overrunning moisture along a narrow 925-850mb front from central AR
on east to the southern Appalachians is set to give rise to a
potentially disruptive wintry mix. Ice accumulations from the
Little Rock-Memphis-Nashville metro areas will be light, but given
it is the first icing setup of the season, untreated roads may
become slick and treacherous for travelers through the overnight
hours tonight.

As weak low pressure slides eastward along the Gulf Coast,
enhanced 290K isentropic ascent, increasing 850-700mb WAA aloft,
and strengthening frontogenesis will foster periods of snow to
develop from the central Appalachians and Blue Ridge of WV/VA on
east across the central/southern VA Piedmont tonight and into
Friday morning. Latest trends also suggest the northern extent of
the snow shield likely reaching into the Baltimore/Washington
Metros late tonight into early Friday morning. Similar to the Mid-
South, this will be the first accumulating snow of the season,
likely resulting in hazardous travel conditions on untreated
surfaces. Farther south, an icy overrunning setup looks to unfold
from the southern Appalachians on east across northern NC. A wintry
mix is likely to cause some minor ice accumulations on roads,
sidewalks, and vegetation Friday morning and could cause travel
delays.

WPC probabilities have increased with this forecast package, now
showing moderate to high chances (50-90%) for snowfall totals >2"
from the Central Appalachians to south-central VA, which does
include portions of the Richmond, VA metro area. Localized amounts
topping 4" are possible in the Blue Ridge Mountains of southwest VA
and southern WV. In terms of ice accumulations, most areas from
the Mid-South to the Mid-Atlantic can expect ice accumulations less
than a tenth of an inch, although some of the southern
Appalachians of NC could see localized amounts approach one-tenth.
The WSSI does depict localized areas of Minor Impacts through
Friday.


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track into the Northwest will usher in
copious amounts of Pacific moisture from the Pacific Northwest on
east into the Northern and Central Rockies. A steady barrage of

90th climatological percentile PWATs will stream across the

Pacific Northwest into the Great Basin and Rockies Friday into
Sunday. Synoptic-scale forcing will be present throughout the
Northern Rockies through Friday, then over the Central Rockies late
Friday into Saturday as a persistent NW-SE oriented 250mb jet
streak places its diffluent left exit region overhead. Snow levels
over the Pacific Northwest will dip as low as 3,000ft while the
Northern Rockies generally hover around 4,000ft. As height falls
ensue on Friday and continue Saturday into Sunday, snow levels will
drop to as low as 2,000ft, although the heaviest snowfall will be
confined to elevations above 5,000ft in the Bitterroots, Lewis
Range, and Sawtooth, above 6,000ft in the Tetons, Absaroka, Big
Horns, Bear River, and Wasatch Ranges, and above 7,000ft in the
central WY/CO Rockies.

Probabilities are impressive Day 1 and 2 across the higher terrain
from Glacier NP through Yellowstone NP including portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY, northern
Utah, and into the Park Range of CO. Here, WPC probabilities Day 1
and 2 reach above 70% for 8+ inches, and Day 1 and Day 2 snowfall
could be impressive above generally 6000 ft where locally 1-2 feet
is possible. Over the next few days, WPC probabilities paint a
wintry picture across many of the Northern and Central Rockies, as
well as the higher elevations of the Cascades (above 5,000ft) with
high chances (>70%) for snowfall totals >12" in all of these listed
ranges and elevations through Saturday. In fact, the higher
elevations of the Lewis Range, Bitterroots, and Tetons have
moderate-to-high chances (50-80%) for snowfall totals >24".
Moderate to heavy snow continues into Day 3, though probabilities
are less compared to Days 1 and 2. The WSSI shows many areas of
Minor Impacts of the Northern and Central Rockies, including some
Moderate to locally Major Impacts. The Major Impact potential areas (considerable disruptions; dangerous travel and widespread
closures) along the Wasatch east of Salt Lake City. Residents in
these mountain ranges should prepare for a multi-day stretch of
winter weather that results in difficult and treacherous travel
conditions.


...Midwest...
Days 2-3...

The active pattern of Pacific moisture and disturbances traversing
the Northwest will result in at least one of these disturbances
reaching the Midwest late Friday night into Saturday. A general
model consensus agrees a slug of rich Pacific moisture within the
700-300mb layer will advance across the northern Great Plains and
reach the Missouri River Valley by Saturday. While the latest
models still disagree somewhat on the strength and track of this
storm as it reaches the Central Plains on Saturday and then the
Upper Midwest Saturday night into Sunday, the synoptic-scale setup
should foster an 850mb low with sufficient 850-700mb FGEN to give
rise to a band of moderate-to-heavy snow. Right now, this appears
to be most likely from southeast South Dakota and northeast
Nebraska to southwest Minnesota and northwest Iowa.

The latest WPC probabilities have increased with this forecast,
now supporting 48-hour (Days 2-3) probabilities of 30-70% for
snowfall totals >4" for locations that banding (mentioned above) is
most likely. Additionally, 48-hour probabilities of >8", while low
(10-15%) are non-zero across southwest Minnesota and northwest
Iowa, suggesting that the favorable synoptic and mesoscale
processes at play could very much support a band of >6" snowfall
totals that cause travel headaches for residents in the Midwest.
Those in the Midwest should continue to monitor the forecast
closely as additional increases in probabilities are possible with
future forecast packages.


Miller/Mullinax





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 050815
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Fri Dec 5 2025

Valid 12Z Fri Dec 05 2025 - 12Z Mon Dec 08 2025


...Great Lakes...
Days 1-2...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes through Saturday.
Friday features modest WAA over the Great Lakes via SWrly flow that
looks to produce periods of snow over the northwestern towns of
Michigan's Mitten, while a cold frontal passage on Saturday
revitalizes LES bands over the Michigan U.P. and downwind of Lake
Ontario over the Tug Hill. WPC probabilities show low-to-moderate
chances (30-60%) for snowfall totals >4" over northwest mainland
Michigan today. By Saturday, most snowfall totals over the eastern
Michigan U.P. and downwind of Lake Ontario is likely to range
between 1-4".


...Mid-Atlantic...
Day 1...

The first winter hazards of the season for much of the Mid-
Atlantic is unfolding this morning. As weak low pressure slides
eastward over the Southeast, enhanced 290K isentropic ascent,
increasing 850-700mb WAA aloft, and strengthening low-level frontogenesis
is producing periods of snow from the central Appalachians and
Blue Ridge of WV/VA on east across the central/southern VA Piedmont
and across the DelMarVa Peninsula. Light snow is advancing as far
north as the Washington D.C./Baltimore metro areas, which is
may result in slick roads for the Friday AM commute. This will be
the first accumulating snow of the season, likely resulting in
hazardous travel conditions on untreated surfaces across much of
the Mid-Atlantic. Farther south, an icy overrunning setup looks to
unfold from the southern Appalachians on east across northern NC.
A wintry mix is likely to cause some minor ice accumulations on
roads, sidewalks, and vegetation Friday morning and could cause
travel delays. Snow should taper off by mid-afternoon with
lingering icy conditions across affected areas of the Mid-Atlantic
through Friday night.

Snowfall accumulations are likely to range between 1-4" from
southern WV and southwest VA across southern VA (including the
Richmond metro area) and into the lower DelMarVa Peninsula.
Localized totals >4" are possible in the Blue Ridge Mountains of
southwest VA. In terms of ice accumulations, most areas from the
VA/NC Blue Ridge on east across southern VA and northern NC can
expect minor accumulations less than a tenth of an inch, although
some of the southern Appalachians of NC could see localized amounts
approach one-tenth. The WSSI does depict Minor Impacts through
Friday afternoon for most areas referenced in this discussion with
some localized Moderate Impacts in the southern VA Piedmont.


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track into the Northwest will usher in
copious amounts of Pacific moisture from the Pacific Northwest on
east into the Northern and Central Rockies. A steady barrage of

90th climatological percentile PWATs will stream across the

Pacific Northwest into the Great Basin and Rockies today, with
another round of >90th percentile PWATs arriving in the Pacific
Northwest on Sunday. Synoptic-scale forcing will be located over
the Northern Rockies today, then over the Central Rockies Friday
night into Saturday as a persistent NW-SE oriented 250mb jet
streak places its diffluent left exit region overhead. Snow levels
over the Pacific Northwest will dip as low as 3,000ft while the
Northern Rockies generally hover around 4,000ft. As height falls
transpire today over the Northwest and continue through Saturday,
snow levels will drop to as low as 2,000ft, although the heaviest
snowfall will be confined to elevations above 5,000ft in the
Bitterroots, Lewis Range, and Sawtooth, above 6,000ft in the
Tetons, Absaroka, Big Horns, Bear River, and Wasatch Ranges, and
above 7,000ft in the central WY/CO Rockies. Snow looks to taper off
across the Central Rockies by Saturday evening, but the next
atmospheric river will deliver another plume of Pacific moisture
across the Pacific Northwest and northern Rockies on Sunday.

WPC probabilities are impressive Day 1 and 2 across the higher
terrain from Glacier NP through Yellowstone NP including portions
of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY,
northern Utah, and into the Park Range of CO. Here, WPC
probabilities Day 1 and 2 reach above 70% for 8+ inches, and Day 1
and Day 2 snowfall could be impressive above generally 6000 ft
where locally 1-2 feet is possible. Over the next few days, WPC
probabilities paint a wintry picture across many of the Northern
and Central Rockies, as well as the higher elevations of the
Cascades (above 5,000ft) with high chances (>70%) for additional snowfall totals >18" in all of these listed ranges and elevations through
Saturday. In fact, the higher elevations of the Lewis Range,
Bitterroots, and Tetons have moderate-to-high chances (50-80%) for
snowfall totals >24". Moderate to heavy snow continues into Day 3
over the WA Cascades and northern Rockies, though probabilities
suggest less snowfall compared to the more snowy stretches on
Friday and Saturday. The WSSI shows many areas of Minor and
Moderate Impacts across the Northern and Central Rockies,
including some locally Major Impacts. The Major Impact potential
areas (considerable disruptions; dangerous travel and widespread
closures) include areas along the Wasatch east of Salt Lake City
and the more remote areas of these Intermountain West ranges.
Residents in these mountain ranges should prepare for a multi-day
stretch of winter weather that results in difficult and treacherous
travel conditions.

...Northern Plains & Midwest...
Days 2-3...

The active pattern of Pacific moisture and disturbances traversing
the Northwest will result in at least one of these disturbances
reaching the Midwest late Friday night into Saturday. A slug of
rich Pacific moisture within the 700-300mb layer will advance
across the northern Great Plains and reach the Missouri River
Valley by Saturday. The synoptic-scale setup favors the development
of an 850mb low with sufficient 850-700mb FGEN and WAA to the north
and east of the 850mb low track to support a band of moderate-to-
heavy snow. The band of snow starts out Saturday morning across
the Dakotas, then heads for southern MN and northern IA by late
Saturday afternoon and evening, and begins to weaken in intensity
by early Sunday morning the snow reaches the Lower Great Lakes and
OH Valley.

The latest WPC probabilities have increased with this forecast,
now supporting probabilities of 50-70% for snowfall totals >4" for
locations that banding (mentioned above) is most likely across the
Midwest. However, given the favorable synoptic and mesoscale
processes at play, a band of >6" snowfall totals that cause travel
headaches for residents in the Midwest is very much on the table,
as evident in the low-to-moderate chances (20-50%) for snowfall
totals >6" over northern IA. Those in the Midwest should continue
to monitor the forecast closely as additional changes in the
placement and totals of the heaviest snowfall could still change
over the next 24 hours.

...Northeast...
Day 3...

There remains a good deal of uncertainty in the forecast
on Sunday with the GFS remaining aggressive in a more
amplified/phase solution compared to the ECMWF/CMC. The GFS is also
noticeably wetter than the GEFS over the Northeast. The ECMWF/CMC
camp shows a broader and less amplified 500mb trough over the Great
Lakes and southeast Canada, but enough 500mb PVA and lake-enhanced
snowfall bands are showing low chances (10-30%) for snowfall
totals >4" downwind of Lakes Erie and Ontario. Some minor impacts
to travel are possible as denoted by the WSSI-P showing low-to-
moderate chances (30-60%) for Minor Impacts on Sunday.

Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 052005
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
305 PM EST Fri Dec 5 2025

Valid 00Z Sat Dec 06 2025 - 00Z Tue Dec 09 2025


...Pacific Northwest, Northern & Central Rockies...
Days 1-3...

A highly active storm track with several significant atmospheric
rivers into the Northwest will usher in copious amounts of Pacific
moisture from the Pacific Northwest on east into the Northern and
Central Rockies the next few days. A steady barrage of >90th
climatological percentile PWATs will stream across the Pacific
Northwest into the Great Basin and Rockies through Saturday, with
another round of >90th percentile PWATs arriving in the Pacific
Northwest Sunday into Monday. Synoptic-scale forcing for ascent
will be aided by a persistent NW-SE oriented 250mb jet streak with
its diffluent left exit region overhead. Snow levels over the
Pacific Northwest will dip as low as 3,000ft while the Northern
Rockies generally hover around 4,000ft. As height falls occur over
the Northwest through Saturday, snow levels will drop to as low as
2,000ft. That being said, the heaviest snowfall will be confined to
elevations above 5,000ft in the Bitterroots, Lewis Range, and
Sawtooth, above 6,000ft in the Tetons, Absaroka, Big Horns, Bear
River, and Wasatch Ranges, and above 7,000ft in the central WY/CO
Rockies. Snow looks to taper off across the Central Rockies by
Saturday evening, but the next atmospheric river will deliver
another plume of Pacific moisture and another round of heavy
mountain snowfall across the Pacific Northwest and northern Rockies
Sunday into Monday.

WPC probabilities continue to be impressive on Day 1 across the
higher terrain from Glacier NP through Yellowstone NP including
portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of
NW WY, northern Utah, and into the Park Range of CO. Here, WPC
probabilities reach above 70% for 8+ inches, with locally higher
amounts of 1-2 feet generally above 6000 ft. Over the next few
days, WPC probabilities paint a wintry picture across many of the
Northern and Central Rockies, as well as the higher elevations of
the Cascades (above 5,000ft) with high chances (>70%) for
additional snowfall totals >18" in all of these listed ranges and
elevations through Sunday. In fact, the higher elevations of the
Lewis Range, Bitterroots, and Tetons have moderate-to-high chances
(50-80%) for snowfall totals >24". Moderate to heavy snow continues
later into Days 2 and 3 over the WA Cascades and northern Rockies,
though probabilities suggest less snowfall compared to the more
snowy stretches tonight into Saturday. The WSSI shows many areas of
Minor and Moderate Impacts across the Northern and Central
Rockies, including some locally Major Impacts. The Major Impact
potential areas (considerable disruptions; dangerous travel and
widespread closures) include areas along the Wasatch east of Salt
Lake City and the more remote areas of these Intermountain West
ranges. Residents in these mountain ranges should prepare for a
multi-day stretch of winter weather that results in difficult and
treacherous travel conditions.

...Northern Plains & Midwest...
Days 1-2...

A fast-moving clipper system, aided by a slug of Pacific moisture
combined with strengthening low-level frontogenesis and warm
advection, will support a swath of moderate to heavy snow from the
northern Plains into the Midwest the next couple of days. The band
of snow first starts to develop across the Dakotas late tonight
into Saturday morning, then heads for southern MN and
northern/central IA as it intensifies late Saturday afternoon and
evening. The band then begins to weaken by early Sunday morning as
the snow reaches the Lower Great Lakes and OH Valley.

The latest WPC probabilities have increased with this forecast,
now supporting probabilities of 50-90% for snowfall totals >4" for
locations that banding (mentioned above) is most likely across the
Midwest. However, given the favorable synoptic and mesoscale
processes at play, a swath of heavier and more impactful snow still
remains on the table, as evident in the low-to-moderate chances
(30-50%) for snowfall totals >6" over northern/central IA. By
Sunday, low probabilities (10-40%) of >4" of snow extend into
southern Wisconsin and northern Illinois as the quick-moving wave
weakens on its track into the Lower Great Lakes and OH Valley.
Those in the Midwest should continue to monitor the forecast
closely as additional changes in the placement and totals of the
heaviest snowfall could still change over the next 24 hours.

...Great Lakes & Northeast...
Days 1-3...

Periodic mid/upper level impulses rotating within a broad cyclonic
flow pattern will continue to support rounds of light-to-moderate
lake effect snowfall across the upper Great Lakes through Monday. A
cold frontal passage Saturday into early Sunday morning
revitalizes LES bands over the Michigan U.P. and downwind of Lake
Ontario over the Tug Hill. Then, the fast-moving clipper from the
Midwest races across the Great Lakes and Northeast later Sunday
into Monday, bringing more lake effect snow and likely a period of
steadier synoptic snow to interior portions of the Northeast and
northern New England. The latest 12Z guidance continues to suggest
a fairly flat mid/upper level shortwave as it passes over the
region, which would limit snowfall potential. That said, it would
not be surprising to see models trend a bit more amplified and more
snowy in future model cycles, so continue to monitor the forecast
in the coming days.

WPC probabilities show overall low chances (10-40%) of >4" of snow
across portions of northern Michigan downwind of Lake Superior and
Lake Michigan Saturday into Sunday. Low chances (10-30%) of >4" of
snow then extend downwind of Lake Erie and Lake Ontario and across
parts of northern New England Sunday into Monday.


Miller/Mullinax







$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 060746
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
246 AM EST Sat Dec 6 2025

Valid 12Z Sat Dec 06 2025 - 12Z Tue Dec 09 2025

...Central Rockies..
Day 1...

500mb height falls, the divergent left-exit region of a strong
250mb jet streak, and a plume of anomalous PWATs (above the 90th
climatological percentile per ECMWF) are all working together to
produce heavy mountain snow from the Wasatch, Uinta, and Wind River
ranges to the Rockies of southern WY and much of CO. Upslope
enhancement will be focused along the Wasatch and CO/WY Rockies
through this morning. As the core of the best moisture content
exits east this afternoon, snow will gradually taper off Saturday
night. WPC probabilities sport high chances (>70%) for additional
snowfall totals >12" in the Wasatch above 8,000ft and CO/WY
Rockies above 9,000ft. WPC's WSSI highlights Moderate Impacts at
these listed elevations with some localized Major Impacts in the
more remote peaks of the UT, WY, and CO Rockies.


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will continue to contend
with the lingering effects of the ongoing atmospheric river (AR)
through the remainder of the day Saturday. WPC probabilities show
high chances (>70%) for additional snowfall totals >8" in the more
remote reaches of the WA Cascades, the Bitterroots, Lewis Range,
and as far south as the peaks of the Absaroka and Tetons. A brief
ridge of high pressure builds in Saturday night before the round
of Pacific moisture arrives Sunday morning. Temperatures will be a
little milder this time around, confining most snowfall to the more
remote reaches of the Cascades. Pacific moisture will spill over
into the Northern Rockies Sunday night as the next atmospheric
river arrives on Monday. The Monday AR will be more intense with a
plume of >99th climatological PWATs engulfing much of the Pacific
Northwest by Monday afternoon. While the moisture influx is more
extensive, the strength of the WAA will keep snowfall to the more
remote reaches of the Cascades. However, moisture that spills over
into the Bitterroots and Lewis Range will have enough cold air to
support locally heavy snowfall. Over this weekend and through
Monday, WPC probabilities show moderate-to-high chances (50-80%)
for snowfall totals >12" in the WA Cascades above 5,000ft and along
the Lewis Range, which does include Glacier NP. Expect any
mountain passes that remain open to contend with potential closures
this weekend and into early next week.

...Northern Plains & Midwest...
Days 1-2...

Height falls ahead of an approaching 500mb vorticity maximum will
coincide with the divergent left-exit region of a 250mb jet streak
over the Northern Plains to support the development of low pressure
early this morning. A narrow band of 850mb WAA and FGEN over
eastern MT will pivot south and east towards southern ND and become
responsible for the initial band of snow this morning. As low
pressure deepens, a more organized 850mb low will form over
southern SD and central NE. A strengthening 850mb LLJ will direct a
surge of WAA in the 850-700mb layer ahead of the 850mb low.
Combined with a healthy 290K isentropic ascent amid SWrly flow, and
a moistening DGZ will ensue over southeast SD, northern IA, and
southern MN and periods of heavy snow will develop. WPC's Snowband
Probability Tracker depicts the potential for >1"/hr snowfall
rates over southeast SD beginning around midday and continuing over
northern IA through Saturday evening. After 00Z Sunday, the 850mb
low will weaken, taking on a positive tilt and becoming an open
wave. Light-to-moderate snow is expected through Saturday night
over northern IL and southern WI (including the Milwaukee and
Chicago metro areas), with light snow possible across the Great
Lakes on Sunday.

WPC probabilities show northern IA as having the best odds of
seeing the heaviest snowfall of the event with moderate chances
(40-60%) for snowfall totals >6". Probabilities suggest I-35
located north of Des Moines and south of I-90 have low chances
(10-20%) for localized amounts over 8". Elsewhere, the area
spanning Sioux Falls on south and east through southern MN and
eastern ND all sport >50% chances for >4" of snowfall. The WSSI
shows Minor Impacts from the Sioux Falls area of southeast SD to as
far east as the Milwaukee/Chicago metro areas due to the snowfall
Saturday night into Sunday morning. Across eastern MT and southwest
ND, WPC probabilities show low- to- moderate chances (30-50%) for
snowfall >2", but probabilities for >4" are generally <10%,
implying that most totals are likely to range between 1-4" through
Saturday afternoon.

It is worth noting bitterly cold temperatures will follow in wake
of this system Saturday night and through Sunday. By Sunday
morning, temperatures will be in the single digits across much of
the Midwest and lows below zero Sunday night. Any snow that falls
will likely stick around for a couple days, resulting in daily
recurrences of icy roads and the potential for black ice.

...Great Lakes & Northeast...
Days 1-3...

A series of upper level disturbances tracking across the Great
Lakes and into the Northeast will cause both LES bands and some synoptically-focred snow across these regions this weekend and into
early next week. Some LES streamers off Lakes Superior, Erie, and
Ontario will keep accumulating snow in the forecast in the usual
snow belts of Michigan's U.P., the "Tip of the Mitt" in Michigan,
and across western NY. By Sunday morning the upper trough
responsible for the Midwest storm on Saturday will make its way
through these regions with light-to-moderate snowfall across
Michigan and much of the Northeast (minus the I-95 corridor
megalopolis). Most snowfall totals will range between 1-4",
although some of the LES belts may manage to see some snowfall
totals eclipse 4" on Sunday. It is possible an inverted trough axis
over the Gulf of Maine could produce locally heavy snow along the
coast of ME, but the trough is a progressive one and should limit
totals from being overly heavy (1-4" most likely). Lastly, while
high pressure builds in over the Northeast on Monday, an Alberta
Clipper makes its way toward the Upper great Lakes by Monday
evening with more light-to-moderate snow expected.

WPC probabilities over the next three days (Sat-Sun-Mon) show
moderate-to-high chances (50-80%) for snowfall totals >4" in the
typical LES belts of Michigan's U.P., northern Michigan, and
downwind of Lakes Erie and Ontario. When it comes to >8" of
snowfall, it is the eastern Michigan U.P. and northwest Michigan
where low-to-moderate chances (30-50%) are present. The WSSI shows
Minor Impact potential downwind of Lakes Erie and Ontario, which
does include the Buffalo metro area.

...Southern Appalachians...
Days 2-3...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. WPC probabilities show low-to-moderate
chances (30-50%) for snowfall totals >2" in portions of the VA/NC
Blue Ridge and Potomac Highlands of WV. Some localized totals could
top 4" in the VA/NC Blue Ridge.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 061854
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
154 PM EST Sat Dec 6 2025

Valid 00Z Sun Dec 07 2025 - 00Z Wed Dec 10 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will continue to contend
with the lingering snow during the D1 period as a shortwave tracks
across the region over a broad western U.S. ridge ahead of a strong
atmospheric river (AR) set to surge into WA/OR on D2, with lowering
snow levels across the Cascades on D3. Snow levels largely start
out low around 3,000-4,000 ft, but rapidly rise across the Pacific
Northwest on Sunday above 5,000 ft and as the strong AR approaches
on Monday these values increase to above 6,000 ft in the northern
WA Cascades and above 7,000 ft from Mt. Rainer southward.
Meanwhile, snow levels also rise across the northern Rockies to
above 5,000-6,000 ft as well before dropping on D3 as the AR ends
and the associated shortwave ejects into the northern Plains. For
the 72-hr period ending 00z 12/10, WPC probabilities for more than
12 inches are high (70-90%) across the WA Cascades above 6,000 ft,
as well as parts of the northern Rockies in ID, northwest MT, and
northwest WY above 6,000-7,000 ft.


...Midwest/Great Lakes/Northeast...
Days 1-3...

Fast-moving clipper system currently impacting parts of the
northern Plains and Midwest with heavy snow this afternoon will
swing across IA/northern IL/southern WI tonight into early Sunday
and produce a storm total swath of up to 4-8 inches of fresh
snowfall. Height falls ahead of an approaching 500mb vorticity
maximum will coincide with the divergent left-exit region of a
250mb jet streak to support the developing low pressure system. A
strengthening 850mb LLJ will direct a surge of WAA in the 850-700mb
layer ahead of the 850mb low. Combined with a healthy 290K
isentropic ascent amid SWrly flow, and a moistening DGZ will ensue
over northern IA this evening and periods of heavy snow will
develop. Snowfall rates may briefly exceed 1"/hr within this east-
west corridor just north of the 850mb FGEN extending from northern
IA into southern WI/northern IL. However, the 850mb low will begin
to quickly weaken tonight, taking on a positive tilt and becoming
an open wave. Light- to- moderate snow is expected through Sunday
morning into northern IN and the southern L.P. of MI.

WPC probabilities beginning at 00z Sunday show eastern IA to
northern IL (including the Chicago metro) as having the highest
chances (40-80%) for snowfall totals more than 4 inches. It is
worth noting bitterly cold temperatures will follow in wake of this
system Saturday night and through Sunday. By Sunday morning,
temperatures will be in the single digits across much of the
Midwest and lows below zero Sunday night. Any snow that falls will
likely stick around for a couple days, resulting in daily
recurrences of icy roads and the potential for black ice.

This system along with another upper level disturbance by D3 tracking
across the Great Lakes and into the Northeast will cause both LES
bands and some synoptically- forced snow across these regions
Sunday and into early next week. Some LES streamers off Lakes
Superior, Erie, and Ontario will keep accumulating snow in the
forecast in the usual snow belts of Michigan's U.P., the "Tip of
the Mitt" in Michigan, and across western NY. By Sunday morning the
upper trough responsible for the Midwest storm on Saturday will
make its way through these regions with light-to- moderate snowfall
across Michigan and much of the Northeast (minus the I-95 corridor megalopolis). Most snowfall totals will range between 1-4",
although some of the LES belts may manage to see some snowfall
totals eclipse 4" on Sunday. Lastly, while high pressure builds in
over the Northeast on Monday, an Alberta Clipper makes its way
toward the Upper Great Lakes by Monday evening with more light-to-
moderate snow expected. Strong southerly flow ahead of this system
may actually produce a band of heavy lake effect snow oriented from
Lake Michigan aimed northward into the eastern U.P.

WPC probabilities over through Tuesday show moderate-to-high
chances (50-80%) for snowfall totals >4" in the typical LES belts
of Michigan's U.P., northern Michigan, and downwind of Lakes Erie
and Ontario. When it comes to >8" of snowfall, it is the eastern
Michigan U.P. where moderate chances (50-70%) are present.


...Southern Appalachians & Mid-Atlantic...
Day 2...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. As the upper trough sharpens on Monday over
the Mid-Atlantic and low pressure deepens over the Gulf Stream off
the Southeast coastline, some snow may also extend eastward into
southern VA and far northern NC. QPF and therefore snow amounts
have trended up with the latest guidance and should be monitored
over the next day or so for potentially impactful accumulating
snowfall. WPC probabilities currently show low- to- moderate
chances (30-50%) for snowfall totals >2" in portions of the VA/NC
Blue Ridge and Potomac Highlands of WV. Some localized totals could
top 4" in the VA/NC Blue Ridge.


...Northern Plains & Upper Midwest...
Day 3...

By the second half of D3 (12z 12/9-00z 12/10) a potent shortwave
within the divergent left-exit region of a strong upper jet
extending as far westward as the central Pacific Ocean will enter
the northern Plains and likely produce a narrow stripe of heavy
snowfall. Snow will be associated with WAA on the front-end and a
trailing inverted trough. The thermal gradient will be tight and
support intense snowfall rates at times just north of the warm
front, but with uncertainty remaining as guidance maintains some
latitudinal spread and timing differences in the low track. Strong
winds are also likely on the backside of the system as models
deepen this low into the 980s, so blowing snow could be a concern
should these winds overlap with a snowpack. Current WPC
probabilities for more than 4 inches of snow through 00z Wednesday
are moderate (40-70%) across north-central ND through central MN.
However, additional snow is likely after 00z Wednesday and
continuing further east into WI and the Great Lakes region.


Mullinax/Snell





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 070816
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Sun Dec 7 2025

Valid 12Z Sun Dec 07 2025 - 12Z Wed Dec 10 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Today, PWATs start out around
the 90th climatological percentile throughout the Northwest, before
a more impressive plume of PWATs above the 99th climatological
percentile stream in on Monday. Even on Tuesday, as the subtropical
ridge expands a little farther north, a fire-hose of Pacific
moisture will continue into the Pacific Northwest that spills into
the Northern Rockies as well. Add in steady synoptically-forced
ascent aloft from a strong 250mb jet stream and persistent upslope
flow into many of these mountains ranges, and the recipe is for
heavy snowfall from the Olympics and Cascades to the western WY
Rockies.

Today, snow levels largely look to start out around 3,000-4,000
ft, but rapidly rise across the Pacific Northwest above 5,000ft.
As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,000 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on D3 as the AR
orients itself farther south as a shortwave trough ejects into the
northern Plains. Starting this morning and lasting through early
Wednesday morning, 72-hr WPC probabilities for more than 12 inches
are high (70-90%) across the WA Cascades above 5,000 ft, as well
as parts of the northern Rockies in ID, western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas
of low-to-moderate chances (20-50%) for localized snowfall totals

30" in the more remote reaches of these regions through Tuesday

night.


...Great Lakes & Northeast...
Days 1-3...

This morning, the upper trough responsible for the Midwest storm
on Saturday will generate light-to-moderate snowfall across
Michigan and much of the Northeast (minus the I-95 corridor
megalopolis). Most snowfall totals will range between 1-4",
although some areas within the Tug Hill and Adirondacks may manage
to see localized snowfall totals eclipse 4" on Sunday. The upper-
level disturbance may produce a small area of low pressure off the
Maine coast that produces a fast moving band of snow over Downeast
Maine Sunday night. WPC probabilities do depict low chances
(10-30%) for snowfall totals >4" Monday night.

By Monday night, as high pressure builds in over the Northeast, an
Alberta Clipper makes its way toward the Upper Great Lakes Monday
evening with more light-to-moderate snow expected. Guidance is
coming into better agreement that strong SWrly flow ahead of the
Clipper will produce a band of heavy lake effect snow oriented from
Lake Michigan and far northwest Michigan aimed northward into the
eastern U.P.. WPC probabilities through Tuesday show moderate-to-high
chances (50-80%) for snowfall totals >4" in over the eastern
Michigan U.P. and northwest Michigan. The eastern Michigan U.P.
sports the highest chances for >8" of snowfall (30-50%). As the
Clipper's warm front moves east, sufficient 290K isentropic ascent
and 850-700mb WAA will give rise to snow over the eastern Great
Lakes and northern New England by Tuesday afternoon. Immediately
downwind of Lakes Erie and Ontario, snowfall totals will generally
range between 1-4". However, the Tug Hill has moderate chances
(40-60%) for snowfall totals >4" through early Wednesday morning.


...Southern Appalachians & Mid-Atlantic...
Days 1-2...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest Monday morning but taper
off by Monday evening. This storm could have a surprise or two up
its sleeve as the 500mb vorticity maximum reaches NC Monday
afternoon, with some guidance showing some 850mb low development
off the coast of NC's Outer Banks. Should easterly low-level winds
increase, sufficient low-level WAA and moisture advection could
create a band of snow that results in a quick hitting 1-3" snow
event from as far north as the Richmond metro area on south along
I-95 and I-85 towards the Raleigh/Durham area. WPC probabilities
currently show low chances (10-30%) for snowfall totals >4" in
portions of the VA/NC Blue Ridge and Potomac Highlands of WV, but
it is possible those chances increase should the influences of the
500mb trough prove more substantial. This has the potential to
cause slick travel conditions for the Monday evening commute in
southern VA and northern NC.


...Northern Plains & Upper Midwest...
Day 3...

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be sub-990mb, which ranks below the 1st
climatological percentile for this time of year. As the storm works
its way across the Dakotas Tuesday morning, impressive 290K
isentropic lift and corresponding 850-700mb FGEN will not only
help to sustain this potent clipper, but foster a potent band of
snow northeast of the 850mb low track. There is the potential for
an icy wintry mix just along and north of the surface warm front as
a protruding >0C warm nose forces snow to melt into the form of
sleet or freezing rain. But the storm's fast motion should limit
the impacts to around minor impacts (ice accretions less than a
tenth of an inch most likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. WPC probabilities show a swath of
moderate chance probabilities (40-60%) for snowfall totals >4" from
northeast ND on south and east through the Upper Midwest and the
northern half of Michigan's Mitten. Note there are also low-to-
moderate chance probabilities (20-50%) for totals >6", which does
show up on several deterministic guidance members.

While the storm's speedy forward motion should help to reduce the
chances for more prolific snowfall totals, hourly snowfall rates of

1"/hr combined with gusty winds will allow for Minor Impacts at

the very least. This is supported by the WSSI-P which depicts
moderate-to-high chances (50-70%) for Minor Impacts on Tuesday from
northern ND all the way to northern MI. Residents in the Upper
Midwest and Great Lakes should continue to monitor this storm
closely, as should residents in the Northeast as probabilistic
guidance shows measurable snowfall from this system is possible on
Wednesday.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 072021
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Sun Dec 7 2025

Valid 00Z Mon Dec 08 2025 - 00Z Thu Dec 11 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Tonight, PWATs start out
around the 90th climatological percentile throughout the Northwest,
before a more impressive plume of PWATs above the 99th
climatological percentile stream in on Monday. Even on Tuesday and
Wednesday, as the subtropical ridge expands a little farther
north, a fire- hose of Pacific moisture will continue into the
Pacific Northwest that spills into the Northern Rockies as well.
Add in steady synoptically-forced ascent aloft from a strong 250mb
jet stream and persistent upslope flow into many of these mountains
ranges, and the recipe is for heavy snowfall from the Olympics and
Cascades to the western WY Rockies above the wavering high snow
levels.

Tonight, snow levels largely look to start out around 5,000ft. As
the strong AR and its associated WAA aloft approaches on Monday,
these values increase to above 6,500 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on Tuesday as
the AR orients itself farther south as a shortwave trough ejects
into the northern Plains. Then, snow levels once again rise on
Wednesday as levels increase above 6,000 ft from southern
Washington to west-central MT. Starting this evening and lasting
through early Wednesday evening, 72-hr WPC probabilities for more
than 12 inches are high (70-90%) across the WA Cascades above 5,000
ft, as well as parts of the northern Rockies in ID, western MT,
and western WY above 6,000-7,000 ft. WPC probabilities even show
speckled areas of low- to-moderate chances (20-50%) for localized
snowfall totals >30" in the more remote reaches of these regions
through Wednesday.


...Southern Appalachians & Mid-Atlantic...
Days 1...

A quick moving 500mb trough will track from the TN Valley Sunday
night to the Southeast Coast by Monday afternoon. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest during the day on Monday
but taper off by Monday evening. As the 500mb vorticity maximum
reaches NC Monday afternoon, a weak 850mb low development off the
coast of NC's Outer Banks will allow for easterly low- level winds
to increase. This combined with sufficient low-level WAA and
moisture advection may create a band of snow that results in a
quick hitting 1-3" snow event in southern VA and northern NC as
far north as the Richmond metro area and south along I-95 and I-85
towards the Raleigh/Durham area. WPC probabilities currently show
low chances (20-40%) for snowfall totals >4" in portions of the
VA/NC Blue Ridge and Potomac Highlands of WV. Probabilities for

2" are 40-60% east of the Blue Ridge across southern VA and could

lead to slippery road conditions to start the workweek.


...Northern Plains/Upper Midwest/Great Lakes...
Days 2-3...

By Monday night, as high pressure builds in over the Northeast, the
first in a parade of "clipper" systems makes its way toward the
Upper Great Lakes with more light-to-moderate snow expected.
Guidance continues to highlight that strong SWrly flow ahead of
the Clipper will produce a band of heavy lake effect snow oriented
from Lake Michigan and far northwest Michigan aimed northward into
the eastern U.P.. WPC probabilities through Tuesday show moderate-
to- high chances (50-80%) for snowfall totals >6" in over the
eastern Michigan U.P. The eastern Michigan U.P. As the clipper's
warm front moves east, sufficient 290K isentropic ascent and
850-700mb WAA will give rise to snow over the eastern Great Lakes
and northern New England by Tuesday afternoon. Immediately
downwind of Lakes Erie and Ontario, snowfall totals will generally
range between 1-4". However, the Tug Hill has moderate chances
(40-60%) for snowfall totals >4" through early Wednesday morning.

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be sub-990mb, which ranks below the 1st
climatological percentile for this time of year. As the storm works
its way across the Dakotas Tuesday morning, impressive 290K
isentropic lift and corresponding 850-700mb FGEN will not only help
to sustain this potent clipper, but foster a potent band of snow
northeast of the 850mb low track. There is the potential for an icy
wintry mix just along and north of the surface warm front as a
protruding >0C warm nose forces snow to melt into the form of sleet
or freezing rain. But the storm's fast motion should limit the
impacts from freezing rain to around minor impacts (ice accretions
less than a tenth of an inch most likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. WPC probabilities show a swath of
moderate chance probabilities (40-70%) for snowfall totals >4"
from northeast ND on south and east through the Upper Midwest and
the northern half of Michigan's Mitten. Note there are also low-to-
moderate chance probabilities (20-40%) for totals >6", which does
show up on several deterministic guidance members. There has
continued to be some latitudinal spread in guidance with AIFS and
AIGFS guidance along with the operational GFS leaning towards a
more southern track that gets central MN and southern WI into
chances for heavy snow.

While the storm's speedy forward motion should help to reduce the
chances for more prolific snowfall totals, hourly snowfall rates of

1"/hr combined with gusty winds will allow for minor to moderate

impacts at the very least. This is supported by the WSSI-P which
depicts high chances (60-90%) for Minor Impacts on Tuesday from
northern ND all the way to northern MI. Residents in the Upper
Midwest and Great Lakes should continue to monitor this storm
closely, as should residents in the Northeast as probabilistic
guidance shows measurable snowfall from this system is possible on
Wednesday.


Mullinax/Snell




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 080843
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
343 AM EST Mon Dec 8 2025

Valid 12Z Mon Dec 08 2025 - 12Z Thu Dec 11 2025


...Pacific Northwest & Northern Rockies...
Days 1-3...

The Pacific Northwest and Northern Rockies will face a steady
barrage of Pacific moisture over the next few days thanks to a
multi-day strong atmospheric river that is pinned between a strong
subtropical ridge off the coast of CA and a stalled, positively-
tilted upper low in the Gulf of AK. Today, PWATs above the 99th
climatological percentile will engulf much of the Northwest. Even
on Tuesday and into Wednesday, as the subtropical ridge expands a
little farther north, a fire-hose of Pacific moisture will continue
into the Pacific Northwest that spills into the Northern Rockies
as well. Add in steady synoptically-forced ascent aloft from a
strong 250mb jet stream and persistent upslope flow into many of
these mountains ranges, and the recipe is for heavy snowfall from
the Olympics and Cascades to the western WY Rockies above the
wavering high snow levels.

As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,500 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on Tuesday as
the AR orients itself farther south as a shortwave trough ejects
into the northern Plains. Then, snow levels once again rise on
Wednesday as levels increase above 6,000 ft from southern
Washington to west-central MT. Through Wednesday night, 72-hr WPC
probabilities for >18" are high (>70%) across the WA Cascades
above 5,000 ft, as well as parts of western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas of low-to-moderate chances (20-50%) for localized snowfall totals

30" in the more remote reaches of these regions through Wednesday.

...Southern Appalachians & Mid-Atlantic...
Days 1...

A 500mb trough tracking over the TN Valley this morning will race
east and off the Southeast Coast by this evening. 500mb PVA ahead
of the upper trough will be paired with easterly low-level flow
that allows for some upslope enhancement along the southern
Appalachians. Snow will be at its heaviest during the day on Monday
as Atlantic moisture is directed west to the north of a weak 850mb
low tracking across northern NC. This combined with sufficient
low-level WAA will generate a band of snow that results in a quick
hitting 1-4" snow event in southern VA and northern NC, to as far
north as the Richmond metro area and south along I-95 and I-85
towards the Raleigh/Durham area. WPC probabilities currently show
low chances (20-40%) for snowfall totals >4" in portions of the
VA/NC Blue Ridge, the Potomac Highlands of WV, and southern VA
south of the Richmond metro area. Localized snowfall totals of 5-6"
are quite possible, especially in the VA Blue Ridge. Probabilities
for >2" are 40-60% east of the Blue Ridge across southern VA and
is likely lead to slippery road conditions to start the workweek.
Latest WSSI does suggest Minor Impacts for most affected locations,
with a narrow Moderate Impacts (hazardous driving conditions) area
stretching from Roanoke, VA to the Richmond/Petersburg metro area
and as far east as Williamsburg, VA.


...Great Lakes & Northeast...
Days 1-2...

Tonight, as high pressure builds in over the Northeast, the first
in a parade of "clipper" systems tracks over the Upper Great Lakes
with more light-to-moderate snow expected. Guidance continues to
highlight that strong SWrly flow ahead of the clipper will produce
a band of heavy lake effect snow oriented from Lake Michigan and
far northwest Michigan aimed northward into the eastern U.P.. WPC
probabilities through Tuesday show moderate-to- high chances
(50-80%) for snowfall totals >6" over the eastern Michigan U.P.. As
the clipper's warm front moves east, sufficient 290K isentropic
ascent and 850-700mb WAA will give rise to snow over the eastern
Great Lakes and northern New England by Tuesday afternoon.
Immediately downwind of Lakes Erie and Ontario, snowfall totals
will generally range between 1-4".


...Northern Plains, Midwest, Great Lakes, & Northeast...
Days 2-3...

By Tuesday morning, a vigorous 500mb shortwave trough with origins
from the large Gulf of AK longwave trough will race towards the
Northern Plains. Given its origins, this "Alberta Clipper" will be
more intense than most clippers. This is because it will have
exceptional synoptic-scale forcing aloft in the form of a roaring
150kt 250mb jet streak, plus anomalous moisture associated with the
strong AR over the Pacific Northwest. By 18Z Tuesday, the
clipper's MSLP looks to be in the mid-upper 980mb range, which
ranks below the 1st climatological percentile for this time of
year. As the storm works its way across the Dakotas Tuesday
morning, impressive 290K isentropic lift and corresponding
850-700mb FGEN will not only help to sustain this potent clipper,
but foster a potent band of snow northeast of the 850mb low track.
There is the potential for an icy wintry mix just along and north
of the surface warm front as a protruding >0C warm nose forces snow
to melt into the form of sleet or freezing rain. But the storm's
fast motion should limit the impacts from freezing rain to around
minor impacts (ice accretions less than a tenth of an inch most
likely).

By Tuesday night, the storm will remain in the mid-980s for
pressure as it races through WI and into MI by Wednesday morning.
WAA out ahead of the storm is likely to cause periods of snow to
envelope the eastern Great Lakes that include areas such as
northwest PA and western NY. From the Northern Plains the the Great
Lakes, not only will snow be problematic for traveling, but gusty
winds are likely to cause blowing and drifting across roads and
cause reduced visibilities. Recent 00Z guidance suite has given
some credence to the EC-AIFS and GFSAI being more on the southern
track of guidance, but there are still a few members that remain a
little farther north. WPC probabilities show a swath of high-chance probabilities (>70%) for snowfall totals >4" from northeast ND on
south and east through the Upper Midwest and the northern half of
Michigan's Mitten. Note that probabilities have increased to
moderate-chance level (40-60%) for totals >6", which is increasing
confidence in a travel-disrupting winter storm on Tuesday.

While the storm's speedy forward motion should help to cap the
chances for more substantial snowfall totals, hourly snowfall rates
of >1"/hr combined with gusty winds will allow for minor to
moderate impacts, some of which will occur during the Monday
evening commute. This is supported by the WSSI-P which depicts high
chances (>70%) for Minor Impacts on Tuesday from northern ND all
the way to northern MI. Residents in the Upper Midwest and Great
Lakes should continue to monitor this storm closely, as should
residents in the Northeast as probabilistic guidance shows
measurable snowfall from this system is possible on Wednesday.

By Wednesday morning, the storm will race into Ontario with strong
850-700mb WAA overrunning a very cold air-mass in the Northeast.
Look for periods of snow to occur from the Central Appalachians on
north through the northern Appalachians. WPC probabilities show moderate-to-high chances (50-70%) for >6" in the Adirondacks, Tug
Hill, the Green and White Mountains. Some valleys in northern New
England have moderate chances (40-60%) for >2" of snowfall before
any issues with mixing or changing to rain occur. As the storm
tracks through the St. Lawrence River Valley, cyclonic flow of the
Great Lakes will spark additional LES bands over the typical snow
belts, including some upslope ascent into the central Appalachians
through early Wednesday morning.


Mullinax/Snell




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 081948
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Mon Dec 8 2025

Valid 00Z Tue Dec 09 2025 - 00Z Fri Dec 12 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

Prolonged moisture spilling east from a strong atmospheric river
(AR) with multiple embedded waves will spread heavy snow into the
Intermountain West through late-week.

The strong AR will surge onshore the Pacific Northwest this
evening as a shortwave lifts into British Columbia with
impressively confluent and zonal flow pushing into WA/OR. IVT
probabilities for 750 kg/m/s exceed 90% during this time near the
WA/OR border, aided by a powerful Pacific jet streak of over 150
kts moving into British Columbia. This will be the beginning of a
long duration and impressive plume of IVT surging from the Pacific
Northwest and then spilling across the terrain and diving into the
High Plains through late week. While there will be multiple surges
of elevated IVT (and so not a continuous period of heavy
precipitation), in general the entire forecast period will be
unsettled, and IVT exceeding the CFSR climatology is progged via
NAEFS for multiple periods Wednesday and Thursday - indicating the
impressive available moisture associated with this system.

As with most ARs, the forcing and moisture will be attributed to
potent WAA, and this will drive snow levels to well above normal
levels for early December, likely reaching 8000-9000 ft in many
areas west of the Continental Divide and south of a wavering
stationary front/baroclinic boundary that will not only be a
demarcation for colder temperatures, but also provide a surface for
a subtle increase in isentropic ascent and fgen across the region.
Since snow levels south of this front will be so high, any heavy
snow should be confined to only the higher peaks of the northern WA
Cascades, far Northern Rockies, and into NW WY D1-D2 where WPC
probabilities are continuously high (above 70%) for 6+ inches both
days, especially in the northern WA Cascades and higher elevations
surrounding Yellowstone NP.

Then during D3, more significant snowfall becomes probable east of
the Northern Rockies in response to Arctic high pressure sinking
south out of Saskatchewan, driving a cold front to bank into the
terrain from the NE. This will sharpen the baroclinic gradient,
intensifying the resultant fgen, and increase isentropic ascent as
IVT continues to surge eastward beneath the potent Pacific jet
streak arcing to the southeast from British Columbia. While there
is considerable spread still in the placement and coverage of
precipitation D3, confidence is increasing in an axis of heavy snow
spread NW to SE beneath this jet streak and just north of the
front across MT and into the Dakotas. Current WPC probabilities for
more than 6 inches of snow are as high as 70% in the Northern
Rockies near Glacier NP above 7000 ft, with more expansive, but
low-end probabilities (10-30%) for 6+ inches extending well into
the High Plains of MT.


...Northern Plains through the Great Lakes and Northeast...
Days 1-3...

Two distinct fast-moving shortwaves will race across the region
through late-week bringing several rounds of wintry precipitation.

The first of these will stem from a potent vorticity maxima and
associated shortwave trough which will dig out of Manitoba this
evening, reaching Michigan by Tuesday morning, and then crossing
New England to exit into Canada by Wednesday morning. This feature
will remain of modest amplitude and the corresponding downstream
jet streak does not appear well positioned for any enhanced deep
layer ascent to cause cyclogenesis. Despite this, some increased
isentropic ascent from 280K-290K will cause a swath of moderate to
heavy snowfall tonight through Tuesday, with the speed of the
system the primary limiting factor to snowfall. Favorable ascent
into the DGZ will likely yield briefly heavy snow rates,
especially in MN/WI/MI before weakening into New England, with
moderate snow accumulations expected. WPC probabilities for even 2"
of snow are quite limited for this event, but periods of moderate
to briefly heavy snow could create hazardous travel for the monday
commutes for parts of WI, MI, and into Upstate NY.

Immediately in the wake of this first system a second, and likely
more amplified, shortwave and accompanying vorticity lobe, will
swing southeast out of Alberta/Saskatchewan and dive into the
Northern Plains by Tuesday afternoon. This shortwave is progged to
deepen during its progression, and while it should maintain a
positive tilt through its lifetime, it will gain amplitude and dive
farther south than the initial impulse. The resulting impressive
height falls will overlap efficiently with the LFQ of an
impressive Pacific jet streak following in its wake, producing
intense deep layer lift which will help deepen a surface low
/Alberta Clipper/. There is continued spread among the various
deterministic models (generally a global vs. high-res dichotomy) and
their accompanying ensemble spreads, but in general the
differences are small leading to high confidence in a track from
ND Tuesday aftn to lower Michigan Wednesday morning to northern
Maine/Quebec Thursday morning.

In addition to the robust synoptic lift, ascent will become
enhanced through a progressive overlap of 285K-295K moist
isentropic ascent (mixing ratios as high as 4g/kg) with 850-600mb
fgen. This will be well aligned to the most impressive left-exit
diffluence, and directed into the primary snow growth region /DGZ/,
suggesting some banded snow with heavier snow rates occurring N/E
of the low- level circulation. This is reflected by the WPC
prototype snowband tool suggesting at least 1"/hr snowfall rates
diving across the region. While the temporal duration of these snow
rates,owing to the speed of the system, should cap the snowfall
amounts, some secondary banding is possible on the NW side of the
low in response to intensifying deformation, especially Tuesday
night into Wednesday. This may lead to some locally higher snowfall
totals, but at this time, WPC probabilities D1 for 4+ inches of
snowfall reach 50-70% from far eastern ND through much of northern
MN (south of the Arrowhead, however), with a more pronounced stripe
of 50+% probabilities for more than 4 inches on D2 across this same
area and extending into WI and lower MI. The transient nature of
the system will limit the high-end snowfall, but some areas may
receive as much as 8 inches of snowfall.

Additionally, south of this axis of heaviest snow, a transition
zone of mixed precipitation, including freezing rain is expected,
leading to at least modest ice accretion. While light freezing rain
is expected from far eastern MT through lower MI, the greatest
chance (10-30%) for more than 0.1" of icing exists across ND.

As this storm exits the Great Lakes and moves into Ontario D3, the
downstream strong WAA will overrun a very cold antecedent airmass.
This will create a broadening plume of wintry precipitation,
falling primarily as snow from Upstate NY through northern New
England, with some mixing, including periods of freezing rain,
expected farther south into the northern Mid-Atlantic and southern
New England. Total accumulations of wintry precipitation should be
less than areas upstream, but WPC probabilities late D2 into D3 for
4+ inches of snow reach 50-90% for portions of western PA and
across the southern Adirondacks, Greens, Whites, and terrain of
northern ME.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes and into the Central Appalachians. While some
of this snow will fall on top of the synoptic snow noted above
(and is included in the snowfall probabilities), and additional 4+
inches of snow has a moderate risk of occurring across the Tug Hill
Plateau and Chautauqua Ridge D3. Similar probabilities for 4+
inches of snow exist in the higher terrain of WV as well where
upslope flow and gusty winds could create hazardous impacts.



Weiss


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 090828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Tue Dec 9 2025

Valid 12Z Tue Dec 09 2025 - 12Z Fri Dec 12 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

Prolonged moisture spilling east from a strong atmospheric river
(AR) with multiple embedded waves will spread heavy snow into the
Intermountain West through late-week.

The strong AR will surge onshore the Pacific Northwest this
evening as a shortwave lifts into British Columbia with
impressively confluent and zonal flow pushing into WA/OR. IVT
probabilities for 750 kg/m/s exceed 90% during this time near the
WA/OR border, aided by a powerful Pacific jet streak of over 150
kts moving into British Columbia. This will be the beginning of a
long duration and impressive plume of IVT surging from the Pacific
Northwest and then spilling across the terrain and diving into the
High Plains through late week. While there will be multiple surges
of elevated IVT (and so not a continuous period of heavy
precipitation), in general the entire forecast period will be
unsettled, and IVT exceeding the CFSR climatology is progged via
NAEFS for multiple periods Wednesday and Thursday - indicating the
impressive available moisture associated with this system.

As with most ARs, the forcing and moisture will be attributed to
potent WAA, and this will drive snow levels to well above normal
levels for early December, likely reaching 8000-9000 ft in many
areas west of the Continental Divide and south of a wavering
stationary front/baroclinic boundary that will not only be a
demarcation for colder temperatures, but also provide a surface for
a subtle increase in isentropic ascent and fgen across the region.
Since snow levels south of this front will be so high, any heavy
snow should be confined to only the higher peaks of the northern WA
Cascades, far Northern Rockies, and into NW WY D1-D2 where WPC
probabilities are continuously high (above 70%) for 6+ inches both
days, especially in the northern WA Cascades and higher elevations
surrounding Yellowstone NP.

Then during D3, more significant snowfall becomes probable east of
the Northern Rockies in response to Arctic high pressure sinking
south out of Saskatchewan, driving a cold front to bank into the
terrain from the NE. This will sharpen the baroclinic gradient,
intensifying the resultant fgen, and increase isentropic ascent as
IVT continues to surge eastward beneath the potent Pacific jet
streak arcing to the southeast from British Columbia. With latest
WSO and WSSI-P guidance now showing >50% probabilities for snowfall
totals surpassing warning criteria and Moderate Impacts, confidence
is increasing in an axis of heavy snow spread NW to SE beneath
this jet streak and just north of the front across MT through D3, and
into the western Dakotas by D4. Current WPC probabilities for more
than 8 inches of snow are as high as 70% in the Northern Rockies
near Glacier NP above 7000 ft, with a larger footprint of
moderate-to-high chances (50-80%) across the heart of Big Sky
Country that includes mountain ranges such as the Little Belt, Big
Snowy, and Absaroka.


...Northern Plains through the Great Lakes and Northeast...
Days 1-3...

Two distinct fast-moving shortwaves will race across the region
through late-week bringing several rounds of wintry precipitation.

The first of these will stem from a potent vorticity maxima and
associated shortwave trough which will dig out of Manitoba this
evening, reaching Michigan this morning, and then crossing New
England to exit into Canada by Wednesday morning. This feature will
remain of modest amplitude and the corresponding downstream jet
streak does not appear well positioned for any enhanced deep layer
ascent to cause cyclogenesis. Despite this, some increased
isentropic ascent from 280K-290K will cause a swath of moderate to
heavy snowfall tonight through Tuesday, with the speed of the
system the primary limiting factor to snowfall. Favorable ascent
into the DGZ will likely yield briefly heavy snow rates, especially
in MN/WI/MI before weakening into New England, with moderate snow
accumulations expected. WPC probabilities for even 2" of snow are
quite limited for this event, but periods of moderate to briefly
heavy snow could create hazardous travel for the monday commutes
for parts of WI, MI, and into Upstate NY.

Immediately in the wake of this first system a second, and likely
more amplified, shortwave and accompanying vorticity lobe, will
swing southeast out of Alberta/Saskatchewan and dive into the
Northern Plains by this afternoon. This shortwave is progged to
deepen during its progression, and while it should maintain a
positive tilt through its lifetime, it will gain amplitude and dive
farther south than the initial impulse. The resulting impressive
height falls will overlap efficiently with the LFQ of an impressive
Pacific jet streak following in its wake, producing intense deep
layer lift which will help deepen a surface low /Alberta Clipper/.
There is continued spread among the various deterministic models
(generally a global vs. high-res dichotomy) and their accompanying
ensemble spreads, but in general the differences are small leading
to high confidence in a track from ND Tuesday aftn to lower
Michigan Wednesday morning to northern Maine/Quebec Thursday
morning.

In addition to the robust synoptic lift, ascent will become
enhanced through a progressive overlap of 285K-295K moist
isentropic ascent (mixing ratios as high as 4g/kg) with 850-600mb
fgen. This will be well aligned to the most impressive left-exit
diffluence, and directed into the primary snow growth region /DGZ/,
suggesting some banded snow with heavier snow rates occurring N/E
of the low- level circulation. This is reflected by the WPC
prototype snowband tool suggesting at least 1"/hr snowfall rates
diving across the region. While the temporal duration of these snow
rates, owing to the speed of the system, should cap the snowfall
amounts, some secondary banding is possible on the NW side of the
low in response to intensifying deformation, especially Tuesday
night into Wednesday. This may lead to some locally higher snowfall
totals, but at this time, WPC probabilities D1 for 4+ inches of
snowfall reach 50-70% from far eastern ND through much of northern
MN (south of the Arrowhead, however), with a more pronounced stripe
of 50+% probabilities for more than 4 inches on D2 across this same
area and extending into WI and lower MI. The transient nature of
the system will limit the high-end snowfall, but some areas locally may
receive around 8 inches of snowfall.

Additionally, south of this axis of heaviest snow, a transition
zone of mixed precipitation, including freezing rain is expected,
leading to at least modest ice accretion. While light freezing rain
is expected from far eastern MT through lower MI, the greatest
chance (10-30%) for more than 0.1" of icing exists across eastern
ND and western MN.

As this storm exits the Great Lakes and moves into Ontario D3, the
downstream strong WAA will overrun a very cold antecedent airmass.
This will create a broadening plume of wintry precipitation,
falling primarily as snow from Upstate NY through northern New
England, with some mixing, including periods of freezing rain,
expected farther south into the northern Mid-Atlantic and southern
New England. Total accumulations of wintry precipitation should be
less than areas upstream, but WPC probabilities early D2 into D3
for 4+ inches of snow reach 50-90% for portions of western PA and
across the southern Adirondacks, Greens, Whites, and terrain of
northern ME.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes and into the Central Appalachians. While some
of this snow will fall on top of the synoptic snow noted above
(and is included in the snowfall probabilities), and additional 4+
inches of snow has a moderate risk of occurring across the Chautauqua
Ridge from D2 into D3. Similar probabilities for 4+ inches of snow exist
in the higher terrain of WV as well where upslope flow and gusty winds
could create hazardous impacts. The Tug Hill Plateau, in
particular, has rather high chances (>70%) for snowfall totals
surpassing 8" with even low-to-moderate chances (30-50%) for
snowfall topping 12 inches.


Weiss/Mullinax





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 092030
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
330 PM EST Tue Dec 9 2025

Valid 00Z Wed Dec 10 2025 - 00Z Sat Dec 13 2025


...Pacific Northwest through the Northern High Plains...
Days 1-3...

Atmospheric River (AR) event to continue through the rest of the
week with heavy rain/snow for the Pacific Northwest into/through
the northern Rockies and western High Plains.

The strong AR will continue this evening/overnight over the
Cascades and push high snow levels into the region from the
southwest, initially from 4000-5000ft over northern WA but rising
to over 7000- 9000ft by early Wednesday as the jet lifts northward
across British Columbia. Any snow at the higher passes will change
to rain even into the higher terrain of NW MT tomorrow with the
strong IVT push (exceeding the 99.5th percentile) as snow levels
rise to 7000ft. Farther southeast, mid-level shortwave will help
yield snow to the higher terrain of WY as well through Wednesday.
For Day 1, WPC probabilities for at least 8 inches of snow are >50%
above 5000- 6000ft over northern areas and above 8000-9000ft over
WY into northern CO.

Into Day 2, upper jet will wobble a bit across southern BC but
keep the Northwest in mild conditions with snow levels 7000-9000ft
to start. Through the day Thursday, ridging over the Northeastern
Pacific may allow snow levels to slip a bit, especially by Thursday
evening as the intense moisture plume subsides a bit. WPC
probabilities for at least 8 inches of snow are >50% above about
6000ft. Much colder air will dive southward east of the Divide
across Montana setting up a significant snowfall by Friday.

By Day 3, ridging will establish itself on a NNW axis from NorCal
into the Northeast Pacific, allowing the moisture plume to lift
northward through BC and also dig southward along/east of the
Divide across much of Montana. At the same time, the strong cold
front will have brought in much colder air to most of the state
east of the Divide, coincident with cold Canadian high pressure
from the north. With a continued moisture surge (albeit less than
earlier in the period but still a quite respectable >90th
percentile PW and IVT), snow will expand and strengthen over
central/eastern MT as snow ratios rise as well. Strong low/mid-
level FGEN may support a heavier axis of snow from central to
southeastern MT but there remains disagreement on the placement as
the upper jet meanders over northeastern MT. For just Day 3 through
00Z Sat, WPC probabilities for at least 6 inches of snow are
highest in areas above 6000ft in the northern Rockies. Over central
to eastern/southeastern MT, WPC probabilities for at least 6
inches of snow are >50% from just east of Great Falls southeastward
through Billings to near the WY border. Snow will continue past
this period as well.


...Upper Midwest through the Great Lakes and Northeast...
Days 1-3...

An amplified shortwave and accompanying vorticity lobe will
quickly dive from the Upper Midwest to across the southern Great
Lakes and into the Northeast through Thursday morning. The
impressive height falls ahead of this wave will overlap efficiently
with the LFQ of a stout Pacific jet streak, producing intense deep
layer lift which will help deepen the resulting surface low. This
surface low / Alberta Clipper will scoot across lower Michigan by
Wednesday morning and northern Maine/Quebec by Thursday morning.
Above normal moisture in conjunction with the impressive dynamics
will lead to a swath of moderate to heavy snowfall along the
surface low track. WPC probabilities for snowfall >4" remains
moderate to high (45-75%) across the heart of WI and central Lower
Michigan, with low probabilities (10-30%) of snowfall >6". South of
the axis of snowfall, a stripe of freezing rain is possible across
portions of southeast MN, northeast IA, southern WI, northern IL,
southern MI, northeast IN and northwest OH, though any ice
accretions will be less than a tenth of an inch.

As this clipper system moves from the Upper Midwest and Great
Lakes and into the Northeast, the downstream strong WAA will
overrun a very cold antecedent airmass. This will create a
broadening plume of wintry precipitation, falling primarily as snow
from Upstate NY through northern New England, with some mixing,
including periods of freezing rain, expected farther south into the
northern Mid- Atlantic and southern New England. Total
accumulations of wintry precipitation should be less than areas
upstream, but WPC probabilities Day 1 into Day 2 for 4+ inches of
snow reach 60-95% for portions of western PA and across the
southern Adirondacks, Greens, Whites, and terrain of northern ME.
Meanwhile, WPC probabilities for freezing rain >0.01" are low to
moderate (30-60%) for the higher terrain of northeast PA and
northwest NJ.

Finally, behind this system a brief period of favorable NW flow
will create lake effect snow (LES) and upslope snow across the
eastern Great Lakes through Day 3. While some of this snow will
fall on top of the synoptic snow noted above (and is included in
the snowfall probabilities), an additional 4+ inches of snow has
moderate to high probabilities (50-95%) downwind of Lake Erie and
especially Lake Ontario. The Tug Hill Plateau, in particular, has
rather high chances (>70%) for snowfall totals surpassing 8" with
even low-to-moderate chances (30-60%) for snowfall topping 12
inches.


...Midwest and Lower Ohio Valley to the Central Appalachians...
Day 3...

A vigorous Clipper system (mid level vort lobe) across the Midwest
Friday morning will pivot through the Lower OH Valley and into the
WV Mountains Friday afternoon and early evening. Overall the model
QPFs (at least the blended means) have come up at 12Z, though
latitudinal differences remain (not surprising given a day 3
forecast). WPC deterministic QPF incorporated a PMM of the latest GFS/ECMWF/NAM/RRFS, which yields a rather elongated footprint of
0.25-0.35" liquid QPF from north-central IL east-southeast through
central IN, southern OH, far northern KY, and essentially the
middle 2/3rds of WV.

Highest QPFs (0.50+ liquid) again were noted across the most
elevated windward slopes in WV, where the westerly upslope is most
favorable. This is also where the latest WPC probabilities of at
least 4" in 24hrs are highest -- currently between 50-70+ percent.
Elsewhere across north-central IL into central portions of IND,
spotty 4"/24hr probabilities between 30-60% were noted.


Fracasso/Miller/Hurley

$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 100825
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Wed Dec 10 2025

Valid 12Z Wed Dec 10 2025 - 12Z Sat Dec 13 2025


...Pacific Northwest through the Northern High Plains...
Days 1-3...

The atmospheric river (AR) plaguing the Pacific Northwest with
copious amounts of rainfall continues today and into Thursday with
anomalous Pacific moisture coupled with >90th climatological
percentile winds within the 700-200mb layer over WA, northern ID,
and much of MT. Snow levels will be on the rise today, reaching
anywhere from 7,000-9,000ft as the 500-200mb jet core drifts north.
This should begin to force most passes to changeover to rain,
while any lingering snow occurs in the more remote areas of the
Cascades and Lewis Range. The only notable area for heavy snowfall
today is along the >9,000ft peaks of the Absaroka, Tetons, Big
Horns, and Wind River ranges of southern MT and western/northern
WY. WPC probabilities show moderate-to-high chanceS (50-70%) for
snowfall totals >8" through Wednesday night.

Focus turns to Thursday as an Alberta Clipper tracking across
eastern MT helps to usher in an Arctic front from southern Canada.
As the Arctic high builds in from the north, low-level easterlies
will upslope into central and western MT at the same time a ribbon
of 700-300mb moisture streams in overhead. 700mb WAA within W-NW
flow will encounter the Arctic air-mass and result in a band of
700mb FGEN over central MT by Thursday night, resulting in a
quasi-stationary zone of heavy snow over the heart of Big Sky
Country. Heavy snow will linger over the heart of MT through Friday
afternoon before drifting east into eastern MT and the western
Dakotas Friday night. As the band advances east, downsloping winds
and a drying within the 800-500mb layer could cause precipitation
to change over to a wintry mix in central MT, potentially
resulting in a glaze of ice atop fresh snow Friday night.

WPC probabilities moderate-to-high chances (50-80%) for snowfall
totals >8" in central MT with even some low-chance probabilities
10-30%) for isolated totals surpassing 18". The Lewis Range above
5,000ft are likely to receive anywhere between 12-24" of snowfall,
with the remote reaches of the Big Snowy and Little Belt Mountains
potentially exceeding 24". The WSSI-P Moderate probabilities in
central MT are >50% in central and south-central MT, with
Interstates 90, 94, and 87 all at risk of seeing hazardous travel
conditions, with some potential for considerable disruptions and
closures as well. This is depicted in the WSSI-P as well,
indicating 10-20% chances for Major Impacts along portions of these
Interstates Friday and into Saturday morning.


...Great Lakes & Northeast...
Days 1-3...

A shortwave trough responsible for the heavy snow across portions
of the Upper Midwest will strengthen as it tracks through the OH
Valley today. As it does, strong WAA out ahead of the trough will
work in tandem with the left-exit region of a 250-500mb mean
layered left-exit region over the Northeast to produce widespread
precipitation today from the central Appalachians to New England.
An exceptionally cold/dry antecedent air-mass by early December
standards will keep wet-bulb temperatures cold enough to support
snow at the onset across northern PA, the Catskills, Tug Hill,
Adirondacks, Berkshires, and the rest of the New England mountains
through Wednesday afternoon. Farther south, central and eastern
PA, as well as northwest NJ, are likely to see an icy wintry mix
this morning that could result in slick roads, particularly after
following a couple very chilly days where surfaces have been
steadily below freezing. From this "front-end thump" of WAA-driven
and some upslope enhanced snowfall, snowfall totals are likely to
range mostly between 1-4" with the higher totals confined to the
Tug Hill, Adirondacks, Berkshires, Green, and White Mountains where
WPC probabilities show high chances (>70%) for snowfall totals >6"
through Wednesday night.

As low pressure tracks into the St. Lawrence Valley tonight, CAA
within cyclonic flow on the backside of the storm will kick-start
the Lake Effect Snow (LES) machine, as well as supply the central
Appalachians with pronounced upslope snowfall. Precipitation will
fall as snow across the Central Appalachians with lowering snow
levels throughout the day Wednesday and impressive 40-50 kts winds
at 850mb will mix down to cause strong winds within increasing
snowfall rates. This will result in dangerous travel conditions in
the Central Appalachians with whiteout conditions expected above
2,000ft. Snow and winds should gradually taper off Thursday
morning. WPC probabilities show moderate-to-high chances (50-70%)
for snowfall totals >6" with localized low-chance probabilities
(10-30%) for amounts >12". Elsewhere, the LES belts over the
eastern Michigan U.P., northwest section of Michigan's Mitten,
along the Chautauqua Ride, and down wind of Lake Ontario will see
LES bands that stick around these areas through Thursday, with the
band off of Lake Ontario lingering into Friday as well. Through
Friday morning, the Tug Hill Plateau sports high chances (>70%) for
snowfall totals topping 12", with moderate-to-high chances (40-70%)
for >12" amounts along the Chautauqua Ridge through Friday
morning.


...Northern Plains, Midwest, Lower Ohio Valley, & Central
Appalachians...
Days 2-3...

A potent clipper emerging from eastern MT Thursday morning will
race southeast into the heart of the Midwest by Thursday evening.
Healthy 850mb WAA and FGEN to the north and east of the low track
will cause a narrow band of snow light-to-moderate snow from the
eastern Dakotas and southern MN to the nose of IA, and in some
cases a wintry mix across the northern High Plains. The 850mb
FGEN/WAA pivots over the Lower Ohio Valley Thursday night and
reaches the Central Appalachians by early Friday morning. WPC
probabilities show generally lw-to-moderate chances (20-50%) for

4" of snow from central MN on south and east across northern IL,

south-central IN, and southern OH. The highest probabilistic
chances for >4" of snowfall resides in the Potomac Highlands and
central Appalachians of eastern WV and western MD. Here, WNWrly
upslope winds within a 290K isentropic regime and higher SLRs will
provide a favorable environment for locally heavy snowfall. WPC
probabilities show most of the Potomac Highland and central
Appalachians in eastern WV and western MD have moderate-to-high
chances (50-70%) for snowfall totals >4", with some guidance
indicating low chances (10-30%) for localized totals surpassing
10".

There are some members of guidance that depict a chance for light
snowfall across the Mid-Atlantic on Friday, particularly the Blue
Ridge of VA/WV and potentially in the northern VA/northern
MD/southern PA. ECMWF and GFS show weak 700mb Q-vector convergence
over the region with just enough 700-300mb layer saturation to
support a chance for light snow. WPC probabilities show low chances
(10-30%) for >1" snowfall totals across southern and central PA,
northern MD, and northwest VA. While referencing >1" snowfall
potential may seem trivial to mention, recent Mid-Atlantic
snowfall events over the past week has seen snowier trends inside
of 60 hours. It is worth monitoring, but overall snowfall and
travel disruption potential at this time would be light. The WSSI-P
does show 10-20% odds for Minor Impacts across portions of northern
VA and northern MD on Friday.


Mullinax




$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105)

FOUS11 KWBC 102035
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 PM EST Wed Dec 10 2025

Valid 00Z Thu Dec 11 2025 - 00Z Sun Dec 14 2025


...Pacific Northwest through the Northern High Plains..
Days 1-3...

The strong Atmospheric River (AR) will start to wane over the
Cascades tonight with the last push of moisture onto the coast. The
upper jet will wobble a bit across southern BC but keep the
Northwest in mild conditions with snow levels 7000-9000ft to start
this evening. Through the day tomorrow, increased ridging over the
Northeastern Pacific will allow snow levels to slip a bit,
especially by Thursday evening as the precipitation intensity
decreases. WPC probabilities for at least 8 inches of snow are >50%
above about 5500ft. Much colder air will dive southward east of the
Divide across Montana setting up a significant snowfall by Friday.

Over the High Plains, warm advection atop a cold surface boundary
layer will support freezing rain from northeastern MT southeastward
through southwestern ND into central SD on Thursday. Model QPF
placement/axis and amounts continue to vary across the region but
trended up with the latest cycle. This introduced some moderate
probabilities (30-60%) of at least 0.10" of icing over north central
SD and northeastern MT/southwestern ND.

By Day 2, ridging will push the moisture plume into British Columbia
but also allow a strong surface cold front to rush southward east of
the Divide. With a continued moisture surge up and around the Pac NW
(albeit less than earlier in the period but still a quite
respectable >90th percentile PW and IVT), snow will expand and
strengthen over central/eastern MT as snow ratios rise as well.
Strong low/mid-level FGEN may support a heavier axis of snow from
central to southeastern MT. Snow will continue into Saturday but
lift northward as the jet wobbles back to the northeast, pushing the
snow into northeastern MT. By Saturday afternoon upper ridging will
finally push inland into the Northwest, yielding drier conditions
for the region. For the day 2-3 period, WPC probabilities of at
least 4 inches of snow are >50% over a large area of Montana east of
the Divide, from just east of Cut Bank through Havre, southward to
Billings, and eastward to southeastern MT/northwestern SD. Within
this region, WPC probabilities for at least 8 inches of snow are

40% across central MT between Havre and Billings.

...Central Appalachians & Northeast...
Day 1...

As low pressure tracks into the St. Lawrence Valley tonight into
Thursday, the focus will shift from synoptically driven snowfall
across northern New England and interior portions of the Northeast
to lake effect snowfall downwind of the Great Lakes. Prior to this
transition, additional snowfall will be most notable across the
Adirondacks, Berkshires, Green, and White Mountains where WPC
probabilities for >6" are moderate to high (60-90%). Additionally, strengthening northwesterly winds oriented perpendicular to the
central Appalachians will also result in significant upslope
snowfall through tonight and into Thursday morning. WPC
probabilities for >4" of snow is moderate to high (50-90%) across
portions of the higher terrain of WV and far western MD with
similar chances for >6".


...Great Lakes...
Days 1-3...

Cold advection within cyclonic flow around the storm system
exiting the Northeast will result in several lake effect snow bands
which are likely to produce multiple rounds of moderate to heavy
snow the next few days. The most prominent bands will develop and
persist along the Chautauqua Ride and across the Tug Hill through
Thursday, with the band off of Lake Ontario lingering into Friday
as well. Lesser bands will also affect the eastern Michigan U.P.
and the northwest section of Michigan's Mitten with WPC
probabilities of total snowfall >4" of 30-70% through Friday.
Meanwhile, the Tug Hill Plateau sports high chances (>70%) for
snowfall totals topping 8", with low to moderate chances (30-60%)
for >12" amounts. Moderate to high chances (40-80%) of >8" also
remain along the Chautauqua Ridge through Friday as well.

By Day 3, a renewed shot of CAA associated with a sharpening trough
and embedded vort max will support additional bands of lake effect
snow downwind of all the Great Lakes, but especially across
portions of the eastern U.P. of Michigan and the northwest portion
of lower Michigan. Here, WPC probabilities for snowfall >4"
increase to 50-90%, with 20-50% probabilities of >8" even outlined
across a small portion of the U.P of Michigan. Low to moderate
probabilities of additional snowfall >4" are also highlighted
downwind of Lake Erie and Lake Ontario.


...Midwest, Ohio Valley, & Central Appalachians...
Day 2...

Emanating from the Northern Rockies/High Plains system, northwest
flow will support a clipper system from the Midwest through the Ohio
Valley into the central Appalachians Thursday afternoon into Friday.
Models continued to struggle with the QPF axis (varying a couple
hundred miles northeast to southwest), with a preference toward the
global and AI models vs the hi-res models. Sufficient moisture
combined with modest forcing beneath the 140kt jet streaks and
within/along a low-level thermal gradient should yield several
inches of snow where SLRs are >12:1. Day 2 WPC probabilities of at
least 4 inches of snow are >30% along an axis from central IL to northern/northeastern KY.


...Corn Belt to the Midwest...
Day 3...

Broad cyclonic flow over Hudson Bay/eastern Canada will carry
another shortwave around its southwestern periphery Friday night
into Saturday from the Plains through the Corn Belt to the Midwest.
This will yield yet another chance of light snow for the region on
the heels of the previous system. WPC probabilities for at least 4
inches of snow on Day 3 are low for now, generally 10-30%, from Iowa
through central IL.


Fracasso/Miller/Mullinax


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 110840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Thu Dec 11 2025

Valid 12Z Thu Dec 11 2025 - 12Z Sun Dec 14 2025


...Montana...
Days 1-2...

A swath of heavy snowfall is likely tonight into Friday across
much of central and eastern MT. A strong cold front will drop
south today in response to a building mid level ridge off the West
Coast. While considerably weaker than prior days, IVT is still
forecast over the 97th percentile over MT, with PWs around the 90th
percentile. This moisture will override the cold front and result
in a swath of significant snowfall. The latest WPC probabilities
indicate a high chance (greater than 80%) of >4" of snow over much
of central and eastern MT, with portions of the area likely to
exceed 8". This is expected to be more of a prolonged moderate
snowfall with the event picking up in intensity later tonight and
ending late Friday night...although periods of more intense
snowfall rates are likely.

...Great Lakes into Northeast...
Days 1-3...

Cold advection within cyclonic flow around the storm system
exiting the Northeast will result in several lake effect snow bands
today. The most prominent bands will be over the Chautauqua Ridge
and off of Lake Ontario towards Syracuse. WPC probabilities give
both of these areas a greater than 70% chance of an additional 4"+
of snow today into tonight.

On Friday a weak area of low pressure will bring an initial batch
of light WAA snow to the Great lakes, followed by CAA lake effect
snow in its wake. WPC probabilities of exceeding 6" of snow with
this event are over 50% across the lakeshore of the U.P. of
Michigan, northwest lower MI, and the favored areas downwind of
Lake Erie and Ontario. While some areas may locally exceed 8", this
is not expected to be a high end lake effect event given the
relatively short duration of the most favorable ingredients.


...Dakotas, Midwest, Ohio Valley, & Central Appalachians...
Days 1-2...

Northwest flow will support a clipper system moving from the
Northern PLains into the OH Valley today into Friday morning
resulting in a swath of light to moderate snowfall amounts.
Initially we should see a swath of freezing rain this morning from
portions of south central ND into central SD just north of the
shallow cold front, with the latest WPC forecast supporting some
ice accumulations of around or even a bit higher than 0.10".
However as the system quickly moves east today the main
precipitation type will be snow, with perhaps just a bit of a mix
and/or rain on the far southern extent of the precipitation shield.

Even at this short lead time there remains some uncertainty with
the exact axis of highest snowfall with this system. The 00z high
res models remain north of the global guidance, but they did trend
south compared to their 12z runs. The latest WPC preference takes
a consensus approach, resulting in a swath a bit south of the 00z
HREF mean, and a tad north of the global model consensus. The quick
movement of this system will limit snowfall magnitudes, although
the latest WPC probabilities depict a swath of a 30-50% chance of

4" of snow from portions of central IL into south central IN and

towards the KY border. These probabilities could be a bit low, with
these quick hitting clipper systems often verifying with a narrow
band of higher amounts, and a good amount of this snow falling
overnight helping with accumulations. Thus would expect to see a
swath of 4-5" with this system, with a few totals over 5" possible.

The system will begin to weaken as it moves into the Mid-Atlantic,
and thus not expecting much in the way of snow to make it east of
the Appalachians. Even with the weakening nature of the system,
upslope flow will still support accumulating snow over the favored
terrain of WV into southwest VA, with >4" snow probabilities
peaking in the 30-50% range over southeast WV Friday.


...Corn Belt, Midwest, Ohio Valley and Mid-Atlantic...
Day 3...

Another quick moving system will eject into the Northern Plains
Friday night into Saturday, quickly moving across the OH Valley on
Saturday and into the Mid-Atlantic Saturday night into Sunday
morning. This will be a quick moving system which will limit
snowfall magnitudes, however widespread minor impacts can be
expected, with WPC probabilities already indicating a 60-80%
chance of >2" of snow from SD into OH. The probabilities of >4"
drop into the 10-40% range...indicating that totals of this
magnitude are currently unlikely to be widespread, but may very
well occur in localized swaths along the track.

As this system approaches the Appalachians the mid level trough
begins to dig and take on more of a neutral tilt. This will
increase mid and upper level southerly flow and begin the process
of coastal low development. Most likely this trough will remain
too progressive and take on a negative tilt too late to bring a
significant snowfall risk to the Mi-Atanltic and Northeast.
However, it is becoming increasingly likely that we see enough
increase in forcing to see an expansion of some accumulating snow
into the Mid-Atlantic Saturday night.

This expected evolution will support a more prolonged period of
accumulating snowfall into portions of WV and southwest PA, where
probabilities of >4" of snow have increased into the 50-80% range,
with >6" probabilities even over 40%. By later Saturday night model
guidance is trending towards a more favorable solution for a quick
shot of snow even into coastal areas of the Mid-Atlantic. In fact
the 00z deterministic GFS/CMC/ECMWF/AIFS would all bring some
accumulation of snow into the DC to NYC corridor. From an ensemble
perspective, the WSSI-P shows a 50-60% chance of minor impacts
from DC to NYC and a 10-20% chance of Moderate impacts. This
generally seems like a 1-3" event, but the latest guidance does
support the potential for a narrow axis of 3-5" somewhere over the
eastern Mid-Atlantic. This is a lower probability outcome and
likely the ceiling for this event given the quick storm motion, but
the risk is supported by the aforementioned low WSSI-P moderate
probabilities and some low >4"+ WPC probabilities. These quick
northwest flow systems are tricky to pin down with much lead time,
so future adjustments to the forecast are likely.

Chenard


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 111951
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 PM EST Thu Dec 11 2025

Valid 00Z Fri Dec 12 2025 - 00Z Mon Dec 15 2025


...Montana...
Days 1-2...

A second round of heavy snowfall (although with minimal break from
the first) will develop across MT, generally east of the
Continental Divide and expand into the High Plains. This will be
the result of overlapping ascent slowly shifting northeast with
time into a cold and anomalously moist environment.

The event begins to expand as a powerful (150+ kt) Pacific jet
streak begins to pivot northeast, while a strong cold front
continues to waver NW to SE and bank into the terrain. The overlap
of this jet and its accompanying IVT (still > 90% probability of
exceeding 250 kg/m/s spilling east of the terrain) will help expand precipitation once again across the area. This will fall
exclusively as snow thanks to rapid column cooling behind the
front. The accompanying westerly flow aloft, while not ideal for
column moistening, will lead to at least modest isentropic ascent
atop the cold front, primarily along the 290K-295K surfaces,
helping to expand the snow swath. At the same time, persistent
700-600mb fgen will drift across the area, aided by the entrance
region to the upper jet, and driving ascent efficiently into the
deepening DGZ (30% probability from the SREF for DGZ depth
exceeding 100mb) suggest the potential for periods of heavy
snowfall rates exceeding 1"/hr (up to 70% chance Friday evening).

Temperatures will be quite cold, so SLRs are expected to be fluffy
and above-climo which should result in rapid accumulation of
snowfall. This will be most pronounced where any jet-enhanced
banding can occur, especially due to the prolonged and nearly-
stationary nature of the upper jet aloft. This is reflected by WPC probabilities that support a moderate risk (50-90%) for at least 6
inches of snow across central MT just east of the terrain, with
locally as much as 12" possible (10-30%), and locally higher
amounts in the mountains.


...Great Lakes into Northeast...
Days 1-3...

Persistent troughing across the east will keep cyclonic flow in
place across the Great Lakes and into the Northeast through the
weekend, while periodic shortwave impulses rotate southeast through
the flow. Each of these shortwaves will result in transient
enhanced ascent, with the most impressive height falls likely D3 as
the last in this series of shortwaves amplifies sharply late in the
forecast period.

The result of this evolution will be periods of light synoptic snow
associated with each shortwave, followed by more impressive lake
effect snow (LES) or lake-enhanced snow. While many areas will
likely experience at least light synoptic snow, any significant
accumulations are expected to be confined to lake effect snow areas
on the persistent W/NW flow, with enhancement occurring behind
each shortwave and the accompanying CAA. On D1, modest LES, which
has a WPC probability of 10-30% for exceeding 4" is confined to the
Keweenaw Peninsula of MI and just east of Lake Ontario.

However, during D2 and D3, LES becomes more widespread and
intense. With 850mb temps crashing to potentially less than -20C
over the lake temperatures that are still generally +2C to +8C will
create deep inversion depths and impressive lake-induced
instability to support heavy LES. Snowfall rates of at least 2"/hr
appear probable, especially across the U.P. and then east of Lakes
Erie/Ontario where upstream connection may additionally occur. WPC probabilities D2 for 4+ inches of snow are above 50% across much of
the southern shore of Lake Superior in the U.P., as well as near
Buffalo, NY and into the Tug Hill Plateau. By D3, these
probabilities expand to include the NW and SW L.P. of MI as well as
the breadth of the Chautauqua Ridge. 2-day snowfall totals from the
LES (D2-D3) could 18" in some areas.

...Northern Plains through the Ohio Valley...
Days 1-3...

Pinched cyclonic flow on the periphery of an amplifying trough over
southeast Canada will keep flow progressive from the Northern
Plains through the Ohio Valley, while dual potent shortwave troughs
rotate through the flow.

The first of these will be accompanied by a strung out lobe of
vorticity racing from South Dakota early D1 to the Mid-Atlantic
Coast early D2. The speed of this system will somewhat limit the
potential for heavy precipitation. However, forcing for ascent will
maximize on the periphery of a potent upper jet streak digging
southeast coincident with a narrow corridor of impressive 290K
isentropic ascent and 925-700mb fgen. The most intense ascent is
expected from Iowa into Kentucky where a band of heavy snowfall is
likely to translate southeast on the edge of the strongest WAA.
This will create a stripe of moderate snowfall with briefly heavy
snow rates exceeding 1"/hr possible (30% chance). WPC probabilities
for this lead shortwave reach 30-50% for 4+ inches, with locally
6+" possible (10-30%) in IL/IN.

Immediately following this first wave will be a second shortwave
with more impressive amplitude, leading to a second streak of
moderate to heavy snowfall crossing almost the identical path.
Although there is considerable latitudinal spread among the
guidance, it is probable that the lead shortwave will push the
baroclinic gradient south to support a slight southward push of
heavy snow with the next wave, at least until amplification of the
mid-level pattern occurs Saturday evening which could result in the
heaviest axis again moving across central IN and then into the
lower Ohio Valley. Another stripe of moderate to heavy snow is
likely despite the transient nature of the event as the DGZ remains
elevated and 700-600mb fgen increases which crosses directly into
the DGZ to produce ample snow growth potential. Regional soundings
across this area also indicate a near-isothermal layer beneath the
DGZ, and while temperatures are cold, should still support fluffy
SLR with efficient accumulations. At this time, WPC probabilities
on D2 indicate a 30-50% chance of an additional 4+ inches in
central IL, reaching 30-70% D3 from IN through southern OH.

Although there will be a break between these two events, some areas
could receive double-digit snowfall by the time both of these
events are over, and with cold temperatures in place, this will
likely create hazardous travel for the region.


...Central Appalachians and Mid-Atlantic...
Days 1-3...

The same impulses/clippers bringing snow to the Plains/Midwest will
track E/SE into the Central Appalachians and Mid-Atlantic states.
The first of these will be exiting the coast Friday morning, and
while snow will generally be modest, the addition of upslope flow
on W/NW winds into the Central Appalachians will result in moderate accumulations across the terrain of WV. Here, WPC probabilities D1
into D2 support a low risk (10-30+%) of at least 4 inches of
snowfall.

The more significant event is with the secondary impulse which will
be intensifying D3 as the mid-level pattern amplifies and swings
the primary trough axis into the Central Appalachians and Mid-
Atlantic Sunday morning. This will drive rapid height falls into
the area, while the sharpening trough axis will help arc the
downstream jet streak poleward to produce rapidly intensifying
upper diffluence within the RRQ. Westerly mid-level flow will cause
impressive upslope flow into the terrain of WV/MD/PA once again,
but in this cause the available moisture will be more significant,
which when added to the robust deep layer ascent results in WPC
probabilities that exceed 50% for 6+ inches from the Laurel
Highlands through central WV, with locally more than 10 inches
possible.

The more challenging aspect of this forecast is what happens across
the coastal Mid-Atlantic states, including the I-95 corridor. As
the upper jet intensifies and arcs, it will likely provide enough
ascent downstream of the sharpening trough to produce a secondary
axis of moderate to heavy snow in the vicinity of I-95. The speed
at which this trough deepens and the corresponding jet amplifies
will drive the position of the heavy snow axis, which remains quite
uncertain at this time. However, with the PV anomaly swinging east
and potentially pushing the 1.5 PVU surface down below 450mb, this
could be a briefly intense event downstream.

Evaluation of the recent cluster analysis indicates that the
primary EOF /uncertainty/ revolves around the speed of this trough amplification, and there is quite a bit of spread among the various
clusters. In general, the EC members are bit slower and deeper,
while the GEFS members are a little faster and weaker. Somewhere in
the middle is probably reasonable at this time, which results in a
stripe of heavy snow that will develop within increasing 850-700mb
fgen somewhere near I-95 from Washington, D.C. through NYC and
into Cape Cod, MA. There is still a lot of spread, but where this
band develops, which is currently expected near I-95, WPC
probabilities are moderate (50-70%) for at least 2 inches of snow
between DC and NYC, with locally more than 4 inches possible.
Considerable adjustments to the location of this band are still
possible, so further refinements to the location and accompanying
probabilities can be expected in the next few forecast cycles.

Weiss


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 112224
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
524 PM EST Thu Dec 11 2025

Valid 00Z Fri Dec 12 2025 - 00Z Mon Dec 15 2025


...Montana...
Days 1-2...

A second round of heavy snowfall (although with minimal break from
the first) will develop across MT, generally east of the
Continental Divide and expand into the High Plains. This will be
the result of overlapping ascent slowly shifting northeast with
time into a cold and anomalously moist environment.

The event begins to expand as a powerful (150+ kt) Pacific jet
streak begins to pivot northeast, while a strong cold front
continues to waver NW to SE and bank into the terrain. The overlap
of this jet and its accompanying IVT (still > 90% probability of
exceeding 250 kg/m/s spilling east of the terrain) will help expand precipitation once again across the area. This will fall
exclusively as snow thanks to rapid column cooling behind the
front. The accompanying westerly flow aloft, while not ideal for
column moistening, will lead to at least modest isentropic ascent
atop the cold front, primarily along the 290K-295K surfaces,=20
helping to expand the snow swath. At the same time, persistent
700-600mb fgen will drift across the area, aided by the entrance
region to the upper jet, and driving ascent efficiently into the
deepening DGZ (30% probability from the SREF for DGZ depth=20
exceeding 100mb) suggest the potential for periods of heavy=20
snowfall rates exceeding 1"/hr (up to 70% chance Friday evening).=20

Temperatures will be quite cold, so SLRs are expected to be fluffy
and above-climo which should result in rapid accumulation of
snowfall. This will be most pronounced where any jet-enhanced
banding can occur, especially due to the prolonged and nearly-
stationary nature of the upper jet aloft. This is reflected by WPC probabilities that support a moderate risk (50-90%) for at least 6
inches of snow across central MT just east of the terrain, with
locally as much as 12" possible (10-30%), and locally higher
amounts in the mountains.


...Great Lakes into Northeast...
Days 1-3...

Persistent troughing across the east will keep cyclonic flow in
place across the Great Lakes and into the Northeast through the
weekend, while periodic shortwave impulses rotate southeast through
the flow. Each of these shortwaves will result in transient
enhanced ascent, with the most impressive height falls likely D3 as
the last in this series of shortwaves amplifies sharply late in the
forecast period.

The result of this evolution will be periods of light synoptic snow
associated with each shortwave, followed by more impressive lake=20
effect snow (LES) or lake-enhanced snow. While many areas will
likely experience at least light synoptic snow, any significant
accumulations are expected to be confined to lake effect snow areas
on the persistent W/NW flow, with enhancement occurring behind
each shortwave and the accompanying CAA. On D1, modest LES, which
has a WPC probability of 10-30% for exceeding 4" is confined to the
Keweenaw Peninsula of MI and just east of Lake Ontario.=20

However, during D2 and D3, LES becomes more widespread and=20
intense. With 850mb temps crashing to potentially less than -20C
over the lake temperatures that are still generally +2C to +8C will
create deep inversion depths and impressive lake-induced
instability to support heavy LES. Snowfall rates of at least 2"/hr
appear probable, especially across the U.P. and then east of Lakes
Erie/Ontario where upstream connection may additionally occur. WPC probabilities D2 for 4+ inches of snow are above 50% across much of
the southern shore of Lake Superior in the U.P., as well as near
Buffalo, NY and into the Tug Hill Plateau. By D3, these
probabilities expand to include the NW and SW L.P. of MI as well as
the breadth of the Chautauqua Ridge. 2-day snowfall totals from the
LES (D2-D3) could 18" in some areas.


...Northern Plains through the Ohio Valley...=20
Days 1-3...

Pinched cyclonic flow on the periphery of an amplifying trough over
southeast Canada will keep flow progressive from the Northern
Plains through the Ohio Valley, while dual potent shortwave troughs
rotate through the flow.=20

The first of these will be accompanied by a strung out lobe of
vorticity racing from South Dakota early D1 to the Mid-Atlantic
Coast early D2. The speed of this system will somewhat limit the
potential for heavy precipitation. However, forcing for ascent will
maximize on the periphery of a potent upper jet streak digging
southeast coincident with a narrow corridor of impressive 290K
isentropic ascent and 925-700mb fgen. The most intense ascent is
expected from Iowa into Kentucky where a band of heavy snowfall is
likely to translate southeast on the edge of the strongest WAA.
This will create a stripe of moderate snowfall with briefly heavy
snow rates exceeding 1"/hr possible (30% chance). WPC probabilities
for this lead shortwave reach 30-50% for 4+ inches, with locally
6+" possible (10-30%) in IL/IN.

Immediately following this first wave will be a second shortwave
with more impressive amplitude, leading to a second streak of
moderate to heavy snowfall crossing almost the identical path.
Although there is considerable latitudinal spread among the
guidance, it is probable that the lead shortwave will push the
baroclinic gradient south to support a slight southward push of
heavy snow with the next wave, at least until amplification of the
mid-level pattern occurs Saturday evening which could result in the
heaviest axis again moving across central IN and then into the
lower Ohio Valley. Another stripe of moderate to heavy snow is
likely despite the transient nature of the event as the DGZ remains
elevated and 700-600mb fgen increases which crosses directly into
the DGZ to produce ample snow growth potential. Regional soundings
across this area also indicate a near-isothermal layer beneath the
DGZ, and while temperatures are cold, should still support fluffy
SLR with efficient accumulations. At this time, WPC probabilities
on D2 indicate a 30-50% chance of an additional 4+ inches in
central IL, reaching 30-70% D3 from IN through southern OH.=20

Although there will be a break between these two events, some areas
could receive double-digit snowfall by the time both of these
events are over, and with cold temperatures in place, this will
likely create hazardous travel for the region.


...Central Appalachians and Mid-Atlantic...
Days 1-3...

The same impulses/clippers bringing snow to the Plains/Midwest will
track E/SE into the Central Appalachians and Mid-Atlantic states.
The first of these will be exiting the coast Friday morning, and
while snow will generally be modest, the addition of upslope flow
on W/NW winds into the Central Appalachians will result in moderate accumulations across the terrain of WV. Here, WPC probabilities D1
into D2 support a low risk (10-30+%) of at least 4 inches of
snowfall.

The more significant event is with the secondary impulse which will
be intensifying D3 as the mid-level pattern amplifies and swings
the primary trough axis into the Central Appalachians and Mid-
Atlantic Sunday morning. This will drive rapid height falls into=20
the area, while the sharpening trough axis will help arc the
downstream jet streak poleward to produce rapidly intensifying
upper diffluence within the RRQ. Westerly mid-level flow will cause
impressive upslope flow into the terrain of WV/MD/PA once again,
but in this cause the available moisture will be more significant,
which when added to the robust deep layer ascent results in WPC
probabilities that exceed 50% for 6+ inches from the Laurel
Highlands through central WV, with locally more than 10 inches
possible.

The more challenging aspect of this forecast is what happens across
the coastal Mid-Atlantic states, including the I-95 corridor. As
the upper jet intensifies and arcs, it will likely provide enough
ascent downstream of the sharpening trough to produce a secondary
axis of moderate to heavy snow in the vicinity of I-95. The speed
at which this trough deepens and the corresponding jet amplifies
will drive the position of the heavy snow axis, which remains quite
uncertain at this time. However, with the PV anomaly swinging east
and potentially pushing the 1.5 PVU surface down below 450mb, this
could be a briefly intense event downstream.

Evaluation of the recent cluster analysis indicates that the=20
primary EOF /uncertainty/ revolves around the speed of this trough=20 amplification, and there is quite a bit of spread among the various
clusters. In general, the EC members are bit slower and deeper,=20
while the GEFS members are a little faster and weaker. Somewhere in
the middle is probably reasonable at this time, which results in a
stripe of heavy snow that will develop within increasing 850-700mb
fgen somewhere near I-95 from Washington, D.C. through NYC and=20
into Cape Cod, MA. There is still a lot of spread, but where this=20
band develops, which is currently expected near I-95, WPC
probabilities are moderate (50-70%) for at least 2 inches of snow
between DC and NYC, with locally more than 4 inches possible.
Considerable adjustments to the location of this band are still
possible, so further refinements to the location and accompanying
probabilities can be expected in the next few forecast cycles.

Weiss



...Extreme Cold Messages are in effect. Please see current Key=20
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7oKQMthO_AgvWGJsUC1TmBbPapSWjWECK-1YZ5cN-q80V= kFeTBweceqBKIk5Gax1GIyogCRFY1qpHApLNATHY68k4h0$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 120908
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EST Fri Dec 12 2025

Valid 12Z Fri Dec 12 2025 - 12Z Mon Dec 15 2025


...Montana...
Day 1...

NWly jet downstream of an amplifying ridge axis off the PacNW coast
continues to intensify through this morning with 250mb winds
increasing above 150kt over south-central Alberta. Pacific moisture
continues to shift inland south of this jet which meets
particularly cold air from the Canadian Prairies that is banking=20
up against the eastern slopes of the MT Rockies. The amplifying=20
ridge maintains the jet dynamics with banding over central MT now=20
expected to drift north to northern MT through this evening before=20
ejecting southeast over the north-central Plains late=20
tonight/Saturday morning.=20

Ongoing freezing rain along the southern periphery of the banding
in valleys in the eastern slopes will continue this morning with
only a narrow strip of wintry mix shifting north with the southern
extension rest of today. Otherwise this is fluffy with consistent
0.5"/hr rates across the MT Plains through this evening (per 00Z
HREF) with SLR in the 15 to 18:1 range. Day 1 PWPF for >6" snow is
over 40% across much of north-central to eastern MT, including=20
around Havre where probabilities are above 70%.=20


...Northern Plains through the Midwest to the central=20
Appalachians... Days 1-2...

A reinforcing trough over the Gulf of Alaska early this morning
rides an increasing NWly jet today, reaching southern Saskatchewan
tonight. This trough is the catalyst for allowing ongoing snow
banding over MT to eject southeast across the Dakotas late tonight
and the Midwest Saturday. Strong jet dynamics and ample cold air
with Arctic origin allows for decent snow rates through this swath, consistently over 0.5"/hr per the 00Z HREF. Day 1.5 PWPF for >4"
are lower over South Dakota where the bands are fairly progressive,
generally 30%, but higher over Iowa through north-central IL and
central IN where the band pivots east with values of 40-60%.
Probabilities continue to ramp up to the east over Ohio later
Saturday before orographic lift brings increasing probabilities=20
for >6" to northern WV, peaking for areas just west of the
Allegheny Front where Day 2 PWPF for >6" are 40-70%.=20

This swath is forecast to be a bit north of the current snow
tracking east from southern IN and eastern KY. These two
clippers will produce decent swaths of snow and combine to cover
large areas of the Midwest with snow through Saturday.=20


...Mid-Atlantic through the coastal Northeast...=20
Days 2-3...

The Saturday shortwave trough/clipper amplifies an upper low over
Lake Superior Saturday allowing it to further develop and dig
south over the eastern Great Lakes Saturday night. The surface
component of this low develops as a trough off the Mid-Atlantic
coast to the Outer Banks by 12Z Sunday. Right entrance jet dynamics
and this developing surface trough allow moderate to locally heavy
banding to develop over the central/northern Mid-Atlantic through
southern New England Saturday night into Sunday. Placement of
banding with a key area of 0.25" QPF remains a bit uncertain at
this time, but areas from Baltimore through New Jersey and=20
possible Long Island are of most concern now. Day 2.5 PWPF for >4"=20
are 30-40% around Philly and around 20% over southern Connecticut=20
through southeast Mass. Confidence has increased on the snow=20
advancing and reaching the NYC metro late Saturday evening.=20

Rapid low pressure development is expected off the Northeast coast
Sunday which will maintain offshore flow and should allow ocean/bay
enhanced snow for the Cape and Islands through Sunday night. Day 3
PWPF for >4" are around 30% for Cape Cod.


...Great Lakes...=20
Days 1-3...

Persistent troughing across the east will maintain cold conditions
as a storm brings another round of lake enhanced and effect snow=20
across the Great Lakes tonight through Sunday. Low pressure=20
currently over Manitoba dives southeast to Lake Superior tonight=20
before amplifying by an aforementioned shortwave trough. Westerly=20
flow ahead of this low brings synoptic snow with lake enhancements=20
for the U.P. and tip of the L.P. mitt where Day 1.5 PWPF for >6"=20
are 30-50%.=20

This westerly flow then crosses the eastern Great Lakes early
Saturday bringing renewed cold air advection and transient single-
banding to snow belts east of Cleveland through the Chautauqua
Ridge and across the Tug Hill where Day 2 PWPF for >6" are 40-70%.
LES then continues on NWly flow behind the low on Sunday with Day 3
PWPF for >4" 40-80% in northwest PA and around Syracuse.=20



Jackson



...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!47yZ9O3RTM9AE6Rtm8R9BQEbLvVg3byGcA07p9m73MzIA= 1eUO2G1MfH3v-DCGZA6hRJFaFZPvnR-6NLsfgEM7HTLZE8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 121847
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
147 PM EST Fri Dec 12 2025

Valid 00Z Sat Dec 13 2025 - 00Z Tue Dec 16 2025


...Montana...
Day 1...

The ongoing strong upper jet streak angled NW to SE will continue
tonight and into early Saturday, while westerly mid-level flow
isentropically ascends the baroclinic gradient left from a cold
front banked against the Continental Divide. This will result in=20
persistent moderate snowfall with rates 0.5"/hr to 1"/hr at times=20
across central MT. The heaviest snowfall should taper off quickly=20
late tonight with snow ending by Saturday morning in response to=20
the strongest ascent pivoting east away from the area. The=20
continuing snowfall should remain fluffy with high SLRs thanks to a
very cold column, so additional accumulations exceeding 4 inches=20
are likely (>70% chance) in central MT, with local additional=20
snowfall as much as 8 inches possible (10% chance) in a few areas.


...Northern Plains through the Ohio Valley into the Central=20 Appalachians...=20
Days 1-2...

A closed 500mb low dropping along the Ontario/Great Lakes border
will be the catalyst for another fast moving clipper-type low=20
racing from the Northern Plains to the Ohio Valley D1, and then=20
exiting the Mid-Atlantic coast D2. The primary driver of this=20
clipper is expected to be a secondary impulse/vorticity lobe=20
swinging through the pinched flow, to combine with the persistent=20
and intense upper jet streak aloft driving deep layer ascent. While
the temporal duration of any lift will be modest due to the=20
progressive nature of the system, the overlap of height falls with=20 intensifying fgen (both through WAA and the result of the upper jet
streak position) will be sufficient to drive robust omega through=20
the snow growth zone. With strong lift occurring into a DGZ that is
deepening in the cold airmass, periods of heavy snow are likely,=20
especially within a narrow translating band from eastern SD through
IN on D1, and then continuing into OH D2 before running into the=20
terrain of WV and wringing out the remaining moisture via upslope=20 enhancement before Saturday night.

WPC probabilities for snow exceeding 4" reaches 10-30% from eastern
SD through central IN, but contains a local maxima above 50% in
central IL/IN where the best overlap of ascent into the deepening
DGZ occurs. This could support snowfall rates above 1"/hr at times
leading to local maxima above 6" (10% chance). During D2 the
heaviest snowfall axis shifts eastward, with a 50-90% chance of
more than 4 inches occurring across southern OH and into the
terrain from the Laurel Highlands of PA through central WV. The
greatest snowfall, which may reach 10" in local spots, is expected
in the higher terrain of WV.


...Mid-Atlantic through Southern New England...=20
Day 2...

Extremely challenging forecast for Sunday as a system develops east
of the Mid-Atlantic Sunday morning and then skirts off into the
Atlantic Ocean. The primary mechanism for this system will be the
upstream shortwave racing across the Midwest. As this feature moves
east, it will amplify rapidly into a sharpening trough, but still
maintain a positive tilt. Downstream of this trough, especially 06Z
to 18Z Sunday, rapid height falls will occur through the Mid-
Atlantic states and into southern New England, concurrent with a
rapid amplification of a jet streak which peak above 150 kts in New
England while arcing more poleward. This will place the favorable
RRQ for diffluent ascent directly beneath the strongest height
falls, and the accompanying (albeit modest) fgen due to WAA will
merge with the resulting fgen from the jet streak to drive a period
of rapidly intensifying deep layer ascent. The guidance continues
to suggest that the strongest lift will occur directly into the
DGZ, so despite marginal thermals at onset (especially across the
Mid-Atlantic) precipitation will become increasingly all-snow, and
may be heavy at times as banded snow develops and pivots northeast.=20

This event should last no more than 12 hours in any given location,
and the exact placement, timing, and intensity of the jet streak
will create the important differences in snowfall placement and
amounts. While guidance continues to feature some differences,
there has been a reduction in spread this aftn which is reflected
by increasing probabilities for accumulating snowfall, especially
along the I-95 corridor from Washington, D.C. to NYC. At this time,
WPC probabilities suggest a 30-70% chance of at least 2 inches from
Washington to NY and onto Cape Cod, with the greatest potential for
4+ inches occurring from near Philadelphia through central Long
Island. While this will occur early Sunday morning, at least=20
briefly heavy snowfall rates will make for hazardous travel.


...Great Lakes...=20
Days 1-3...

Persistent troughing across the east will maintain cold=20
conditions, with multiple shortwaves and accompanying cold front
driving renewed CAA for lake effect snow (LES) with modest synoptic
snow also accompanying each impulse. These impulses are most likely
to cross the region on Saturday, with another impulse on Monday.
While the accompanying synoptic/WAA snow is likely to produce only
modest accumulations, the post-frontal CAA will cause 850mb temps=20
to drop to as low as -20C to -25C Sat/Sun, with more tempered cold=20
of around -10C Monday. While the heaviest LES is expected
Saturday/Sunday as inversion depths over the lakes climb towards
10,000 ft, significant LES is also likely Monday despite the weaker
overall ascent/lake-induced instability.

WPC probabilities D1 and D2 are elevated, and feature a moderate
risk (30-70% chance) of exceeding 6 inches both days across the
southern shore of Lake Superior in the U.P. of MI, as well as
portions of NW L.P. near Traverse City, and across the Tug Hill
Plateau east of Lake Ontario. Slightly lower probabilities exist
along the Chautauqua Ridge. Snow totals of 1-2 feet are possible in
these areas as well. Then during D3 the flow becomes more westerly
focusing the heaviest LES across the Chautauqua Ridge and Tug Hill
Plateau where WPC probabilities indicate a high chance (>70%) for
additional snowfall of 6+ inches.

Weiss


...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-R0uB7_t2x6rqwmMIRkN23YJYqdVbS_8eeqYB5LOVq_UD= 5EiK3VDt10MQf31TpTfsOgP5R_0a9gVXeYjJXS3kl7W9zQ$=20


$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 130906
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
406 AM EST Sat Dec 13 2025

Valid 12Z Sat Dec 13 2025 - 12Z Tue Dec 16 2025


...North-Central Plains, Midwest to the Central Appalachians...=20
Day 1...

Low to mid-level low is over north shore of Lake Superior with a
reinforcing shortwave trough over far northeast MT. This wave is
riding a powerful 140kt jet that extends across the Midwest and
through the Mid- Atlantic. Intensifying fgen (both through WAA and
the result of the upper jet streak position) will be sufficient to
drive omega through the snow growth zone through this evening.=20
With strong lift occurring into a DGZ that is deepening in the cold
airmass, periods of heavy snow are expected, especially within a=20
narrow translating band from Iowa through Ohio and northern WV
today. Forcing is strong enough to warrant a risk for thundersnow=20 particularly midday/early afternoon over central IL/IN where 1"/hr
rates are possible per the 00Z HREF.=20
The bands rise over the Allegheny Plateau this evening where
orography once again brings a risk for 1"/hr rates. Day 1 PWPF for

6" are around 10% in central IL/IN and quickly increase from 40%

to 70% across far southeast OH through north-central WV. Snow rates
drop off Sunday morning over the central Appalachians, but the
upper trough does cross midday, so continued upslope snow showers
can be expected at least through the day light hours.


...Mid-Atlantic through Southern New England...=20
Days 1/2...

Upper low stalls over northern Lake Superior today before ejecting
southeast tonight with the aid of a reinforcing shortwave. The
resultant upper trough axis reaches the Northeastern Seaboard
Sunday evening with downstream surface trough then low development
off the Mid-Atlantic coast Sunday morning. Right entrance dynamics
aid fgen banding to develop in the lee of the central Apps later
this evening, most likely over north-central MD east through NJ
before the surface trough/low offshore provides additional forcing
for more intense banding overnight to shift south and east. This=20
system is fairly progressive, but the frontal forcing in
increasingly cold air allows 0.75"/hr rates in the Mid-Atlantic,
extending to southern New England early Sunday. Marginal thermals=20
at the southern extend of the precip swath to begin with quickly=20
shift to all snow - this is aided the nighttime occurrence.=20

This event should last no more than 12 hours in any given location,
and the exact placement, timing, and intensity of the jet streak
and offshore trough will determine where the heavier bands setup
and pivot. Day 1.5 PWPF for >6" are over 10% from just north of DC
through Cape Co with a peak of around 30% for greater Philly.=20


...Great Lakes...=20
Days 1-3...

Aforementioned low pressure system stalling over Lake Superior
today ejects southeast tonight with a reinforcing shortwave trough
passage on Monday. Subterranean DGZ under the low today makes for
coarse/low SLR snow, but some warming this evening brings back the
dendrites and 20:1 SLRs to the U.P.

Day 1 PWPF for >6" are 40-80% over NWly flow snow belts in the=20
eastern U.P. and east of Grand Traverse Bay. Wly flow snow belts
east of Lakes Erie/Ontario result in Day 1 PWPF >6" of 30-50% east
of Cleveland to the Chautauqua Ridge and over 80% for the Tug Hill
where single banding LES sets up this evening. Lull expected
for Sunday night as low level ridging shifts east of the Lakes. But
then shortwave crosses Monday with a decent, but transient swath of
lake enhanced snow. Light to locally moderate synoptically driven
snow across the Great Lakes region Monday with more single banding
in westerly flow over Lake Ontario into the Tug Hill where Day 3
PWPF for >6" is over 80%.=20


...Pacific Northwest...
Days 2/3...

Potent atmospheric river arrives Monday morning to western WA/OR
with snow levels skyrocketing up to 9000ft over the Cascades. A
shortwave trough passage over WA late Monday brings snow levels on
the North Cascades down to 5000ft, reaching 4000ft on Tuesday.
Lower precip rates are expected behind the trough passage, but
moderate snow brings Day 3 PWPF for >6" in the 40-60% range in the
high northern WA Cascades.=20


The probability of significant icing is less than 10 percent.=20

Jackson



...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_jPxnzcgK9JB0jlxCEYkNgPmBqDB9AV_xArz815tBmqPn= UJySnOPdk6IfueYnBtMZQh3ZGrHh9pNlUcp8ywHHzAOYSE$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 132003
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 PM EST Sat Dec 13 2025

Valid 00Z Sun Dec 14 2025 - 00Z Wed Dec 17 2025


...Upper Ohio Valley to Central Appalachians...
Days 1-2...

Moderate to heavy snow will be ongoing at the start of the forecast
period (00z Sun) across the Ohio Valley into the central
Appalachians with upslope snow continuing along the higher terrain
through Monday morning. A mid- level low associated with this=20
snowfall is over northeast shore of Lake Superior with a=20
reinforcing shortwave trough over the Upper Midwest. This wave is=20
riding a powerful 140kt jet that extends across the Midwest and=20
through the Mid- Atlantic. Intensifying 700 mb fgen (both through=20
WAA and the result of the upper jet streak position) will be=20
sufficient to drive omega through a wide (greater than 100 mb) snow
growth zone through this evening. With strong lift occurring into=20
a DGZ that is deepening in the cold airmass, periods of heavy snow=20
and high snow ratios (around 20:1) are expected, especially within=20
a narrow translating band from Ohio into northern WV today,=20
southwest PA and far western MD tonight.
=20
The bands rise over the Allegheny Plateau this evening where
orography brings a risk for 1"/hr rates. Following this system a=20
strong arctic cold front pushes southward and promotes lake=20
enhanced upslope flow into the high elevations of southwest PA,=20
western MD, and WV. Day 1 PWPF for >6" are around 40% to 70% across
north- central WV into western MD and southwest PA.


...Mid-Atlantic through Southern New England...=20
Day 1...

The same system impacting the Ohio Valley shifts towards the Mid-
Atlantic and Northeast tonight as the upper low stalls over=20
northern Lake Superior before ejecting southeast with the aid of a
reinforcing shortwave. The resultant upper trough axis reaches the
Northeastern Seaboard Sunday evening with downstream surface=20
trough then low development off the Mid- Atlantic coast Sunday=20
morning. Strong right entrance dynamics aid fgen banding to=20
develop in the lee of the central Apps later this evening, most=20
likely over north-central MD east through NJ before the surface=20
trough/low offshore provides additional forcing for more intense=20
banding overnight and shifts the band south and east. This system=20
is fairly progressive, but the frontal forcing in increasingly cold
air allows 0.5-1.0"/hr rates in the Mid- Atlantic, extending to far=20
southern New England early Sunday. Marginal thermals at the=20
southern extend of the precip swath to begin with quickly shift to=20
all snow - this is aided by the nighttime occurrence. Snow ratios=20
could tip the scales to higher end amounts across parts of eastern=20
PA through Long Island and southern New England as omega intersects
with a wide DGZ as the precipitation shield pulls eastward,=20
supporting ratios closer to 15-20:1 and much higher than=20
climatology.

This event should last no more than 6-12 hours in any given=20
location, and the exact placement, timing, and intensity of the jet
streak and offshore trough is still somewhat uncertain. Today's=20
guidance trended a tick north and wetter due to a more amplified=20
upper trough and related right entrance region of a 150kt upper=20
jet. Day 1 PWPF for >6" are 30-50% from north-central MD through=20
southeast PA and central NJ. Probabilities for >6" are 20-40%=20
across Long Island and Cape Cod, including the islands off southern
New England. Given most of this snow is expected to occur=20
overnight and during a weekend, impacts may be limited, but strong=20
cold air advection following the event and very cold temperatures=20
could pose a danger for individuals caught unprepared outdoors. Be=20
sure to check conditions before traveling in this region tonight or
tomorrow morning.


...Great Lakes...=20
Days 1-3...

Aforementioned low pressure system stalling over Lake Superior
today ejects southeast tonight with a reinforcing shortwave trough
passage on Monday. Subterranean DGZ under the low today makes for=20
coarse/low SLR snow, but some warming this evening brings back the=20
dendrites and 20:1 SLRs to the U.P.

Day 1 PWPF for >6" are 40-80% over NWly flow snow belts in the=20
eastern U.P. and east of Grand Traverse Bay. Wly flow snow belts
east of Lakes Erie/Ontario result in Day 1 PWPF >6" of 30-50% east
of Cleveland to the Chautauqua Ridge and over 80% for the Tug Hill
where single banding LES sets up this evening. Lull expected
for Sunday night as low level ridging shifts east of the Lakes. But
then shortwave crosses Monday with a decent, but transient swath of
lake enhanced snow. Light to locally moderate synoptically driven
snow across the Great Lakes region Monday with more single banding
in westerly flow over Lake Ontario into the Tug Hill where Day 2.5
PWPF for >8" is over 80%.=20


...Pacific Northwest...
Days 2-3...

Potent atmospheric river arrives Monday morning to western WA/OR
with snow levels skyrocketing up to 9000ft over the Cascades. A
shortwave trough passage over WA late Monday brings snow levels on
the North Cascades down to 5000ft, reaching 4000ft on Tuesday.
Lower precip rates are expected behind the trough passage, but
moderate snow brings Days 2-3 PWPF for >8" in the 60-90% range in=20
the high northern WA Cascades. Additional snow is expected for=20
this region after the short range forecast period ends by 00z=20
Wednesday.


The probability of significant icing is less than 10 percent.=20

Snell/Jackson




...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-y-EFOck4oiKPgryVMGcuJlO-9X4V4gIhgBlgpoo6TrGq= 8zrlWJ3ICxvhtyTseLzEz-LhdzxdCQUXLelwpLyVjJSkVU$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 140851
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
351 AM EST Sun Dec 14 2025

Valid 12Z Sun Dec 14 2025 - 12Z Wed Dec 17 2025


...Mid-Atlantic through Southern New England...=20
Day 1...

Positive tilt to the trough rounding the mid-level low centered=20
over Lake Huron this morning will continue to dig southeast as it=20
shifts across the Northeast through this evening. Surface low=20
development is underway along the Delmarva coast with rapid=20
strengthening today as it shifts northeast out to sea. Decent fgen
driven snow banding with rates around 1"/hr will continue to shift
south over the Mid-Atlantic as they begin to wrap around the sfc=20
low. These bands have reached the southeast Mass Cape and Islands=20
where they will pivot through the day and become ocean/bay enhanced
this evening as the low begins to pull away. This should result in
around 0.75" QPF which will be all snow with totals tempered a bit
from still warm waters. Day 1 PWPF for >4" after 12Z is generally=20
limited to Cape Cod and the Islands with probabilities of 40-70%.=20

Day 1 PWPF for an additional 2" after 12Z are generally 40-70% from
Rhode Island across Long Island, down the Jersey shore through
lower Delaware with 30% probs into the Northern Neck of VA and the
southern Delmarva.=20

Upslope snow rates west of the Allegheny Front dwindle through=20
sunrise with Day 1 PWPF for an additional 2" after 12Z are generally
30-70% for elevations in central WV above 2500ft.=20


...Great Lakes...=20
Days 1-2...

Aforementioned low pressure system ejecting southeast from Lake
Huron today will activate Nly flow snow belts into the east-central
U.P. where Day 1 PWPF for >4" are 40-70%.

WNWly flow over the eastern Great Lakes this morning will veer
NNWly by this evening with pivoting bands from Erie and Ontario.
Day 1 PWPF for >4" are 30% inland from Erie, PA and 50-80% just
north of Syracuse.=20

Lull in LES expected tonight as low level ridging shifts east over=20
the Lakes. But a shortwave clipper approaches from the northwest
late tonight and crosses Monday with a decent, but transient swath
of lake enhanced snow over the northern Lakes before prompting
singl-band LES over the Eastern Great Lakes Monday night with the
DGZ centered on 850mb. Day 2 PWPF for >2" is 40-70% from the
Keweenaw Peninsula through the eastern U.P. and Tip of the Mitt
while there are 30% probs for >6" south of Buffalo and 60-80% for
the Tug Hill Plateau.=20

A return of ridging cuts off the eastern LES early Tuesday.


...Cascades and Northern Rockies...=20
Days 2-3...

Potent atmospheric river arrives early Monday morning to western=20
WA/OR with snow levels skyrocketing up to 9000ft over the Cascades.
A shortwave trough passage over WA late Monday quickly brings snow
levels on the North Cascades back down to 5000ft by the evening,=20
reaching 4000ft overnight. Lower precip rates are expected behind=20
the trough passage, with Day 2 PWPF for >6" limited to the higher
WA Cascades. However, snow levels rise only a little Tuesday ahead
of the next wave that arrives Wednesday night. Precip rates
increase as snow levels remains around 4500 to 6000ft on the WA/OR
Cascades. Day 3 PWPF for >8" is over 80% across the higher WA
Cascades. Moisture surges inland TUesday night with snow levels of
5000 to 6000ft over the ID/MT ranges where Day 3 PWPF for >6" are
40-80%.=20


The probability of significant icing is less than 10 percent.=20

Jackson



...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!7rvAaj0lLWZVY_TM7YoX9IeN2Ah4F8vzFTtQgGyXcwy4Y= xpcVr37fwinGgFe9tgIQhTfLNcNrbGExXJTyqGUJs5FyY8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 141840
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
140 PM EST Sun Dec 14 2025

Valid 00Z Mon Dec 15 2025 - 00Z Thu Dec 18 2025


...Great Lakes...=20
Days 1-2...

Shortwave over western Ontario will dive southeastward tonight,=20
bringing a chance of light snow to the upper Lakes. The system will
bring a relatively brief period of lake enhanced snow to the lower
Lakes Monday followed by some lake effect snows off Ontario into=20
the Tug Hill before waning on Tuesday as heights rise. WPC=20
probabilities for at least 4 inches of snow are highest over the=20
eastern U.P., northwestern PA into NY, and most especially into the
Tug Hill as any banding will be rather variable.=20


...Cascades and Northern Rockies...=20
Days 2-3...

A lead warm atmospheric river (AR) will bring mostly rain to the=20
PacNW Monday with high snow levels. Cooler post-frontal air mass=20
will allow for lowering snow levels Tuesday to around 4000-5000ft=20
amid lighter QPF. There, WPC probabilities for at least 8 inches of
snow are highest (>50%). The stronger/colder AR will push into the
region Wednesday though the highest PW/IVT anomalies will be south
of the region. Nevertheless, strong upslope flow will capitalize=20
on available moisture coincident with lowering snow levels to bring
modest accumulating snow to the passes. Snow levels by Wednesday=20
evening will drop to around 2000-2500ft (700mb temps down below
-12C) with still modest QPF over the region. Increasingly heavier
snow will push down the terrain and continue beyond this forecast
period (00Z Thursday). Through then, WPC probabilities for at
least 8 inches of snow are >50% above 2500ft or so (which includes
Snoqualmie Pass).=20

Moisture surge and breezy/windy conditions will progress eastward=20
into the Northern Rockies/Divide with WPC probabilities for at=20
least 8 inches of snow >50% above 5000ft (north) to around 8000ft=20
(south, over WY). WSSI-P is showing some probabilities of moderate=20
impacts from blowing snow over the higher elevations in MT into WY.



The probability of significant icing is less than 10 percent.=20

Fracasso


...Extreme Cold Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9_tjz_IwQPRthuZ6wUbaCmmWc8O0jOXZgjxMcflb1cRhe= kv_NaWx0Qh64XBCw6s3ZHL1cPXujRkgANFS9sLTzxEIHFw$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 150848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EST Mon Dec 15 2025

Valid 12Z Mon Dec 15 2025 - 12Z Thu Dec 18 2025


...Great Lakes...
Day 1...

Some lake enhanced snow for Michigan this morning ahead of a
shortwave trough currently over the Arrowhead of MN. The greater
impacts are on the eastern Great Lakes where flow is already
backing westerly. Brief single-banding LES occurs this afternoon
off Lake Erie into the South Towns of Buffalo where Day 1 PWPF for

4" are around 60%. The greater LES formation is this evening with single-banding into the Tug Hill Plateau through the night before

tapering off Tuesday morning in notable warm air advection. The
saturated layer gets into the DGZ and the flow is fairly steady
state, so decent snows are forecast. Day 1 PWPF for >8" are around
80% for the Tug Hill.


...Cascades and Northern Rockies...
Days 1-3...

A lead warm atmospheric river (AR) will bring mostly rain to the
PacNW through early afternoon with very high snow levels around
9000ft. A shortwave trough brings a cold front through by this
evening which will lower snow levels this evening amid lighter QPF
to around 4000ft in WA 5000ft in northern OR. Day 1 PWPF for >8"
are limited to the higher WA Cascades.

Snow levels rise back to 5000ft in WA and 6000ft in OR Tuesday as
the next moisture surge pushes inland. However, a sharper shortwave
trough axis pushes across the Cascades by 12Z Wednesday. This
potent cold front brings a sharp drop in snow levels after 06Z
Wednesday to around 2000ft in WA and 4000ft in OR. Again, the
precip rates rapidly drop with the snow levels, but there should be
impactful snow at pass levels including Snoqualmie. Day 2.5 PWPF
for >8" are over 80% for most of the WA Cascades. Low snow levels
and precip rates persist then through Wednesday night.

Moisture and windy conditions will progress eastward over the
Northern Rockies this afternoon and much more so Tuesday night.
Day 1.5 snow probs for >8" are 30-60% over the northwestern MT
ranges. Day 2.5 snow probs for >8" are 50-80% over the western MT,
central ID, and northwest WY ranges with rapid drops in snow
levels.


The probability of significant icing is less than 10 percent.

Jackson


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 152028
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 PM EST Mon Dec 15 2025

Valid 00Z Tue Dec 16 2025 - 00Z Fri Dec 19 2025


...Great Lakes...
Day 1...

Warm advection around the northern periphery of a bubble of high
pressure centered over the Southeast U.S. will result in the
development of a single lake effect snow band off Lake Ontario this
evening, focused into the Tug Hill Plateau through the night
before tapering off Tuesday morning. Model soundings depict strong
and saturated lift within a deep DGZ, supporting moderate to heavy
snow across the Tug Hill. As a result, WPC probabilities are
moderate (40-60%) for snow accumulations >8", and high (>70%) for
accumulations >6".


...Cascades and Northern Rockies...
Days 1-3...

After a shortwave trough brings a cold front through this evening,
which will lower snow levels amid lighter QPF to around 4000ft in
WA and 5000ft in northern OR, snow levels are progged to rise back
to 5000ft in WA and 6000ft in OR Tuesday as the next moisture surge
pushes inland. However, a sharper shortwave trough axis pushes
across the Cascades by 12Z Wednesday. This potent cold front brings
a sharp drop in snow levels after 06Z Wednesday to around 2000ft
in WA and 4000ft in OR. Again, the precip rates rapidly drop with
the snow levels, but there should be impactful snow at pass levels
including Snoqualmie. Low snow levels and precip rates persist then
through Wednesday night before another push of moisture and
mountain snow move in during the day on Thursday. The latest WPC
probabilities remains high for snowfall accumulations >8"
(particularly for the Washington Cascades) each day from days 1-3,
with 72-hour probabilities through Thursday remaining high for
accumulations >24".

Moisture and windy conditions will progress eastward over the
Northern Rockies Tuesday night into Wednesday, followed by another
surge on Thursday, with falling snow levels. The latest WPC
probabilities for snowfall >8" are moderate to high (40-80%) for
the highest elevations of northern ID and western MT Day 1,
increasing to high (>70%) for a larger footprint of ranges across
ID, western MT, and western WY Day 2. Probabilities of >8" then
drop back to 30-70% for Day 3, with most confined to ID and WY.


...Northern Plains and Upper Midwest...
Day 3...

A strong area of low pressure (minimum MSLP currently modeled
outside of climatology) progged to track eastward along the
U.S./Canada border roughly from Montana to the Upper Great Lakes
will support a swath of moderate to heavy snowfall within the
deformation zone / cold comma head across portions of the northern
Plains and Upper Midwest later Wednesday night into Thursday.
Relatively fast forward speed should put a cap on the overall
potential from an accumulation standpoint, but even so, the latest
WPC probabilities for snowfall >4" are moderate to high (40-70%)
across northeast ND and northern Minnesota, with odds of 10-30% for

8". Regardless of snow accumulations, impacts could be more

notable than typical as a result of a very tight pressure gradient
and the potential for blowing and drifting snow due to strong gusty
winds.


The probability of significant icing is less than 10 percent.

Miller/Jackson


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 160835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Tue Dec 16 2025

Valid 12Z Tue Dec 16 2025 - 12Z Fri Dec 19 2025


...Cascades and Northern Rockies...
Days 1-3...

Snow levels on the WA Cascades rise from 4000ft to 5500ft through
this evening under brief ridging until a sharp shortwave trough
axis pushes across the Cascades by 12Z Wednesday on the head of a
170ft WNWly jet. This potent cold front brings a sharp drop in
snow levels tonight, reaching 2000ft in WA and 4000ft in OR early
Wednesday. The precip rates rapidly drop with the snow levels, but
there should be impactful snow at pass levels including
Snoqualmie. Low snow levels and moderate precip rates persist into
Thursday before an intense push of moisture and height rises move
in, particularly into Oregon. The latest WPC probabilities remain
high for snowfall accumulations >8" (particularly for the
Washington Cascades) each of days 1-3, with 72-hour probabilities
through Thursday remaining high for accumulations >24".

Moisture and windy conditions will progress eastward over the
Northern Rockies today, followed more surges tonight and Thursday,
with falling snow levels. The latest WPC probabilities for
snowfall >8" are moderate to high (40-80%) for the highest
elevations of central and northern ID and western MT Day 1,
expanding south through western Wyoming with 40-80% probs on Day
2, and then an increase over similar areas of MD/ID/WY on Day 3
with to 50-90%.


...Northern Plains, Upper Midwest, Great Lakes...
Day 3...

Strong low pressure tracks eastward along the U.S./Canada border
roughly from Montana to Lake Superior Wednesday through Thursday. A
wintry mix is possible in the warm air advection ahead of the
system over the Upper Midwest Wednesday night, but the main concern
is the leading axis of heavy snow on the cold conveyor belt that
connects to a wrap around deformation band with an intense pressure
gradient and high wind/blizzard threat. Fairly fast forward motion
and the likelihood that most of the leading bands should be north
of the border limits the overall snowfall for the U.S. That said,
Day 2.5 WPC probabilities for snowfall >4" remain moderate
(40-70%) from northeast ND through far northern Minnesota, with
10-30% for >8" in the northern Arrowhead. In general, the wind
field should be worst south of the new snow, but over the Dakotas
and Minnesota which has a decent snowpack that could be driven into
ground blizzard conditions. Please stay tuned on this wind-whipped
forecast.


The probability of significant icing is less than 10 percent.

Jackson



$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 162056
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 PM EST Tue Dec 16 2025

Valid 00Z Wed Dec 17 2025 - 00Z Sat Dec 20 2025


...Cascades and Northern Rockies...=20
Days 1-3...

An active period of winter weather persists across the Pacific
Northwest and Northern Rockies as pinched onshore flow pushes
considerable moisture onshore as an atmospheric river (AR). There
are some notable timing differences amongst the various global
ensembles as to when the most impressive IVT will move onshore, but
in general a core of elevated IVT (>80% chance to exceed 750
kg/m/s) will lift into WA/OR D2 ahead of a secondary front.

Before this occurs, a cold front will be moving across the Pacific
Northwest within another axis of elevated IVT D1, spreading
moisture from the coastal regions, across the Cascades, and as far
east as the Northern Rockies before 00Z Thursday. Impressive ascent
within the strong Pacific jet will combine with intensifying 700mb
fgen and periods of upslope flow to produce heavy precipitation
across the terrain. Snow levels during this time will rise ahead of
the cold front from around 4000 ft to 6000 ft, but then drop
rapidly in its wake to as low as 2000 ft. The heaviest snow is
likely ahead of the cold front so the most impactful snow will be
above pass levels, but impactful snow is likely at the Cascade
passes behind the cold front. WPC probabilities D1 for 6+ inches
are expansive across the Olympics, Cascades, Northern Rockies from
Glacier NP through the Salmon River/Sawtooth range, and around
Yellowstone NP, reaching above 70% across most of these areas with
snow levels varying from above 5000 ft east, to just 2000-3000 ft
west.

Moisture briefly decreases early D1 behind the first wave, but then
increasing rapidly again as the second and more impressive IVT
surge lift E/NE into the area. This will again be accompanied by a
frontal wave so snow levels will rise rapidly, reaching 6000-8000
ft within the strongest WAA/AR across OR/southern ID/southern
MT/WY, while remaining low at 2000-4000 ft farther north. While
snow levels will be lower north, the heaviest precipitation is
expected south/along the approaching front, with a heavy and wet
snow impacting much of the area before snow levels rise. This=20
could be impactful despite the rising snow levels due to the snow=20
load potential of a sub-climo SLR snow event within the AR, so=20
although the heaviest snow accumulations are likely above 7000 ft,=20
notable impacts are likely well below that elevation. WPC=20
probabilities D2 are high (>70%) for 6+ inches of snow in the=20
Cascades, Olympics, and Blues, expanding into much of the NW=20
terrain from the Cascades through the area around Yellowstone NP in
NW Wyoming D3. 3-day total snowfall of 3-4 feet is likely in the=20
higher terrain of much of the NW, with locally more than 6 feet in=20
the highest Cascades likely.


...Northern Plains, Upper Midwest, Great Lakes...=20
Days 2-3...

A strong low pressure moving along or near the Borderlands of
ND/MN/Canada will bring impactful winter weather (as well as a
variety of other hazards) to the region through late week.

A potent shortwave emerging from the Pacific Northwest/British
Columbia Wednesday afternoon will be the driver of this developing
system as it tracks rapidly eastward embedded within pinched zonal
flow. This shortwave will amplify as it dives into the Northern
High Plains, closing off to manifest as 700-500mb height anomalies
falling below the 1st percentile according to NAEFS. As this low
tracks east it will interact with a powerful 160kt Pacific jet
streak diving across the Northern Rockies to create an intense
surface low pressure. While there continues to be some intensity
and latitudinal spread among the ensemble systems of this surface
low (ECENS north and strong, GEFS/CMCE farther south and a bit
weaker) the general trend is for a strong low moving along the
Canadian border from Wednesday aftn through Friday morning.=20

Downstream of this surface low, impressive theta-e advection will
surge northward from the Gulf, with a modest TROWAL potentially
developing as moisture curls back to the NW of the system and lifts isentropically. Beneath this modest TROWAL, which will be well
positioned into the LFQ of the strong jet streak, a band of heavy
snow is possible from north-central MT through far northern MN. The
progressive nature of this system will limit the potential for
heavy snow, but intense ascent into a deep DGZ will result in at
least a short period of heavy snow within a possible fgen-forced
band. This will result in an axis of at least 2" of snow, but the
greatest potential for 4+ inches will be from far northern ND into
the Arrowhead of MN D2, and then across the U.P. of MI D3 where WPC probabilities exceeding 50%.

Although the total snowfall from this event will be modest.
Increasingly strong winds, which will likely eclipse 50 mph in
gusts, will create dangerous travel due to blowing-snow or even
near-blizzard impacts. Additionally, the NAM SnSq parameter is=20
elevated along a cold front crossing MT and the Dakotas, producing
additional dangerous travel where any snow squalls develop late
Wednesday and Thursday.


...Great Lakes...
Day 3...

Secondary low pressure developing across Wisconsin will rapidly
strengthen and lift progressively northeast through MI and into
Canada on Friday. The intensity of this low will result in an
impressive surge of WAA and precipitation downstream, but this will
all fall as rain in the warming column. In the wake of this low,
however, strong CAA leading to rapid column cooling will move
across the Great Lakes to produce periods of lake effect snow (LES)
especially across the eastern U.P., northwest L.P., and east of
Lakes Erie and Ontario. Inversion depths are forecast to be
generally modest (850mb) and plentiful moisture will be somewhat
transient. Still, efficient forcing into the DGZ will likely
produce at least short periods of heavy LES, reflected by WPC
probabilities that reach 30-50% for 4+ inches east of Erie/Ontario,
and 10-30% in the other favored N/NW snow belts.


The probability of significant icing is less than 10 percent.=20

Weiss


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5zfyW7z50atNGCSNMWCRW7K3CpVFbHrJXRdkMBRxn1_d7= VeGKD6e6yxZQFOZHxKnsIWNKrxXT1T8nfNkMGRS_-PpD1w$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 170923
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 AM EST Wed Dec 17 2025

Valid 12Z Wed Dec 17 2025 - 12Z Sat Dec 20 2025


...Cascades and Northern Rockies...=20
Days 1-3...

Active weather pattern for the Pacific Northwest and Northern=20
Rockies continues into next week. As of 09Z, a mid level low is
apparent in satellite imagery over the northern BC coast with a
trough axis extending south to the OR Coast. Pacific moisture had
surged inland ahead of this trough and is reaching the northern
Rockies now per regional NEXRAD returns. Snow levels on the
Cascades are quickly crashing to around 2000ft in WA and 3000ft in
OR with moderate precip rates persisting behind this cold front
today bringing impactful snow below pass level. The lower snow=20
levels spread across the northern Rockies through midday. Precip
rates briefly drop to light tonight. Day 1 WPC snow probs for >8"=20
are 60-90% for the WA Cascades as well as the higher western WY=20
ranges, and more like 40-80% for the northern OR Cascades, much of
western MT ranges through central ID and the Uinta in UT and=20
northern CO ranges.=20

A focused and powerful atmospheric river (AR) surges into the=20
northern OR coast Thursday before shifting south down the coast=20
through far northern CA Thursday night and Friday. Snow levels in=20
the core of this AR will rise to over 9000ft in OR and 5000 to
6000ft in WA through Thursday with a powerful cold front shifting
south over WA Thursday night. Moisture and higher snow levels push
over the northern Rockies ahead of this cold front Thursday night=20
with levels generally 5000 to 7000ft over MD/ID/WY with the cold
front pushing south over this area Friday/Friday night. Day 2 WPC=20
snow probs for >8" are 60-90% over the WA Cascades again and 50-80%
over the western MT/central ID ranges, and 40-80% over the western
WY ranges. Day 3 snow probs depict the southern shift with 40-80%
chances for >8" on the WA and OR Cascades along with the
Bitterroots with 60-90% for the Sawtooth and western WY
ranges. For three day totals: A few feet are likely over much of=20
the northern Rockies and several feet over the higher Cascades.


...Northern Plains, Upper Midwest, Great Lakes...=20
Days 1-3...

Powerful and deep low pressure develops in the lee of the southern
Canadian Rockies today before tracking over northern North Dakota
tonight and northern Minnesota Thursday morning then across Lake
Superior Thursday afternoon and Ontario/Quebec Thursday
night/Friday.=20

The potent shortwave emerging from the Pacific Northwest/British
Columbia this afternoon will be the driver of this developing=20
system as it tracks rapidly eastward embedded within pinched zonal=20
flow. This shortwave will amplify as it dives over the Northern=20
High Plains, closing off to manifest as 700-500mb height anomalies=20
falling below the 1st percentile according to NAEFS. As this low=20
tracks east it will interact with a powerful 160kt Pacific jet=20
streak diving across the Northern Rockies to create the intense=20
surface low pressure.=20

Downstream of this surface low, impressive theta-e advection from=20
the Gulf, with a modest TROWAL developing as moisture curls back=20
to the NW of the system and lifts isentropically. Beneath this=20
modest TROWAL, which will be well positioned into the left exit of
the strong jet streak, a band of heavy snow is possible as far west
as north-central MT, but likely for northeast ND through far=20
northern MN. The progressive nature of this system will limit the=20
potential for heavy snow, but intense ascent into a deep DGZ will=20
result in at least a short period of heavy snow within a possible=20 fgen-forced band. The greatest risk for >6" snow is in the Day 1.5
range along the northern MN border where probs are around 60% with
greater than 30% probs for >2" over central ND through north-=20
central MN and the western U.P. Although the total snowfall from=20
this event will be modest, increasingly strong winds, which will=20
likely eclipse 60 mph in gusts, will create dangerous travel due=20
to blowing snow and potential blizzard impacts.=20

Additionally, the leading edge of comma head could trigger snow
squalls from eastern MT through the Dakotas into MN tonight through
Thursday.


...Great Lakes and Interior Northeast...
Days 2/3...

The mid level low tracks across Michigan Thursday night with
reinforcing troughs swinging the trough axis around it to a
negative tilt as it lifts over the Northeast Friday. In the wake=20
of this low, strong CAA crosses the Great Lakes to produce periods
of lake effect snow (LES) especially across the eastern U.P.,=20
northwest L.P., and east of Lakes Erie and Ontario. Inversion=20
depths are forecast to be generally modest (850mb) and plentiful=20
moisture will be somewhat transient. Still, efficient forcing into=20
the DGZ will likely produce at least short periods of heavy LES,=20
reflected by Day 2.5 WPC probabilities for >4" that are 30-50%=20
east of Erie/Ontario. The wrap around flow and CAA cross the
Interior Northeast late Friday with Friday night snows bringing
30-60% Day 3 probs for >4" to the Adirondacks, Greens and Whites.=20


The probability of significant icing is less than 10 percent.=20


Jackson



...Winter Storm Key Messages are in effect and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-wkywK3UnTwBsBGOP5kzkOpPMSOCFlGrg9M87ZLgN5Vlt= 6rWNw8ghAX9HduWamnpI4EpMeeT4XumTYQ_H2Ci64kK_q0$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 172100
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
400 PM EST Wed Dec 17 2025

Valid 12Z Wed Dec 17 2025 - 12Z Sat Dec 20 2025


...Cascades and Northern Rockies...=20
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the driver in the
seemingly endless barrage of atmospheric rivers that is delivering
copious amounts of snow to the mountains of the Pacific Northwest
and the Northern Rockies. As a colder air-mass becomes entrenched=20
across the Columbia Basin and Northern Rockies. Snow levels are
between 2,500-3,000ft in the Cascades and as low as 2,000ft in the
Lewis Range at the onset as moderate precip rates persisting=20
behind this cold front today generate impactful snow below pass=20
level. Snow levels in the core of this AR will rise to over 9000ft=20
in OR Thursday morning and 5000 to 6000ft in WA by Thursday
afternoon with a powerful cold front shifting south over WA=20
Thursday night. Farther east, snow levels will rise to 6,000t in=20
the Bitterroots by Thursday night and approach 7,000ft in the
Sawtooth. Before the snow levels rise, however, strong 700mb FGEN
will support several hours of heavy snow at elevations as low as
6,000ft in central ID and 5,000ft in the Blue Mountains through=20
Thursday afternoon. Farther south, the Tetons, Absaroka, and Wind
River Ranges will reside closer to stronger 700mb jet and=20
anomalous PWATs, giving these ranges both an abundance of moisture=20
and strong upslope enhancement to keep heavy snow in the forecast=20
through Saturday morning for elevation at and above 7,000ft.=20

Prolonged Pacific moisture flux continues to be directed at OR and
into the Northern Rockies on Friday with higher snow levels that
support heavy snow in the more remote reaches of the Cascades and
Northern Rockies. The lone exception will be ongoing westerly upslope
flow into the WA Cascades where snow levels as low as 1,500ft are
expected. The bulk of the heaviest snowfall in the WA Cascades and
Olympics above 2,500ft. WPC 72-hour probabilities show high chances probabilities (>70%) for snowfall totals >24" at elevations between 3,000-4,000ft, while similar high chance probabilities exist above
4,000ft for snowfall totals >30". In the Rockies, high chance
probabilities (>70%) for >12" of snow are present above 5,000ft in
the Blue Mountains, Bitterroots, and the Lewis Range, while those=20
same probabilities for >24" are present above 6,000ft in the
Sawtooth. Snowfall in the Tetons and Wind River Ranges are likely
to range between 1-3 feet with some localized amounts approaching=20
4 feet in the more remote reaches of these ranges through=20
Saturday.

...Northern Plains, Upper Midwest, Great Lakes...=20
Days 1-3...

A potent shortwave trough, currently located over the Northern
Rockies, is forecast to amplify and close off in response to a 180
kt Eastern Pacific jet digging southward into the Four Corners=20
today. At the surface, a strong sub-980 mb low pressure center=20
will track southeastward into the Northern Plains, before an=20
emergent triple- point low migrates across the Upper Midwest=20
tomorrow and Friday.=20

As this low ejects eastward tonight, strengthening theta-e
advection from the Gulf combined with moist eastern Pacific inflow
will result in precipitable water anomalies in the 99th percentile
upstream of a developing TROWAL on the northwest flank of the low=20
center. With the entrance region of a strengthening jet streak=20
situated over the Canadian prairie, a heavy snow band is expected=20
to develop in the comma-head region roughly from a Glasgow to=20
Bemidji line. The progressive nature of this system will cap=20
overall heavy snow potential, but intense ascent superimposed with=20
a deep DGZ will yield at least a brief window for heavy snowfall=20
tonight and tomorrow morning. The latest WPC probabilities for >6"=20
of snow have dipped somewhat compared to the latest cycle, but=20
still highlight a 40-50% chance through Day 1 immediately along the International Border, while 70-90% probabilities for >2" of=20
snowfall are noted in adjacent areas. Although the total snowfall=20
from this event may look modest for this region, strong wind gusts=20
upwards of 70 mph will lead to dangerous travel due to blowing snow
and potential blizzard impacts. Along the same lines, snow squalls
remain possible along the leading edge of a surging Arctic front=20
across eastern Montana, the Dakotas, and Minnesota through=20
tomorrow.=20

The probability of significant icing is less than 10 percent.=20


Mullinax/Asherman/Jackson




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4RZVcz-ODCFsrekcV_tv1tRZsR5od7QH8Qcqffv7d5tsg= yOJC5zCU-vAU2n-70KlUZF_YjQ95dWWP79tX5RKZgUhHJ8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 180828
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Thu Dec 18 2025

Valid 12Z Thu Dec 18 2025 - 12Z Sun Dec 21 2025


...Blizzard conditions continue in the northern Plains today. See=20
Key Messages linked at the bottom of the discussion for more=20
information...

...Northern Plains, Upper Midwest, Great Lakes...=20
Days 1-2...

By the start of the forecast period (12z Thurs.) a very strong and
mature mid-latitude cyclone is expected to be located across
northern Minnesota, with an estimated central pressure in the low
980s mb. This would place it within record low territory for the
region in mid-late December. The depth of this low pressure system
alone will continue to exhibit a tight pressure gradient on the
northern and western flanks, creating very strong winds (gusts up=20
to 70 mph) where snowfall is also the primary precipitation type
and some lingering snowpack still exists.

Strong theta-e advection from the Gulf combined with moist eastern
Pacific inflow will result in precipitable water anomalies above=20
the 97.5th percentile upstream of a developing TROWAL on the=20
northwest flank of the low center. With the right entrance region=20
of a strengthening jet streak situated over the Canadian prairie, a
heavy snow band is expected along the MN-Canadian border today. Some
isolated snow squalls are also possible underneath the mid-level
circulation as it dives southeast from the Dakotas into southern
MN tonight. The latest WPC probabilities for >6" on Day 1 highlight=20
20-50% chances across northern MN. Although the total snowfall from
this event may look modest for this region, strong wind gusts=20
upwards of 70 mph will lead to dangerous travel due to blowing snow
and potential blizzard impacts, even outside of the area receiving
the most snowfall.

As this system continues eastward tonight into Friday, gusty winds
and developing lake effect snow are the most likely winter-related=20
hazards. 850 mb temperatures as low as -15C to -20C are expected
behind the strong cold front as lake temperatures remain largely
around 5C. This temperature delta and brief surge of west-
northwesterly flow will allow for heavy lake effect snow in the
typical snowbelts downwind of Lake Superior and Michigan, with
additional heavy snow possible downwind of Lake Erie and Lake
Ontario. The highest WPC probabilities for at least 6" of snow
through Saturday morning is across the Tug Hill Plateau downwind of
Lake Ontario, where chances sit at 40-70%.


...Cascades and Northern Rockies...=20
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the driver in the
seemingly endless barrage of atmospheric rivers that is delivering
copious amounts of snow to the mountains of the Pacific Northwest
and the Northern Rockies. The next surge of moisture is expected to
impact the Northwest during the day 1 period with a brief lull and
lowering snow levels on day 2 before the next round enters further
south across northern California on day 3. Meanwhile, moisture
continues to stream inland over the northern Rockies in order to
provide additional heavy mountain snowfall. Snow levels in the=20
core of this AR will rise to over 9000ft in Oregon this and 6000=20
to 7000ft in WA by this evening with a powerful cold front=20
shifting south over WA Thursday night crashing snow levels back
below 2000ft. Farther east, snow levels will rise to 6000t in the=20 Bitterroots by tonight and approach 7000ft in the Sawtooth. Before=20
the snow levels rise, however, strong 700mb FGEN will support=20
several hours of heavy snow at elevations as low as 6000ft in=20
central ID and 5000ft in the Blue Mountains through this evening.=20
Farther south, the Tetons, Absaroka, and Wind River Ranges will=20
reside closer to stronger 700mb jet and anomalous PWATs, giving=20
these ranges both an abundance of moisture and strong upslope=20
enhancement to keep heavy snow in the forecast through Saturday=20
morning for elevation at and above 7000ft.=20

Prolonged Pacific moisture flux continues to be directed at OR and
into the Northern Rockies on Friday with higher snow levels that
support heavy snow in the more remote reaches of the Cascades and
Northern Rockies. The lone exception will be ongoing westerly upslope
flow into the WA Cascades where snow levels as low as around 1500ft
are expected. The bulk of the heaviest snowfall in the WA Cascades
and Olympics is expected above 2500ft. WPC 72-hour probabilities=20
show high chances probabilities (>70%) for snowfall totals >24" at=20 elevations between 3000-4000ft, while similar high chance=20
probabilities exist above 4,000ft for snowfall totals >30". In the=20
Rockies, high chance probabilities (>70%) for >12" of snow on days
1 to 2 are present above 5,000ft in the Blue Mountains,=20
Bitterroots, and the Lewis Range, while those same probabilities=20
for >24" are present above 6,000ft in the Sawtooth. Snowfall in the
Tetons and Wind River Ranges are likely to range between 1-3 feet=20
with some localized amounts approaching 4 feet in the more remote=20
reaches of these ranges through Saturday. Strong winds are also
likely to be a concern across the Wyoming ranges, leading to
extreme impacts in the WSSI due to blowing snow.


The probability of significant icing is less than 10 percent.=20


Snell



...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-K8TNenTJXwRe3bckbpOSQRL-8xEEvGJg2vu5zjmjQ0HC= tcZRTvD9tBTol3sa3LMKyTE9MwiP-TKn9hM0S6v-TfWe20$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 182052
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
352 PM EST Thu Dec 18 2025

Valid 00Z Fri Dec 19 2025 - 00Z Mon Dec 22 2025


...Blizzard conditions continue in the Northern Plains through this
evening. See Key Messages linked at the bottom of the discussion=20
for more information...

...Northern Plains, Upper Midwest, Great Lakes...=20
Days 1-2...

At the beginning of the forecast period (00z Fri.) a strong 984 mb
cyclone is forecast to jog northeastward across Lake Superior into
Ontario. While snowfall is rapidly subsiding across the Northern=20
Plains, blizzard conditions will persist into early this evening=20
across portions of the eastern Dakotas and western Minnesota owing
to the gradient winds and fresh snowpack. 1-2" of blowing snow is
also expected over portions of the Minnesota Arrowhead and Upper=20
Peninsula of Michigan, which will support periods of hazardous=20
travel through early tomorrow.=20

As this system continues eastward tonight into Friday, gusty winds
and developing lake effect snow are the most likely winter-related=20
hazards. 850 mb temperatures as low as -15C to -20C are expected
behind the strong cold front as lake temperatures remain largely
around 5C. This temperature delta and brief surge of west-
northwesterly flow will allow for heavy lake effect snow in the
typical snowbelts downwind of Lake Superior and Michigan, with
additional heavy snow possible downwind of Lake Erie and Lake
Ontario. The highest WPC probabilities for at least 6" of snow
through Saturday morning is across the Tug Hill Plateau downwind of
Lake Ontario, where chances sit at 40-70%.=20

...Cascades, Northern Rockies, & Northern California...=20
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the culprit in the=20
endless barrage of atmospheric rivers generating copious amounts=20
of snow throughout the mountains of the Pacific Northwest and the=20
Northern Rockies. A persistent feed of Pacific moisture continues=20
to stream as far east as the northern Rockies today. Snow levels=20
in the core of this AR will rise to over 9000ft in Oregon and=20
6000-7000ft in eastern WA. By this evening, a potent cold front=20
advancing south over western WA tonight leads to snow levels
crashing below 2000ft. Farther east, snow levels will rise to=20
6000t in the Bitterroots by tonight and approach 7000ft in the=20
Sawtooth. Before the snow levels rise, however, strong 700mb FGEN=20
is supporting several hours of heavy snow at elevations as low as=20
6000ft in central ID and 5000ft in the Blue Mountains through this=20
evening. Farther south, the Tetons, Absaroka, and Wind River Ranges
will reside closer to stronger 700mb jet and anomalous PWATs (>99th
ECMWF climatological percentiles through Friday afternoon), giving
these ranges both an abundance of moisture and strong upslope=20
enhancement to keep heavy snow in the forecast through Saturday=20
morning for elevation at and above 7000ft.=20

Prolonged Pacific moisture flux will drift southward on Friday with precipitation spreading across northern CA and continue through
Sunday. Snow levels dip to as low as 5,000ft in the Siskiyou and
Shasta, but they only fall in the 8,000-9,000ft elevations on
Saturday before increasing above 9,000ft on Sunday. The lone=20
exception to the higher snow levels and SLRs will be ongoing=20
westerly upslope flow into the WA Cascades where snow levels as low
as around 1,500ft on Saturday and 2,500 ft on Sunday. The bulk of=20
the heaviest snowfall in the WA Cascades and Olympics is expected=20
above 2500ft. WPC 72-hour probabilities show high chances=20
probabilities (>70%) for snowfall totals >18" between 3,000-
4000ft, while similar high chance probabilities exist above 4,000ft
for snowfall totals >30". In the Rockies, high chance=20
probabilities (>70%) for >12" of snow through Friday are present=20
above 5,000ft in the Blue Mountains, Bitterroots, and the Lewis=20
Range, while those same probabilities for >18" are present above=20
6,000ft in the Sawtooth. Snowfall in the Tetons and Wind River=20
Ranges are likely to range between 1-3 feet with some localized=20
amounts approaching 4 feet in the more remote reaches of these=20
ranges through Sunday. The WSSI is keying in on Extreme Impact
potential (extremely dangerous travel, damages to infrastructure=20
in the Wind River, Teton, and Absaroka ranges through Friday night,
largely in the higher reaches of these ranges. Still, Major=20
Impacts (significant travel disruptions) at intermediate=20
elevations of these ranges are likely with heavy snow and whiteout
conditions contributing to the impacts in these ranges to close=20
out the week.=20


The probability of significant icing is less than 10 percent.=20


Mullinax/AA/Snell




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5l8mDKSbTrGBB2HZ5yAGCRsE22fZKp_zFc6mg68TKkrT-= yNKKjx6qWc5iTxkj-ZSZYprAhzHoh0jGvl5g8UgyrjDGZo$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 190739
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
239 AM EST Fri Dec 19 2025

Valid 12Z Fri Dec 19 2025 - 12Z Mon Dec 22 2025


...Great Lakes & Northern New England...
Days 1-2...

Negatively tilted upper trough and associated strong cold front is
expected to swing across the Great Lakes and East Coast today
producing a rapid drop in temperatures and gusty winds. This setup
will also provide the opportunity for heavy lake effect and upslope
snow. 850 mb temperatures as low as -15C to -20C are expected
behind the strong cold front as lake temperatures remain largely
around 5C. This temperature delta and brief surge of west-
northwesterly flow will allow for heavy lake effect snow in the
typical snowbelts downwind of Lake Superior and Michigan, with
additional heavier snow possible downwind of Lake Erie and Lake
Ontario given the greater westerly component to the low-level
winds. The highest WPC probabilities for at least 6" of snow
through Saturday morning is across the Tug Hill Plateau downwind of
Lake Ontario, where chances sit at 70-90%. Additionally, some
light to moderate upslope post-frontal snowfall is possible along
the central Appalachians and northern New England elevated west-
northwest facing terrain. Here, WPC probabilities for at least 4
inches of snowfall through 18z Saturday range between 30-60%.


...Cascades, Northern Rockies, & Northern California...
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the culprit in the
endless barrage of atmospheric rivers and moist Pacific flow into
the western U.S. This will feed copious amounts of snow throughout
the mountains of the Pacific Northwest and stream as far east as the
Northern Rockies. The strongest IVT signal shifts southward over
the next few days and focuses over southern Oregon and especially
northern California this weekend. It is within this moisture plume
where the highest snow levels above 8000-9000ft reside, with much
lower snow levels to the north across the Pacific Northwest on Day
1 around 1000-2000ft. These lower snow levels also overspread the
northern Rockies by the end of Day 1 after starting in the
5000-6000ft range within the core of the ongoing Atmospheric River.
For the Tetons, Absaroka, and Wind River Ranges, this region will
reside closer to stronger 700mb jet and anomalous PWATs (>99th
ECMWF climatological percentiles through Friday afternoon), giving
these ranges both an abundance of moisture and strong upslope
enhancement to keep heavy snow in the forecast through Saturday
morning for elevation at and above 7000ft. For northern CA, snow
levels dip below 5,000ft in the Siskiyou and Shasta, but as
precipitation also wanes. These levels rise once again above
6000-7000ft with the next AR on Sunday.

The lone exception to the higher snow levels will be ongoing
westerly upslope flow into the WA Cascades as low pressure lingers
off the coast of British Columbia. Snow levels are also expected to
remain quite low and around 1,500ft on Saturday and 2,500 ft on
Sunday. The bulk of the heaviest snowfall in the WA Cascades and
Olympics is expected above 2500ft. WPC 72-hour probabilities show
high chances probabilities (>70%) for snowfall totals >18" between
3,000- 4000ft, while similar high chance probabilities exist above
4,000ft for snowfall totals >30". In the Rockies, high chance
probabilities (>70%) for >12" of snow on Day 1 are present above
5,000ft in the Blue Mountains, Bitterroots, and the Lewis Range,
while those same probabilities for >18" are present above 6,000ft
in the Sawtooth. Snowfall in the Tetons and Wind River Ranges are
likely to range between 1-3 feet with some localized amounts
approaching 4 feet in the more remote reaches of these ranges
including the next round on Sunday. The WSSI is keying in on
Extreme Impact potential (extremely dangerous travel, damages to
infrastructure in the Wind River, Teton, and Absaroka ranges
through Friday night, largely in the higher reaches of these
ranges. Still, Major Impacts (significant travel disruptions) at
intermediate elevations of these ranges are likely with heavy snow
and whiteout conditions contributing to the impacts in these ranges
to close out the week.


...Sierra Nevada...
Days 2-3...

Precipitation along the southern periphery of the AR plume begins
to sink southward towards the central Sierra Nevada by the end of
Day 1, but with snow levels near 9000ft. Multiple AR impulses
through early Monday are expected with snow levels potentially
dropping down to around 8000ft as these moisture plumes are aimed
at the northern/central Sierra Nevada. WPC probabilities for at
least 12 inches of snowfall on days 2-3 (ending 12z Monday) are
between 50-70% and primarily above 9000ft elevation. This is
possibly the start of a very active and impactful weather pattern
across California, with additional high elevation heavy snow likely
through the middle to end of next week.


The probability of significant icing is less than 10 percent.


Snell


$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 190744
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EST Fri Dec 19 2025

Valid 12Z Fri Dec 19 2025 - 12Z Mon Dec 22 2025


...Great Lakes & Northern New England...
Days 1-2...

Negatively tilted upper trough and associated strong cold front is
expected to swing across the Great Lakes and East Coast today
producing a rapid drop in temperatures and gusty winds. This setup
will also provide the opportunity for heavy lake effect and upslope
snow. 850 mb temperatures as low as -15C to -20C are expected
behind the strong cold front as lake temperatures remain largely
around 5C. This temperature delta and brief surge of west-
northwesterly flow will allow for heavy lake effect snow in the
typical snowbelts downwind of Lake Superior and Michigan, with
additional heavier snow possible downwind of Lake Erie and Lake
Ontario given the greater westerly component to the low-level
winds. The highest WPC probabilities for at least 6" of snow
through Saturday morning is across the Tug Hill Plateau downwind of
Lake Ontario, where chances sit at 70-90%. Additionally, some
light to moderate upslope post-frontal snowfall is possible along
the central Appalachians and northern New England elevated west-
northwest facing terrain. Here, WPC probabilities for at least 4
inches of snowfall through 18z Saturday range between 30-60%.


...Cascades, Northern Rockies, & Northern California...
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the culprit in the
endless barrage of atmospheric rivers and moist Pacific flow into
the western U.S. This will feed copious amounts of snow throughout
the mountains of the Pacific Northwest and stream as far east as
the northern Rockies. The strongest IVT signal shifts southward
over the next few days and focuses over southern Oregon and
especially northern California this weekend. It is within this
moisture plume where the highest snow levels above 8000-9000ft
reside, with much lower snow levels to the north across the Pacific
Northwest on Day 1 around 1000-2000ft. These lower snow levels
also overspread the northern Rockies by the end of Day 1 after
starting in the 5000-6000ft range within the core of the ongoing
Atmospheric River. For the Tetons, Absaroka, and Wind River Ranges,
this region will reside closer to stronger 700mb jet and anomalous
PWATs (>99th ECMWF climatological percentiles through Friday
afternoon), giving these ranges both an abundance of moisture and
strong upslope enhancement to keep heavy snow in the forecast
through Saturday morning for elevation at and above 7000ft. For
northern CA, snow levels dip below 5,000ft in the Siskiyou and
Shasta, but as precipitation also wanes. These levels rise once
again above 6000-7000ft with the next AR on Sunday.

The lone exception to the higher snow levels will be ongoing
westerly upslope flow into the WA Cascades as low pressure lingers
off the coast of British Columbia. Snow levels are also expected to
remain quite low and around 1,500ft on Saturday and 2,500 ft on
Sunday. The bulk of the heaviest snowfall in the WA Cascades and
Olympics is expected above 2500ft. WPC 72-hour probabilities show
high chances probabilities (>70%) for snowfall totals >18" between
3,000- 4000ft, while similar high chance probabilities exist above
4,000ft for snowfall totals >30". In the Rockies, high chance
probabilities (>70%) for >12" of snow on Day 1 are present above
5,000ft in the Blue Mountains, Bitterroots, and the Lewis Range,
while those same probabilities for >18" are present above 6,000ft
in the Sawtooth. Snowfall in the Tetons and Wind River Ranges are
likely to range between 1-3 feet with some localized amounts
approaching 4 feet in the more remote reaches of these ranges
including the next round on Sunday. The WSSI is keying in on
Extreme Impact potential (extremely dangerous travel, damages to
infrastructure in the Wind River, Teton, and Absaroka ranges
through Friday night, largely in the higher reaches of these
ranges. Still, Major Impacts (significant travel disruptions) at
intermediate elevations of these ranges are likely with heavy snow
and whiteout conditions contributing to the impacts in these ranges
to close out the week.


...Sierra Nevada...
Days 2-3...

Precipitation along the southern periphery of the AR plume begins
to sink southward towards the central Sierra Nevada by the end of
Day 1, but with snow levels near 9000ft. Multiple AR impulses
through early Monday are expected with snow levels potentially
dropping down to around 8000ft as these moisture plumes are aimed
at the northern/central Sierra Nevada. WPC probabilities for at
least 12 inches of snowfall on days 2-3 (ending 12z Monday) are
between 50-70% and primarily above 9000ft elevation. This is
possibly the start of a very active and impactful weather pattern
across California, with additional high elevation heavy snow likely
through the middle to end of next week.


The probability of significant icing is less than 10 percent.


Snell





$$

= = =
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 192022
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 PM EST Fri Dec 19 2025

Valid 00Z Sat Dec 20 2025 - 00Z Tue Dec 23 2025


...Great Lakes & Northern New England...=20
Days 1-2...

Negatively-tilted upper trough and associated strong cold front=20
will exit New England this evening with a sharp drop in=20
temperatures behind it. 850 mb temperatures as low as -15C to -20C=20
are expected behind the strong cold front as lake temperatures=20
remain largely around 5C. This temperature delta and brief surge of
west- northwesterly flow will support moderate to heavy lake=20
effect snow in the typical snowbelts downwind of Lake Superior and=20
Michigan, with additional heavier snow possible downwind of Lake=20
Erie and especially Lake Ontario given the greater westerly=20
component to the low-level winds. The highest WPC probabilities for
at least 8" of snow through Saturday are across the Tug Hill=20
Plateau downwind of Lake Ontario (70-90%). Additionally, some light
to moderate upslope post-frontal snowfall is possible across=20
northern New England over elevated west-northwest-facing terrain.=20
Here, WPC probabilities for at least 4 inches of snowfall through=20
Saturday range between 40-70%.


*** Atmospheric River to continue in the West into and through next
week ***

...Cascades, Northern Rockies, & Northern California...=20
Days 1-3...

An anchored -WPO/-PNA teleconnection pattern is the culprit in the
endless barrage of atmospheric rivers and moist Pacific flow into=20
the western U.S. This will feed copious amounts of snow throughout=20
the mountains of the Pacific Northwest and stream as far east as=20
the northern Rockies. The strongest IVT signal has shifted=20
southward today and will focus over northern California ENE across=20
the Great Basin to the WY ranges this weekend. It is within this=20
moisture plume where the highest snow levels above 8000-9000ft=20
reside, with much lower snow levels to the north in the colder air=20
mass across the Pacific Northwest (WA into OR) tonight around=20
1000-2000ft. These lower snow levels will continue to overspread=20
the northern and central Rockies tonight/Saturday after starting in
the 5000-7000ft range within the core of the ongoing Atmospheric=20
River. For the Tetons, Absaroka, and Wind River Ranges, this region
will reside closer to stronger 700mb jet and anomalous PWATs/IVT=20

98th climatological percentiles), giving these ranges both an=20

abundance of moisture and strong upslope enhancement to keep heavy=20
snow in the forecast through Saturday morning for elevation at and=20
above 7000ft. For northern CA, snow levels dip below 5,000ft in the
Siskiyou and Shasta, but as precipitation also wanes. These levels
rise once again above 6000-7000ft with the next AR on Sunday.

North of the AR, westerly upslope flow into the WA Cascades will=20
support much lower snow levels -- around 1,500ft on Saturday and=20
2,500 ft on Sunday. The bulk of the heaviest snowfall in the WA=20
Cascades and Olympics is expected above 2500ft, so this will=20
include nearly all the passes (e.g., Snoqualmie). WPC 72-hour=20
probabilities show high chances probabilities (>70%) for snowfall=20
totals >18" between 3000-4000ft, while similar high chance=20
probabilities exist above 4000ft for snowfall totals >30".

In the Rockies, snow will start to lessen tonight over the=20
Tetons/Wind River Range with additional light/modest accumulation=20
Day 1 of several inches, but perhaps more than a foot (>50%=20
probabilities) over the Uintas. For Days 2-3, additional snowfall=20
in the Tetons and Wind River Ranges are likely to range between 1-3
feet with some localized amounts approaching 4 feet in the more=20
remote reaches of these ranges as another surge of moisture=20
associated with the long-lived AR moves through. Major Impacts=20
(significant travel disruptions) are expected. Some light snow is=20
also expected in the CO Rockies tonight into Saturday.

...Sierra Nevada...
Days 1-3...

Precipitation along the southern periphery of the AR plume begins=20
to sink southward towards the central Sierra Nevada tonight, but=20
with snow levels near 9000ft. Multiple AR impulses through Monday=20
are expected with snow levels potentially dropping down to around=20
7500ft as these moisture plumes are aimed at the northern/central=20
Sierra Nevada. This may impact some of the passes across the crest=20
(e.g., Donner Pass at 7239ft) as snow levels dip/oscillate. The AR=20
event will continue beyond this forecast period into the medium=20
range. WPC probabilities for at least 12 inches of snowfall on days
1-3 (ending 00Z Tuesday) are between 50-70% and primarily above=20
9000ft elevation. Snow levels will trend a bit lower into Monday=20
and WPC probabilities for at least 4 inches of snow are >30% to=20
elevations around 7500ft. This is possibly the start of a very=20
active and impactful weather pattern across California, with=20
additional high elevation heavy snow likely through the middle to=20
end of next week. See our latest Key Messages that cover the event=20
through the end of next week, and CPC's Key Messages into week 2.


The probability of significant icing is less than 10 percent.=20


Fracasso/Snell


...Atmospheric River Key Messages are in effect. Please see=20
the link below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8sYtn0Wp774cnXpWXeT7AtfkTrDIam3_gR8MIUE4ki1Bk= zV6PsnZfiUuTi3j4YSONvYfbDAVkptvoOQj63yLjG5gmDs$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 200753
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EST Sat Dec 20 2025

Valid 12Z Sat Dec 20 2025 - 12Z Tue Dec 23 2025


...Great Lakes...
Days 1-2...
Maximum impact level from WSSI: Minor

Weather pattern across the Great Lakes quickly shifts away from=20
strong cold air advection as a shortwave crosses over the region=20
with an associated surface low tracking north of Lake Superior=20
towards southern Quebec by Sunday morning. This allows for some=20
moderate warm air advection snow across the Upper Great Lakes=20
followed by lake effect snow overnight behind a potent cold front.=20
This west-northwest flow returns to Lake Ontario and Lake Erie by=20
Sunday as well. All in all snowfall amounts from this system don't=20
appear that impressive given it's progressive nature. WPC=20
probabilities for at least 6 inches of snowfall are highest across=20
the eastern U.P. of MI and between 40-70%. Chances for at least 4=20
inches of snow downwind of Lake Ontario are low (20-40%) along its=20
southern shore and the Tug Hill through Day 2.


...Cascades, Northern Rockies, & Northern California...=20
Days 1-3...
Maximum impact level from WSSI: Major to Extreme

Deep upper troughing in eastern Pacific below the 10th
climatological percentile through at least early next week
continues to allow for an influx of westerly flow and Pacific
moisture into the western U.S. along with increasing IVT within a
wavering Atmospheric River. As moisture flux wanes across the
northern Rockies on Day 1 the next surge enters the region by the
start of Day 2 with snow levels starting around 5000ft across the
Sawtooths before steadily increasing throughout the region,=20
including the Absarokas, Tetons, and Wind River Range, up to=20
around 8000ft within the core of the moisture plume extending all=20
the way back to the central Pacific. Moisture will be plentiful as=20
PWs increasing to above the 99th climatological percentile over=20
northern UT and into WY. The heaviest snowfall is expected=20
throughout the ranges of central ID and western WY. WPC=20
probabilities for at least 18 inches of snowfall through Tuesday=20
morning are high (70-90%) across the Sawtooths of ID and Wind=20 River/Teton/Absaroka ranges of WY above 8000ft. Snowfall totals in=20
this region could top 2 to 3 feet.

Farther north and away from the immediate AR plume, persistent
westerly flow and lower snow levels are forecast to impact the
Pacific Northwest. Snow levels across the Cascades are expected to
start the forecast period around 2000ft and only briefly rise to
around 3000ft tonight before falling yet again to 2000ft on Monday.
This places all major passes at risk of heavy accumulating snowfall
and treacherous driving conditions. Snoqualmie (3022ft) and=20
Stevens Pass (4061ft) of particular note could see total snow=20
accumulations between 1 to 2 feet. WPC probabilities for at least 2
feet of snowfall are high (70-90%) across the WA Cascades above=20
4000ft, with high chances for at least 12 inches of snow above=20
3000ft. Moisture also continues to stream into the northern ID and=20
northwest MT ranges, where elevations above 5000ft have high=20
chances for at least 8 inches of snowfall over a 72-hr period.


*** Strong Atmospheric River to impact California and the Sierra
Nevada through next week ***

...Sierra Nevada...
Days 1-3...
Maximum impact level from WSSI: Major to Extreme

Multiple AR impulses through Tuesday are expected with snow levels
potentially dropping down to around 7500ft as these moisture=20
plumes are aimed at the northern/central Sierra Nevada, with the
strongest surge forecast on Sunday ahead of a strong shortwave.=20
This may impact some of the passes across the crest (e.g., Donner=20
Pass at 7239ft) as snow levels dip/oscillate. The AR event will=20
continue beyond this forecast period into the medium range. WPC=20 probabilities for at least 12 inches of snowfall on days 1-3=20
(ending 12Z Tuesday) are between 70-90% and primarily above 8500ft=20 elevation. Snow levels will trend a bit lower into Monday and=20
Tuesday as WPC probabilities for at least 4 inches of snow are >30%
to elevations around 7500ft. This is possibly the start of a very=20
active and impactful weather pattern across California, with=20
additional high elevation heavy snow likely through the middle to=20
end of next week. See our latest Key Messages that cover the event=20
through the end of next week, and CPC's Key Messages into week 2.


The probability of significant icing is less than 10 percent.=20


Snell



...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!68GdDrL0WuNUm2DNvJV3RZ1kO2Bp3LoaocoX2kDXlLn61= 3QYlpxY-MzlnpzPb72VtZyArvWymtpFbSYDITP7298IFM8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 202018
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
318 PM EST Sat Dec 20 2025

Valid 00Z Sun Dec 21 2025 - 00Z Wed Dec 24 2025


...Great Lakes...
Days 1-2... Maximum impact level from WSSI: Minor

Clipper system moving through southern Ontario will bring=20
generally light snow to the Great Lakes via warm air advection=20
first, followed by light to moderate lake effect snow over the U.P.
of Michigan and into the Tug Hill Plateau post-FROPA. Residence=20
time will be on the shorter side, limiting total accumulations=20
Sunday and early Monday. WPC probabilities for at least 6 inches of
snow are highest across the eastern U.P. of MI and between 40-70%.
Chances for at least 4 inches of snow downwind of Lake Ontario are
moderate (40-70%) along its southern shore and the Tug Hill=20
through Day 2.


...Northeast...
Day 3... Probability of at least Minor Impacts: >50%

Jet stream over the northern Plains to the Upper Midwest will help
carry a surface low pressure through southern Canada and a front=20
through the Great Lakes. Broad WAA ahead of the system over the=20
still cold Northeast will bring generally light snow to much of the
Northeast and northern Mid-Atlantic away from the immediate coast.
Some light freezing rain is possible on the southern edge of the=20 precipitation (central PA and perhaps into parts of WV) though the=20
highest QPF will lie over Northern/Upstate/Central NYS at the nose=20
of a 130kt jet through 00Z/Wed. WPC probabilities for at least 4=20
inches of snow are >50% in the Tug Hill (embedded probabilities=20

70%) as well as into the Green Mountains.

...Cascades, Northern Rockies, & Northern California...=20
Days 1-3... Maximum impact level from WSSI: Major to Extreme

Strong west-to-east 160+kt jet into Oregon will lift northward=20
tonight in response to digging heights along 140W. This will=20
maintain light to moderate precipitation over the Cascades and=20
downstream to the Northern Rockies on the cooler side of the=20
Atmospheric River that is positioned over Northern California. Snow
levels will remain on the lower side north of the moisture plume,=20
but continued upslope into the Cascades and Rockies will still=20
yield modest snow totals for these regions, especially days 1-2.=20
The incoming shortwave tomorrow night will briefly raise snow=20
levels in the WA Cascades from around 2000 to 3000ft, but then fall
again with some CAA behind the system. This will continue to=20
impact the passes in the region (e.g., Snoqualmie and Stevens)=20
where significant snow is likely. This may be focused around two=20
waves -- the initial one tonight/tomorrow with another Monday night
into Tuesday. WPC probabilities for at least 12 inches of snow for
the three-day period are >50% above 3000ft or so. Farther east,=20
snow levels around 4000-6000ft over the northern Rockies will rise=20
later tonight as heights rise and moisture increases. SW flow and=20
sufficient moisture will support lighter but still appreciable snow
compared to the Cascade over northern Idaho into northwestern=20
Montana, generally above 5000ft.=20

The strongest moisture flux will be in the core of the AR where PW
and IVT anomalies lie near/above the 99th percentile, generally in
an arc from the southern OR Cascades into the central/southern=20
Idaho ranges and into Wyoming. There, WSW to W flow will maximize=20 accumulations over parts of the Bitterroots and especially into the
Tetons, Absarokas, and Wind River Range. WPC probabilities for at=20
least 24 inches of snow over the three-day period are high (>70%)=20
over western Wyoming. High mountain peaks/ridges above=20
9000-10,000ft may see several feet of snow.=20


*** Strong Atmospheric River to impact California and the Sierra=20
Nevada through next week ***

...Sierra Nevada...
Days 1-3... Maximum impact level from WSSI: Major to Extreme

A long-lived Atmospheric River event will contain waves of=20
precipitation as embedded systems move inland from the Pacific over
the next several days (and beyond). An area of surface low=20
pressure will move inland across NorCal tonight/early Sunday and=20
bring heavier snow to the northern/central Sierra into early Monday
with snow levels around 8000-10,000ft from north to south. Snow=20
may impact some of the passes across the Sierra Crest though the=20
heaviest snow rates may be above 9000ft (2-3"/hr). Thereafter, the=20
moisture plume will lift northward and snow levels may lower a bit=20
into Tuesday with less accumulation overall except for the highest=20
peaks in the Shasta/Siskiyous and farthest north Sierra. This is=20
possibly the start of a very active and impactful weather pattern=20
across California, with additional high elevation heavy snow likely
through the middle to end of next week. See our latest Key=20
Messages that cover the event through the end of next week, and=20
CPC's Key Messages into week 2.


The probability of significant icing is less than 10 percent.=20

Fracasso


...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-8zQPUyCgrJcQnhUCXMvQ3b_nE5Ze81Ok5BTIcxjXD8Py= r7EUaeUp7XWbO2laLsh-nfWXFH7q8lMAJhKbriU0lGuQyc$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 210754
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Sun Dec 21 2025

Valid 12Z Sun Dec 21 2025 - 12Z Wed Dec 24 2025


...Upstate New York...
Day 1... Maximum impact level from WSSI: Minor

Clipper system racing across southeast Canada and a strong cold=20
front pushing across the Great Lakes and Northeast will provide the
chances for isolated snow squalls and a heavy lake effect snowband
downwind of Lake Ontario through tonight. Westerly flow around 40
kts at 850 mb and temperatures at this level around -15C will aid a
single snowband off Lake Ontario into Oswego and northern Oneida
counties. Flow bends towards a more northerly direction around 00Z
tonight before the band lifts back north on Monday. This wavering
will prevent significant snowfall accumulations, but moderate=20
amounts are still possible specifically prior to 00Z tonight. WPC=20 probabilities for at least 6 inches of snow are around 30-60% for=20
this region extending east from the southeast shores of Lake=20
Ontario.


...Northeast...
Days 2-3... Probability of at least Minor Impacts: >60%

Upper level pattern over CONUS by late day 2 includes an anomalous
ridge centered over the central U.S. and strong jet soaring to the
north along the U.S-Canadian border before aiming southeastward
across the Northeast, where slight troughing remains. An embedded
shortwave crossing north of the Great Lakes on Tuesday within a=20
divergent left-exit region of a strengthening 150kt jet streak will
aid in blossoming precipitation across the Northeast by Tuesday.=20
Broad WAA ahead of the system over the still cold Northeast will=20
bring generally light snow to much of the Northeast and northern=20
Mid- Atlantic away from the immediate coast as early as Tuesday
morning. Some light freezing rain is also possible on the southern
edge of the precipitation (central PA and perhaps into parts of=20
WV) though the highest QPF will lie over Northern/Upstate/Central=20
NYS to southern New England. Snow is expected to track across New=20
England on day 3 as the shortwave crosses over the region and could
help spin up a surface low in the Gulf of Maine. This may lead to=20
an inverted trough or quickly developing TROWAL maximizing QPF=20
potential across southern Maine, but high uncertainty remains=20
within the day 3 timeframe. WPC probabilities for at least 4 inches
of snow are currently 20-40% from NYS through much of New England=20
(excluding regions south of I-90).=20


...Cascades, Northern Rockies, & Northern California...=20
Days 1-3... Maximum impact level from WSSI: Major to Extreme

Digging heights near 135W in the eastern Pacific will help lift a
shortwave over the Northwest tonight as well as direct a resurgent
Atmospheric River into northern California with spillover=20
extending into the Northern Rockies. Snow levels will remain on the
lower side north of the moisture plume, but continued upslope into
the Cascades and Rockies will still yield modest snow totals for=20
these regions, especially days 1-2. The incoming shortwave tonight=20
will briefly raise snow levels in the WA Cascades from around 2000=20
to 3000ft, but then fall again with some CAA behind the system.=20
This will continue to impact the passes in the region (e.g.,=20
Snoqualmie and Stevens) where significant snow is likely. Heavy=20
snow in these regions of the Northwest and Northern Rockies may be=20
focused around two waves -- the initial one today/tonight with=20
another Monday night into early Tuesday. WPC probabilities for at=20
least 12 inches of snow for the three-day period are >50% above=20
3000ft or so.

Farther east, snow levels around 6000ft over the Northern Rockies=20
will rise today as heights rise and moisture increases. SW flow and
sufficient moisture will support lighter but still appreciable=20
snow compared to the Cascades over northern Idaho into=20
northwestern Montana, generally above 5000ft. The strongest=20
moisture flux will be in the core of the AR where PW and IVT=20
anomalies lie near/above the 99th percentile, generally in an arc=20
from the southern OR Cascades into the central/southern Idaho=20
ranges and into Wyoming. There, WSW to W flow will maximize=20
accumulations over parts of the Bitterroots and especially into the
Tetons, Absarokas, and Wind River Range. WPC probabilities for at=20
least 24 inches of snow over the three-day period are high (>70%)=20
over western Wyoming. High mountain peaks/ridges above=20
9000-10,000ft may see several feet of snow before precipitation
begins to wane on Tuesday.


*** Strong Atmospheric River to impact California and the Sierra
Nevada over the next several days ***

...Sierra Nevada...
Days 1-3... Maximum impact level from WSSI: Major to Extreme

A long-lived Atmospheric River event will contain waves of=20
precipitation as embedded systems move inland from the Pacific over
the next several days (and beyond). An area of surface low=20
pressure will move inland across NorCal today and bring heavier=20
snow to the northern/central Sierra into early Monday with snow=20
levels around 8000-10,000ft from north to south. Snow may impact=20
some of the passes across the Sierra Crest though the heaviest snow
rates may be above 9000ft (2-3"/hr). Thereafter, the moisture=20
plume will lift northward and snow levels may lower a bit into=20
Tuesday with less accumulation overall except for the highest peaks
in the Shasta/Siskiyous and farthest north Sierra. The next surge
of moisture is expected by the end of day 3 as the lingering AR
plume orients more north-south in response to height falls just off
the West Coast. Snow levels also fall with this next round to
around 6000-8000ft from north to south. WPC probabilities for at
least 12 inches of snowfall are 50-90% above around 8000ft through
12z Wednesday. This very active and impactful weather pattern=20
across California is expected to continue through at least the next
several days, with additional high elevation heavy snow likely into
the end of this week. See our latest Key Messages that cover the=20
event through the end of next week, and CPC's Key Messages into=20
week 2.


The probability of significant icing is less than 10 percent.=20

Snell/Fracasso



...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_FA_POhDFb5HJN-sUJ0i9jl8edjRRHh_SXBYQveL5RWit= qoz7Ca9u2HIoLQ1LcVdJwLI1W3MtAeUtLooha-m7g8eNWg$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 212011
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 PM EST Sun Dec 21 2025

Valid 00Z Mon Dec 22 2025 - 00Z Thu Dec 25 2025


...Upstate/Central New York...
Day 1... Maximum impact level from WSSI: Minor

Exiting trough will lead to an end to any lake effect snow over NY
east of ROC and near/south of Oswego to SYR. Additional snowfall=20
after 00Z tonight will be light, though some areas between Sodus=20
and Oswego could see another 4" of snow where WPC probabilities are

50%.=20

...Northeast...
Days 2-3... Probability of at least Minor Impacts: >70%

Upper level pattern over CONUS by Day 2 includes an anomalous=20
ridge centered over the central U.S. and strong jet soaring to the=20
north along the U.S-Canadian border before aiming southeastward=20
across the Northeast, where slight troughing remains. An embedded=20
shortwave crossing north of the Great Lakes on Tuesday within a=20
divergent left-exit region of a strengthening 150kt jet streak will
aid in blossoming precipitation across the Northeast by early=20
Tuesday. Broad WAA ahead of the system over the still cold=20
Northeast (especially just inland) will bring generally light snow=20
to much of the Northeast and northern Mid-Atlantic but some light=20
freezing rain on the southern edge of the precipitation shield=20
(central PA and perhaps into parts of WV). The highest QPF will lie
over Northern/Upstate/Central NYS into central New England within=20
the zone of strongest lower-level WAA as the surface warm front=20
lifts into the region. With the fast flow, the parent low over=20
Canada will get left behind as the front occludes and stretches=20
across New England, ultimately forming a new low in the Gulf of=20
Maine. This may lead to an inverted trough or quickly developing=20
TROWAL maximizing QPF/snow potential across southern Maine, but=20
uncertainty remains with the details. The system will pull away=20
from eastern New England late Wednesday afternoon and snow will=20
come to an end by the end of this forecast period. WPC=20
probabilities for at least 4 inches of snow are >50% over portions=20
of the Finger Lakes region northward to the Tug Hill and=20
Adirondacks, Green Mountains, and into the Maine Midcoast. The=20
highest probabilities for at least 6 inches of snow are over the=20
Tug Hill/Adirondacks.=20



...Cascades, Northern Rockies, & Northern California...=20
Days 1-3... Maximum impact level from WSSI: Major to Extreme

Digging heights near 135W in the eastern Pacific will help lift a=20
shortwave over the Northwest tonight as well as direct a resurgent=20 Atmospheric River into northern California with spillover extending
into the Northern Rockies. Snow levels will remain on the lower=20
side north of the moisture plume, but continued upslope into the=20
Cascades and northern Rockies will still yield modest snow totals=20
for these regions, especially days 1-2. The incoming shortwave=20
tonight will briefly raise snow levels in the WA Cascades from=20
around 2000 to 3000ft, but then fall again with some CAA behind the
system. This will continue to impact the passes in the region=20
(e.g., Snoqualmie and Stevens) where significant snow is likely.=20
Heavy snow in these regions of the Northwest and Northern Rockies=20
may be focused around two waves -- the initial one tonight with=20
another Monday night into early Tuesday. WPC probabilities for at=20
least 12 inches of snow for the three-day period are >50% above=20
3000ft or so.

Farther east, snow levels around 4000-8000ft over the Northern=20
Rockies (north to south) will rise a bit more tonight in advance of
more snow. SW flow and sufficient moisture will support lighter=20
but still appreciable accumulations compared to the Cascades over=20
northern Idaho into northwestern Montana, generally above 5000ft.=20
The strongest moisture flux will be in the core of the AR where PW=20
and IVT anomalies lie near/above the 99th percentile, generally in=20
an arc from the southern OR Cascades into the central/southern=20
Idaho ranges and into Wyoming. There, WSW to W flow will maximize=20 accumulations over parts of the Bitterroots and especially into the
Tetons, Absarokas, and Wind River Range. WPC probabilities for at=20
least 24 inches of snow over the three-day period are high (>70%)=20
over central Idaho and especially western Wyoming. High mountain=20 peaks/ridges above 9000-10,000ft may see several feet of snow=20
before precipitation begins to wane on Tuesday in response to=20
building heights along/east of the Divide.


*** Strong Atmospheric River to impact California and the Sierra=20
Nevada over the next several days ***

...Sierra Nevada...
Days 1-3... Maximum impact level from WSSI: Major to Extreme

A long-lived Atmospheric River event will contain periods of=20
precipitation as embedded systems move inland from the Pacific over
the next several days (and beyond). A few areas of surface low=20
pressure have and will move inland across NorCal today/tonight and=20
will continue to bring heavier snow to the northern/central Sierra=20
into early Monday with snow levels around 8000-10,000ft from north=20
to south. Snow may impact some of the passes across the Sierra=20
Crest though the heaviest snow rates may be above 9000ft (2-3"/hr).
Monday night/early Tuesday, the moisture plume will lift northward
with less accumulation overall (except for the highest peaks in=20
the Shasta/Siskiyous and farthest north Sierra) as another system=20
in the Pacific deepens. This will allow the initial plume to weaken
a bit over NorCal into southern Oregon while the next surge of=20
moisture pushes into central CA in response to height falls just=20
off the West Coast. This will target most of the Sierra by early=20
Wednesday with increasingly heavier snow and snow rates (2-4"/hr=20
near the Crest) above 8000ft that will fall as the AR progresses=20
slowly southeastward.=20

For days 1-2, WPC probabilities for at least 12 inches of snowfall
are >50% above around 8000ft. For day 3 alone, with the next=20
strong moisture surge, WPC probabilities for at least 12 inches of=20
snow are >50% above 8000ft with >70% probabilities for at least 18=20
inches of snow above 9000ft. This very active and impactful weather
pattern across California is expected to continue through much of=20
this week, with additional high elevation heavy snow likely into=20
the end of this week. See our latest Key Messages that cover the=20
event through the end of next week, and CPC's Key Messages into=20
week 2.


The probability of significant icing is less than 10 percent.=20

Fracasso/Snell

...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8YxyrDcVV2VjIHL52sTTCq9ZhLfybUScoUs9uTHV_nFoe= rz6D4vv4aCmjAfBzmSyI8UdxqgSYNSrs-zGtj35CF7gC7Q$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 220827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EST Mon Dec 22 2025

Valid 12Z Mon Dec 22 2025 - 12Z Thu Dec 25 2025


...Northeast...
Days 1-3... Maximum impact level from WSSI: Minor to Moderate

Upper level pattern over CONUS by the end of Day 1 includes an=20
anomalous ridge centered over the central U.S. and strong jet=20
soaring to the north along the U.S-Canadian border before aiming=20 southeastward across the Northeast, where slight troughing remains.
An embedded shortwave crossing north of the Great Lakes on Tuesday
within a divergent left-exit region of a strengthening 150kt jet=20
streak will aid in blossoming precipitation across the Northeast by
early Tuesday. Broad WAA ahead of the system over the still cold=20
Northeast (especially just inland) will bring generally light snow=20
to much of the Northeast and northern Mid-Atlantic, but some light
freezing rain on the southern edge of the precipitation shield=20
(central PA and perhaps into parts of WV). The highest QPF=20
associated with the strongest low-level WAA will lie over=20 Northern/Upstate/Central NYS into central New England as the=20
surface warm front lifts into the region. With the fast flow, the=20
parent low over Canada will get left behind as the front occludes=20
and stretches across New England, ultimately forming a new low in=20
the Gulf of Maine. This will likely lead to a separate and higher=20
maximum in QPF due to an inverted trough or quickly developing=20
TROWAL maximizing snow potential across southern/coastal Maine, but
some uncertainty remains with the details as this trough could=20
still shift somewhat east or southwest along the Gulf of Maine.=20
This setup has the potential to produce a narrow corridor of very=20
heavy snowfall given the strong low- level convergence potential=20
from roughly Portland to Bar Harbor, ME. In fact, the NBM 75th=20
percentile currently sits around 12 inches, highlighting the higher
end potential. The system will pull away from eastern New England=20
late Wednesday afternoon.

WPC probabilities for at least 4 inches of snow are >50% over=20
portions of the Finger Lakes region northward to the Tug Hill and=20 Adirondacks, Green Mountains, and into the White Mountains and=20
Maine Midcoast. The highest probabilities (40-70%) for at least 6=20
inches of snow extend between the southern and midcoasts of
Maine. The National Weather Service in Gray, ME has issued Winter=20
Storm Watches in this region for the potential for total snow=20
accumulations greater than 6 inches. Lighter, festive snowfall is=20
expected elsewhere in New England on Tuesday and even as far south=20
as northeast PA/northern NJ for the Tuesday morning commute.


...Interior West & Rockies...
Days 1 & 3... Maximum impact level from WSSI: Moderate to Major

Heavy snowfall continues to impact the high terrain of the Rockies
and Intermountain West, but will see the overarching pattern begin
to shift away from the recent west-east oriented Atmospheric River
spillover towards more southerly flow and approaching height falls
by midweek. With that said, the Day 1 period starts with the
aforementioned AR and anomalous PWs extending from the northern
Sierra Nevada into the Northern Rockies, but this moisture stream
is expected to wane today as an associated shortwave ejects
eastward with ridging building in its place across the Rockies
through Tuesday. Snow levels will remain high within the axis of
greatest precipitation located across central ID into southwest MT
and western WY, with levels generally in the 7000-8000ft range. The
most impact snowfall with amounts measured in feet continue to be
located across the Wind River Range, Tetons, and Absarokas.

A brief lull in heavy snowfall is expected on Tuesday as IVT
weakens and reorients into a more north-south direction into the
northern Great Basin as height falls approach the West Coast.
However, by Day 3 a broad surge of tropical moisture lifts
throughout the interior West due to a near-record deep upper trough
off the West Coast. Given the moisture source it isn't too
surprising that snow levels across the Great Basin and Rockies will
be rather high, above 9000ft in Utah and above 10,000ft in western
Colorado, with slightly lower values around 7000-8000ft in the
Northern Rockies during this time period.

WPC 72-hr snowfall probabilities for at least 12 inches of snow are
highest across the Sawtooths of ID and Wind River/Absarokas of WY,
with 70-90% chances mainly above 8500ft.


*** Strong Atmospheric River to impact California and the Sierra=20
Nevada over the next several days ***

...Sierra Nevada/Northern California/Cascades...
Days 1-3... Maximum impact level from WSSI: Major to Extreme

A long-lived Atmospheric River event will contain periods of=20
precipitation as embedded systems move inland from the Pacific over
the next several days (and beyond). For Day 1 (ending 12Z Tuesday),
the ongoing AR will lift north into northern CA and weaken with
limited snowfall impacts across CA. Meanwhile, much lower snow
levels and a potent shortwave entering southeast British Columbia
will allow for heavy snow across the Olympics and Cascades today
into early Tuesday. Here, snow levels will vary between
1500-2000ft, which puts accumulating snow below the major WA
Cascade passes.

By late Day 2 into Day 3, the next surge of moisture impacts the
West Coast and continues beyond into late this week. Deepening
height falls off the West Coast and a potent shortwave lifting on
the eastern periphery of this deep upper trough rapidly surges
moisture inland Tuesday night. IVT directed into the Sierra will be
strong (>800 kg/m/s) Tuesday night, but relatively short-lived as
broad onshore flow and moderate precipitation continues on Day 3.
Snow levels during this strong AR are expected to generally remain
around 8000ft (closer to 8500ft in the core of the AR across the central/southern Sierra Nevada), but quickly fall to between
5000-6500ft (lower north and higher south) across CA on Day 3.=20
This will allow for heavy snow to impact all major passes by=20
Wednesday.

For the most impactful day (Day 3) WPC probabilities for at least=20
12 inches of snowfall are 70-99% above around 7000ft and >70% for=20
at least 24 inches of snowfall above 8000ft in the Sierra Nevada.=20
Strong winds combined with very heavy-wet snowfall could make=20
travel difficult to impossible at times in the high terrain of the=20
Sierra Nevada, with damage to infrastructure also possible. This=20
very active and impactful weather pattern across California is=20
expected to continue through much of this week, with additional=20
high elevation heavy snow likely into the end of this week. See our
latest Key Messages that cover the event through the end of next=20
week, and CPC's Key Messages into week 2.


The probability of significant icing is less than 10 percent.=20

Snell


...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!4Zad0Gdrr51OXkfTGAdILviKN5pcYLPC0kOOau9ldhSpK= c8rBebO9pfTYNjHgGi_HaSZmFTnH2fhUaUDCBGGcnbudQc$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 222058
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
358 PM EST Mon Dec 22 2025

Valid 00Z Tue Dec 23 2025 - 00Z Fri Dec 26 2025

*** Strong Atmospheric River followed by low pressure systems to=20
impact California and the Sierra Nevada through Friday ***


...Northeast...
Days 1-2... Maximum impact level from WSSI: Moderate

A shortwave trough crosses northern Ontario Tuesday and New England
Tuesday night on a potent 150+kt NWly jet below a deep and
sprawling vortex centered north of Hudson Bay. Precip blossoms=20
late tonight in warm air advection over the upper Ohio Valley and
the Northeast Tuesday. Day 1 snow probs for >4" are 30-60% for the
Catskills west toward the Finger Lakes and the southern slopes of
the Adirondacks. Light freezing rain (a few hundredths accretion)=20
on the southern edge of the precipitation shield (from central PA=20
to central WV) is possible late tonight into Tuesday morning.=20

The surface low crosses New England Tuesday evening with continued
snow for Tuesday night in terrain including the Whites, Greens and
Adirondacks as the WAA pivots to deformation banding with=20
topographic enhancement (which should boost snow rates into the=20
1"/hr range) on the back side of the low. Day 1.5 snow probs for=20

6" are 30-80% over this terrain with 50% probs for over 8" in the=20

highest terrain.=20

Most of Maine is north of the surface low track which will have=20
ocean enhanced snow Tuesday night before the back side banding=20
shifts down the coast to produce ocean enhanced snow for eastern=20
Mass Wednesday morning. Day 2 probs for >6" are 40-70% for much of
the central Maine coast west well into the remote interior
portions of the state.


...California/Sierra Nevada...=20
Days 2-3... Maximum impact level from WSSI: Extreme

Atmospheric River (AR) over northern CA this afternoon pivots north
to OR and the northern Rockies tonight. High snow levels over
8000ft lift north with the core of highest precip from the
northern Sierra Nevada through the CA Cascades/Trinity Alps keeping
Day 1 quiet in CA from a snow perspective.=20

However, the now north-south oriented AR pushes across the CA coast
late Tuesday, reaching the full extent of the Sierra Nevada with=20
heavy precip and snow levels around 7000ft Tuesday evening with
particularly heavy snow starting roughly after midnight (with rates
exceeding 3"/hr per the 12Z HREF) above the snow level. Snow=20
levels drop under height falls from the approach trough through the
day Wednesday, though precip rates decrease on the Sierra Nevada=20
as the AR focuses over southern CA with 9000ft snow levels for the=20
SoCal ranges. Day 2 snow probs for >18" are 40% for the higher
central Sierra and 70-100% for the southern Sierra and the highest
White Mtns along the border with NV.

Expect a lull in Sierra Nevada snow Wednesday night as the dry=20
slot works its way across. However, by Thursday rates increase
again ahead of the upper trough axis. This time snow levels are
around 6000ft on the Sierra Nevada under the lower heights of an
upper low centered off northern CA. Snow rates of 2"/hr or more can
be expected for much of Thursday. Broader coverage of the >18"=20
snow probs are depicted for Day 3 with 50-90% values along the full
length of the Sierra Nevada as well as the CA Cascades including=20
Donner Pass on I-80.


Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below. CPC has further=20
KMs for next week.


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Major

Upper low that is directing AR into CA is centered over the Queen
Charlotte Sound (BC) and a reinforcing shortwave trough crosses
Vancouver Island by this evening bringing a round of moderate
precip to the WA Cascades this evening. Snow levels already down
around 2500ft drop to around 1800ft before rates decrease overnight
providing impactful snow well below pass level. Day 1 snow probs
for >6" are 40-60% roughly at pass level in western WA, but it's
really all for this evening.=20

AR across northern CA to western WY this afternoon pivots=20
north to southern OR to the Bitterroots through Tuesday. Snow
levels rise in this moisture axis to around 7000ft keeping Day 1
snow probs for >6" limited to the highest Sawtooths, Tetons, and=20
Absarokas. The AR continues to pivot north-south along the West=20
Coast through Tuesday night with snow levels rising above 4000ft on
the WA Cascades by Wednesday. Day 2 snow probs for >4" are 40-60%=20
in the WA Cascades.

The focus for precip shifts interior on Wednesday as the AR
extending the length of CA shifts east over the Great Basin and the
Rockies for Wednesday night/Thursday. Snow levels are generally
high, 8000-9000ft with this moisture shield shifting inland. Day 3
snow probs for >6" are limited to the highest Great Basin ranges,
the Sawtooths, Uinta, Wind River, and San Juans where values are
40-70% (80% or greater for the higher Wind Rivers).=20


Jackson



...Atmospheric River/Winter Storm Key Messages are in effect for
California as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-VZ02Vbi2p7uqvUSbXIOQH-rdR7tvmWmepI6Nz0W1prv3= DGPmRKbpBHln8TEYs5vFPhnIwL8EQ9CGVhJtRgt-JyXbTM$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 230833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
333 AM EST Tue Dec 23 2025

Valid 12Z Tue Dec 23 2025 - 12Z Fri Dec 26 2025

*** Strong Atmospheric River followed by low pressure systems to
impact California and the Sierra Nevada through Friday ***


...Northeast...
Days 1-2... Maximum impact level from WSSI: Moderate

A shortwave trough crosses northern Ontario today and New England=20
early Wednesday on a potent 150+kt NWly jet below a deep and=20
sprawling vortex centered north of Hudson Bay. Precip will be
ongoing this morning in warm air advection over the upper Ohio=20
Valley and the Northeast. Surface temperatures become marginal
quickly after sunrise and limits the potential for heavy
accumulations from PA to southern New England. Light freezing rain
(a few hundredths accretion) is also possible this morning on the=20
southern edge of the precipitation shield (from central PA to=20
central WV).

The surface low crosses New England this evening with continued=20
snow into Wednesday morning for the terrain including the Whites,=20
Greens and Adirondacks as the WAA pivots to deformation banding=20
with topographic enhancement (which should boost snow rates into=20
the 1"/hr range) on the back side of the low. Day 1 snow probs for

6" are 40-80% over this terrain with 50% probs for over 8" in the

highest terrain.=20

Heaviest snowfall associated with this system is expected across
the coastal plain and areas just inland across Maine as low
pressure redevelops along a surface trough over the Gulf of Maine.
This surface trough, or also referred to as a "Norlun Trough", will
lead to very strong and narrow low-level convergence capable of
producing snowfall rates of 1-2"/hr. However, given the narrow axis
these setups can be extremely tricky to forecast. Current
expectations are for heavy snow to occur between Portland and Bar
Harbor, along with areas just inland. Surface temperatures could
also be a concern for regions right along the coast as southerly=20
flow draws both moisture and a slightly warmer marine airmass. Days
1-2 probs for >8" are 50-80% for much of the central Maine coast=20
west well into the remote interior portions of the state. Maximum
amounts within the heaviest band are likely to exceed a foot, which
is depicted in the NBM 75th percentile for areas just inland of the
coastal plain.


...Great Lakes...
Day 3... Chances of at least minor impacts from WSSI-P: 40-50%

By late in the forecast period (Thursday night), the next shortwave
to round the top of the anomalous central U.S. upper ridge begins
to cross over the Northern Plains and Upper Midwest. Even though
the system is fairly unorganized through early Friday morning, the
origins of the shortwave and associated mid-to-upper level moisture
trace back to the tropical Pacific and Atmospheric River set to
impact California. In fact, NAEFS ESAT depict IVT above the 99.5th climatological percentile Thursday evening over the western Great
Lakes. Still, the greatest forcing at this time appears along the
MN-Canadian border and just north into Canada, limiting snowfall
impacts. However, a potent warm nose around 800mb per model cross
sections will allow for precipitation throughout parts of the=20
Upper Midwest and Great Lakes to fall as sleet or freezing rain. As
850mb FGEN rapidly strengthens across southern MI Friday morning=20
in response to a developing low pressure center over the Midwest,
precipitation is expected to blossom and fall mostly as sleet or
freezing rain. WPC probabilities for at least 0.1" of ice accretion
through 12Z Friday (more possible afterwards as well) are currently
low (10-20%) across the central L.P. of MI. Expect higher chances
once all of Friday is in the forecast period.


...California/Sierra Nevada...=20
Days 1-3... Maximum impact level from WSSI: Extreme

Strong Atmospheric River is set to impact CA during the Day 1
period with heavy snowfall across the Sierra Nevada. Additional
systems containing heavy high elevation snow and falling snow
levels are expected through the end of the week. In total, multiple
feet of snowfall are expected along the entire Sierra Nevada
(heaviest in central and southern sections), with snowfall also
impacting most major passes into northern CA.

The meteorological setup for this significant event includes a
currently north-south oriented AR combining with a potent shortwave
lifting along the WEst Coast today while on the eastern periphery
of an anomalous eastern Pacific upper trough. This shortwave and
associated potent surface low pressure will draw moisture northward
out of the tropics and produce IVT above the climatological record
for late December according to the NAEFS ESAT by early Wednesday.=20 Additionally, snow levels start out Tuesday night between
7500-8500ft across CA (highest in the southern Sierra) and fall to
below 6000ft in northern CA by Wednesday night as levels dip to
around 7500ft in the southern Sierra. Where snow does occur across
the Sierra Nevada it will come down extremely heavy as 00z HREF
depicts rates greater than 2-3"/hr after 09Z Wednesday and lasting
into Wednesday evening. Snow levels continue to drop under height=20
falls from the approaching trough through Wednesday night into=20
Thursday though as precip rates decrease on the Sierra Nevada as=20
the AR focuses over southern CA with 9000ft snow levels for the=20
SoCal ranges. This will lead to a dry slow until the next surge
ahead of a separate Pacific low approaches on Thursday.

By Thursday rates increase again ahead of the upper trough axis.=20
This time snow levels are around 6000ft on the Sierra Nevada under=20
the lower heights of an upper low centered off northern CA. Snow=20
rates of 2"/hr or more can be expected for much of Thursday.=20
Broader coverage of the >18" snow probs are depicted for Day 3 with
50-90% values along the full length of the Sierra Nevada as well=20
as the CA Cascades including Donner Pass on I-80. Snow levels also
drop to around 4000ft by the end of Day 3 across northern CA and
allow for accumulating snow potential for the I-5 pass near Mount
Shasta. 72-hr snow probabilities for >30" snow are between 50-90%=20
for much of the Sierra Nevada. Totals are likely to exceed 4-8 feet
above 7000-8000ft.


Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below. CPC has further=20
KMs for next week.


...Pacific Northwest, Great Basin and Rockies...=20
Days 2-3... Maximum impact level from WSSI: Moderate=20

Outside of light snow across the northern Great Basin and Cascades
on Day 1, the next surge of moisture is forecast to enter the
interior West and Northwest ranges on days 2-3. The strong AR=20
extending the length of CA shifts east over the Great Basin and the
Rockies for Wednesday night/Thursday along with its anomalous
moisture. Snow levels are generally high, 8000-9000ft with this=20
moisture shield shifting inland outside of the Cascades where=20
levels increase to 5000ft Wednesday and drop back to around 3000ft=20
Thursday. Days 2-3 snow probs for >6" are limited to the highest=20
OR/WA Cascades, Great Basin ranges, the Sawtooths, Uinta, Wind=20
River, and San Juans where values are 40-70% (80% or greater for=20
the higher Wind Rivers and Sawtooths).=20


Snell/Jackson




...Atmospheric River Key Messages are in effect. Please see=20
current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-I0_CPZ0UePHURDQNcl63Rb55rx8NtluQA6D4C_6vmtRL= qm2ELNT0ODX-yKMq99rSkPeDFD40nbB7L0gE6JKjNo8YlM$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 231852
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
152 PM EST Tue Dec 23 2025

Valid 00Z Wed Dec 24 2025 - 00Z Sat Dec 27 2025

*** Strong Atmospheric River followed by low pressure systems to
impact California and the Sierra Nevada through Friday ***


...Northeast...
Days 1 & 3-3.5... Maximum impact level from Day 1 WSSI: Major. Day
3-3.5 WSSI-P Minor Maximum Probabilities: 90%.

A sharpening 500mb shortwave trough in southern Ontario heads towards
the Northeast U.S. this afternoon as the diffluent left-exit region
of a roaring 150kt 300mb jet streak adds healthy divergence atop
the atmosphere. A ribbon of 850-700mb WAA and resulting FGEN is
responsible for the ongoing shield of snow across the Northeast
today and, once it becomes quasi-stationary over eastern MA on
north to the Gulf of Maine, will become the defacto train-tracks
for the 850mb low as it tracks from the St. Lawrence Valley tonight
to off the MA Capes by Christmas Eve morning. Periods of snow will
continue, falling heavily at times tonight, from the Adirondacks=20
and the rest of the northern New England mountains, on east to the=20
coast of Maine as the 850mb low strengthens and a Nor-lun trough fosters
heavy snow north and east of Portland. Burst of heavy snow cannot=20
be ruled out as far south as the MA Capes on Wednesday, but the=20
deepening storm system south of Nova Scotia will quickly race east=20
and all but end any accumulating snowfall by mid-afternoon. WPC=20 probabilities show east-central ME as having >50% odds for snowfall
totals >8" through Wednesday afternoon. The WSSI generally shows=20
Moderate Impacts from the Portland area on north and east along the east-central ME coast with localized Major Impacts in areas where
snowfall totals exceed 12". WPC probabilities also depict high=20
chances (>70%) for snowfall totals >4" in portions of the=20
Adirondacks, Green, and White Mountains, as well as much of=20
interior ME. WSSI shows widespread Minor Impacts from this=20
snowfall, implying some inconveniences to travel are likely with=20
winter driving conditions. Those traveling today and Christmas Eve=20
in the interior Northeast should use caution while driving in these
areas.

In wake of a fast moving clipper system over northern New England
on Christmas Day, strong 850mb CAA ahead of a strengthening dome of
Canadian high pressure will result in a cold-air-damming signature
(CAD) to become positioned briefly over the Northeast by Friday
morning. To the west, a progressive 500mb shortwave trough over the
Great Lakes will approach and strong 850mb WAA will accompany
sufficient 290K isentropic ascent to produce precipitation over the
Northeast. Healthy mid-to-upper level ascent will also be supplied
in the form of healthy 700mb Q-vector convergence Friday afternoon
and evening. This classic "over-running" setup with a burgeoning
warm nose of >0C air at low-levels but sub-freezing wet-bulb
temperatures at the surface (due to a cold and very dry boundary
layer at the onset) will allow for an icy wintry mix of
sleet/freezing rain to fall from western PA and northern MD on east
across southern PA and towards the Delaware Valley. Meanwhile,
areas farther north of the storm track and areas with more=20
elevation; such as northern PA, the Poconos, NY Finger lakes,
Catskills, northern NJ, and potentially the NYC metro on north and
east through southern New England, are showing better odds of
remaining mostly snow for Friday afternoon and into Friday night.

Through 12Z Saturday, WPC probabilities show low-to-moderate chances
(20-50%) for snowfall totals >4" in northeast PA, southern NY,=20
northern NJ, western MA, and western CT. Meanwhile, WPC ice=20
probabilities show moderate-to-high chances (50-70%) for ice=20
accumulations over a tenth of an inch along the Laurel Highlands=20
and central Appalachians. The same mountain ranges also show
moderate chances (>50%) for ice accumulations greater than a
quarter inch. Light ice accumulations and some accumulating sleet
is expected as far east as northern MD, southern PA, and the
DC/Baltimore metro areas. There remains ongoing fluctuations in=20
the forecast track which could result in additional changes in=20
which areas see the most snow and ice. Regardless, WPC's WSSI-P=20
show >50% odds for Minor Impacts from western PA to as far east as=20
the Tri-State area between 1AM Fri - 1AM Sat. Residents and=20
travelers following Christmas will want to keep a close eye on this
forecast over the next couple of days.


...Great Lakes...
Days 2.5-3... Maximum chances of at least minor impacts from=20
WSSI-P: 70%

An impressive plume of Pacific and subtropical moisture ejecting=20
out of the robust longwave trough off the West Coast will travel=20
around the northern periphery of the ridge axis over the south-
central U.S. and head for the Great Lakes on Thursday. Guidance is
in agreement on strong 850-700mb WAA over the north-central U.S.
Thursday afternoon with a band of snow developing along the 700mb
front. This is likely to result in a combination of snow and some
embedded sleet/freezing rain across northern ND and northern MN
Thursday night, then across northern WI and the U.P. of MI early
Friday morning. The strong but transient 850-700mb WAA will cause a
stout warm-nose of >0C temperatures over MI that cause a wintry mix
to engulf much of Michigan's Mitten on Friday, with the same icy
potential just east of Lakes Erie and Ontario Friday afternoon. The
progressive nature of this disturbance will help to cap snowfall
totals to generally <4", with the lone exceptions being the MN=20
Arrowhead and northern half of MI's U.P. where WPC probabilities=20
how low-to-moerate chances (20-50%) for snowfall totals >4".
Otherwise, ice is of concern across central and southern MI,
northeast OH, northwest PA, and far eastern NY. WPC probabilities
show moderate-to-high chances (50-70%) for ice accumulations of at
least one-tenth of an inch in these areas on Friday, including the
greater Detroit metro area. There are also low-chance
probabilities, of a more impactful event with over one-quarter of
an inch. WSSI-P shows the tip of the MN Arrowhead having moderate=20
chances (40-60%) for at least Minor Impacts due to snowfall from=20
this system, while central and southern MI sport moderate-to-high=20
chances (50-70%) for Minor Impacts due to ice.


...California/Sierra Nevada...=20
Days 1-3... Maximum impact level from WSSI: Extreme

The next Atmospheric River (AR) pushes across the CA coast
tonight, with heavy precipitation suddenly reaching the=20
central/southern Sierra Nevada around midnight with 3-4"/hr rates
(per the 12Z HREF) above the snow levels of 7500ft/8500ft through=20
the heaviest precip Wednesday morning. Snow becomes more showery=20
with moderate rates and lower snow levels of 6500/7500ft Wednesday=20 afternoon/night in the continued southerly flow behind the main AR=20
plume. The next moisture plume arrives early Thursday morning with=20
snow levels around 6000ft and heavy snow rates of 2-3"/hr into the=20
afternoon before rates decreased a bit in showery conditions and=20
snow levels dipping below 5000ft through Friday morning.=20

These rounds of heavy snow with lowering snow levels will lead to=20
increasing travel and infrastructure impacts. Storm total snowfall=20
in excess of 4ft can be expected above 6500ft along the extent of=20
the Sierra Nevada.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect
heavy snow above 7000ft tonight and above 5000ft Wednesday
afternoon through Thursday. Moderate snow above 4000ft can be
expected Thursday night through Friday as low pressure lingers near
Cape Mendocino. Some snow impacts to I-5 near Mt Shasta are
possible.

Snow levels remain around 10,000ft in Southern CA through the main
AR plume Wednesday before dropping to around 7000ft Wednesday night
into Friday. Impactful snow looks to remain higher than Big Bear
Lake.=20


Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below. CPC has Key
Messages for the Pacific Northwest into California through early=20
January.


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate=20

The remnant first AR, with an axis from far northern CA to western
MT this afternoon, continues lifting north as surface low pressure
rides along from SW OR up the Cascades tonight into Wednesday. Snow
levels rise on the WA Cascades from around 3000ft this evening to
4000ft by 12Z Wednesday. Moderate snow rates around 0.5"/hr can be
expected through Wednesday morning above those snow levels on the=20
WA Cascades. Day 1 PWPF for >4" above pass level are 40-80%.=20

The next AR surges through CA tonight and across the Great Basin
Wednesday, reaching the western Rockies Wednesday night. Snow=20
levels are high in this moisture shield, 8000-9000ft over the Great
Basin and the Rockies through central ID and WY with much lower=20
precip and snow levels of 6000-7000ft in northern ID and MT. Day=20
1.5 snow probs for >6" are 40-80% in the highest central NV ranges,
the Sawtooths, Wind Rivers, and Uintas.=20

The following moisture surge through CA Thursday brings widespread
precip at lower rates than before across the Great Basin and=20
western Rockies with lower snow levels around 6000-7000ft. Day 2.5
snow probs for >6" are 30-70% again for the highest central NV ranges,
the Sawtooths, Wind Rivers, Uintas, as well as western CO ranges
and the Absarokas.

The upper trough comes ashore Friday in northern CA up through the
PacNW with moderate precip rates and Cascades snow levels around=20
2500ft in WA and 3500ft in OR. Day 3 snow probs for >6" are 40-70%
in the WA Cascades, including Snoqualmie Pass, and around 30% for
the OR Cascades including Santiam Pass. Snow will continue in
earnest for the Rockies into Saturday.


Mullinax/Jackson



...Winter Storm/Atmospheric River Key Messages are in effect and
linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!748M92R3xI_pv1iK1Rxjk-4CcKjFg89ad5izP-Qu4FuJA= U0nVasQbx7qHo4hN9wCFbI8WQwj7qA1HBLzwHvxS0diFjc$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 240846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EST Wed Dec 24 2025

Valid 12Z Wed Dec 24 2025 - 12Z Sat Dec 27 2025

*** Strong Atmospheric River followed by low pressure systems to
impact California and the Sierra Nevada through Friday ***


...Maine...
Day 1... Maximum impact level from WSSI: Moderate

Heavy snow is expected to continue from overnight along a narrow=20
section of the Midcoast and interior sections of Maine for the=20
first part of Day 1 as a surface (Norlun) trough remains in place.=20
Over 6 inches of snow had already been reported within this band=20
over the coastal plains northeast of Portland as of 05Z. Heavy=20
snowfall with rates around 1-2"/hr are expected to continue through
at least 15Z as this mesoscale areas of low pressure form and=20
pivot within this surface trough. Once this area of low pressure=20
begins pivoting southward, snowfall should quickly ease in=20
intensity. WPC probabilities for an additional 4 inches of snow=20
after 12Z today are 20-40% from Portland east along the Midcoast,
but not after upwards of a foot of storm total snowfall occurs
across the region.


...Great Lakes to Northeast...
Days 2-3... Maximum impact level from WSSI: Moderate

An impressive plume of Pacific and subtropical moisture ejecting=20
out of the robust longwave trough off the West Coast will travel=20
around the northern periphery of the ridge axis over the south-
central U.S. and head for the Great Lakes Thursday night before
reaching the northern Mid-Atlantic/Northeast on Friday-Friday
night. Guidance is in agreement on strong 850-700mb WAA over the=20
north- central U.S. Thursday afternoon with a band of snow=20
developing along the 700mb front. This is likely to result in a=20
combination of snow and some embedded sleet/freezing rain across=20
northern ND and northern MN Thursday night, then across northern WI
and the U.P. of MI early Friday morning. The strong but transient=20
850-700mb WAA will cause a stout warm-nose of >0C temperatures over
MI that cause a wintry mix to engulf much of Michigan's Mitten on=20
Friday, with the same icy potential just east of Lakes Erie and=20
Ontario Friday afternoon. The progressive nature of this=20
disturbance will help to cap snowfall totals to generally <4", with
the lone exceptions being the MN Arrowhead and northern half of=20
MI's U.P. where WPC probabilities show moderate chances (40-70%)=20
for snowfall totals >4". Otherwise, ice is of concern across=20
central and southern MI, where WPC probabilities show moderate-to-=20
high chances (50-80%) for ice accumulations of at least one-tenth=20
of an inch in these areas on Friday, including the greater Detroit=20
metro area. There are also up to 40% chances for a more impactful=20
event with over one- quarter of an inch.

In wake of a fast moving clipper system over northern New England
on Christmas Day, strong 850mb CAA ahead of a strengthening dome of
Canadian high pressure will result in a cold-air-damming signature
(CAD) to become positioned briefly over the Northeast by Friday
morning. To the west, a progressive 500mb shortwave trough over the
Great Lakes will approach and strong 850mb WAA will accompany
sufficient 290K isentropic ascent to produce precipitation over the
Northeast. Healthy mid-to-upper level ascent will also be supplied
in the form of healthy 700mb Q-vector convergence Friday afternoon
and evening. This classic "over-running" setup with a burgeoning
warm nose of >0C air at low-levels but sub-freezing wet-bulb
temperatures at the surface (due to a cold and very dry boundary
layer at the onset) will allow for an icy wintry mix of
sleet/freezing rain to fall from western PA and northern MD on east
across southern PA and towards the Delaware Valley. Given the warm
nose elevated in model cross sections to around 800-750mb, a deep
cold layer below it could mean precipitation falling mostly as
sleet across the northern mid-Atlantic (northern MD,
southern/central PA, and into southern/central NJ). This may cut
down on snowfall and freezing rain accumulations here, but still
could lead to slippery travel. Meanwhile, areas farther north of=20
the storm track and areas with more elevation; such as northern PA,
the Poconos, NY Finger lakes, Catskills, northern NJ, and=20
potentially the NYC metro on north and east through southern New=20
England, are showing better odds of remaining mostly snow for=20
Friday afternoon and into Friday night.

Through 12Z Saturday, WPC probabilities show moderate chances=20
(40-70%) for snowfall totals >4" in northeast PA, southern NY,=20
northern NJ, western MA, and western CT. Greatest chances for at
least 6" of snowfall (30-50%) are across the Poconos and Catskills
of northeast PA and NY. Meanwhile, WPC ice probabilities show=20
moderate chances (50-70%) for ice accumulations over a quarter of=20
an inch along the Laurel Highlands and central Appalachians. This=20
amount of ice would have the potential to produce scattered tree=20
damage and power outages. Light ice accumulations and some=20
accumulating sleet is expected as far east as northern MD, southern
PA, and the DC/Baltimore metro areas. The Philadelphia metro could
see more snow than sleet/freezing rain, but some wintry mix=20
combination can be expected with high uncertainty on amounts at the
moment. There remains ongoing fluctuations in the forecast track=20
which could result in additional changes in which areas see the=20
most snow and ice. Regardless, WPC's WSSI-P show >50% odds for=20
Minor Impacts across a large region from western PA to as far east=20
as the Tri- State area between 1AM Fri - 1AM Sat. Residents and=20
travelers following Christmas will want to keep a close eye on this
forecast over the next couple of days.


...California/Sierra Nevada...=20
Days 1-3... Maximum impact level from WSSI: Extreme

The next strong and quick-hitting Atmospheric River (AR) is=20
entering CA early this morning, with heavy precipitation ongoing=20
across the central/southern Sierra Nevada by 12Z with 3-4"/hr rates
(per the 00Z HREF) above the snow levels of 7500ft/8500ft through=20
the heaviest precip midday today. Snow becomes more showery with=20
moderate rates and lower snow levels of 6500/7500ft Wednesday=20
evening/night in the continued southerly flow behind the main AR=20
plume. The next moisture plume arrives early Thursday morning with=20
snow levels around 6000ft and heavy snow rates of 2-3"/hr into the=20
afternoon before rates decreased a bit in showery conditions and=20
snow levels dipping below 5000ft through Friday morning.
Precipitation is expected to finally wane by Friday night into
early Saturday morning as upper-level ridging builds into the
eastern Pacific and the meandering upper low over CA weakens into a positively-tilted trough extending across the Great Basin.

These rounds of heavy snow with lowering snow levels through Friday
will lead to increasing travel and infrastructure impacts. Storm=20
total snowfall in excess of 4ft can be expected above 6500ft along=20
the extent of the Sierra Nevada.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect
heavy snow above 5000ft this afternoon through Thursday. Moderate=20
snow above 4000ft can be expected Thursday night through Friday as=20
low pressure lingers near Cape Mendocino. Some snow impacts to I-5=20
near Mt Shasta are possible.

Snow levels remain around 10,000ft in Southern CA through the main
AR plume Wednesday before dropping to around 7000ft Wednesday night
into Friday. Impactful snow looks to remain higher than Big Bear
Lake.=20


Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below.


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

Area of low pressure riding up the Pacific Northwest coastline
today will bring a surge of moisture and increasing snow levels.=20
Snow levels rise on the WA Cascades to 5000ft by 12Z this morning
and quickly fall back to around 3500ft by tonight, but also as
moderate precipitation ends. Moderate snow rates around 0.5"/hr=20
can still be expected through this morning above those snow levels
on the WA Cascades.

The aforementioned strong AR surging through CA and will also=20
spill into the Great Basin today, reaching the western Rockies=20
tonight. Snow levels are high in this moisture shield, 8000-9000ft=20
over the Great Basin and the Rockies through central ID and WY with
much lower precip and snow levels of 6000-7000ft in northern ID=20
and MT. Day 1 snow probs for >6" are 40-80% in the highest central=20
NV ranges, the Sawtooths, Wind Rivers, and Uintas.=20

The following moisture surge through CA Thursday brings widespread
precip at lower rates than before across the Great Basin and=20
western Rockies with lower snow levels around 6000-7000ft. Day 2=20
snow probs for >6" are 30-70% again for the highest central NV=20
ranges, the Sawtooths, Wind Rivers, Uintas, as well as western CO=20
ranges and the Absarokas.

The upper trough comes ashore Friday in northern CA up through the
PacNW with moderate precip rates and Cascades snow levels around=20
2500ft in WA and 3500ft in OR. Day 3 snow probs for >6" are 40-70%
in the WA Cascades, including Snoqualmie Pass, and around 30% for
the OR Cascades including Santiam Pass. Snow levels also fall
across much of the Great Basin and Rockies, with levels below
3000-4000ft in the northern Rockies and 5000-7000ft in the central
Great Basin and remaining around 7000ft in the central Rockies.
This allows for more widespread moderate snowfall from the ranges
of northern ID and northwest MT to northern UT, where WPC
probabilities on day 3 for >6" are 50-80% above the aforementioned
snow levels.


...North-Central Montana...
Days 1-1.5... Maximum impact level from WSSI: Minor

Freezing rain is likely and may exceed 0.1" across parts of north-
central MT the night of Christmas Eve into Christmas morning as the
strong moisture plume associated with today's CA AR attempts to
spill into the northern High Plains. IVT values across the interior
West above the 90th climatological percentile along with the
favorable left-exit region of a quickly traversing 130kt jet streak
will work to squeeze a few tenths of an inch of QPF (at most)
across a region with cold low-level air being reinforced by strong
high pressure to the northeast. WPC day 1.5 probabilities for at=20
least 0.1" of freezing rain are currently 20-50% across north-
central MT. This amount of freezing rain may not be enough for
impacts to infrastructure, but could lead to slippery holiday
travel.



Snell




...Winter Storm/Atmospheric River Key Messages are in effect.=20
Please see current Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-qtGErMs0aLaJ73UGP_o77Cl93lnVgZl3k0GZBYwfbYQ8= qonqKfKWUckd8fr9smCsFtAVUCrx9eG-X6WZR3axB_5YwI$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 242044
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 PM EST Wed Dec 24 2025

Valid 00Z Thu Dec 25 2025 - 00Z Sun Dec 28 2025

*** Continued Heavy Snow on the Sierra Nevada through Friday ***


...Great Lakes to Northeast...
Days 2-3... Maximum impact level from WSSI: Moderate

An impressive plume of Pacific and subtropical moisture ejecting=20
out of the robust longwave trough off the West Coast will traverse the
northern periphery of the ridge axis over the south-central U.S.=20
and head for the Great Lakes Thursday night before reaching the=20
northern Mid-Atlantic/Northeast Friday night. Guidance is in=20
agreement on strong 850-700mb WAA over the north-central U.S.=20
Thursday afternoon with a band of snow developing along the 700mb=20
front. This will result in a combination of snow and some embedded=20 sleet/freezing rain across northern ND and northern MN Thursday=20
night, then across northern WI and the U.P. of MI early Friday=20
morning. The strong but transient 850-700mb WAA will cause a stout=20
warm-nose of >0C temperatures over MI that cause a wintry mix to=20
engulf much of Michigan's Mitten on Friday, with the same icy=20
potential just east of Lakes Erie and Ontario Friday afternoon. The
progressive nature of this disturbance will help to cap snowfall=20
totals to generally <4", with the lone exceptions being the MN=20
Arrowhead and northern half of MI's U.P. where WPC probabilities=20
show moderate chances (40-70%) for snowfall totals >4". Otherwise,=20
ice is of concern across central and southern MI, where WPC=20
probabilities show moderate-to- high chances (50-80%) for ice=20
accumulations of at least one-tenth of an inch in these areas on=20
Friday, including the greater Detroit metro area. There are also up
to 40% chances for a more impactful event with over one-quarter of
an inch.

In wake of a fast moving clipper system over northern New England
on Christmas Day, strong 850mb CAA ahead of a strengthening dome of
Canadian high pressure will result in a cold-air-damming signature
(CAD) that becomes positioned briefly over the Northeast by Friday.
To the west, the same progressive 500mb shortwave trough over the=20
Great Lakes will approach and strong 850-700mb WAA will accompany=20
sufficient 290K isentropic ascent to produce precipitation over the
Northeast and Mid-Atlantic. Healthy mid-to-upper level ascent will
also be supplied in the form of healthy 700mb Q-vector convergence
Friday afternoon and evening. This strong mid-level convergence is
further bolstered by the region being located beneath the diffluent
left-exit region of a 110kt 300mb jet streak. Guidance is keying=20
in on a narrow area of strong 700mb FGEN and vertical velocities=20
directly beneath the 300mb jet streak's left-exit region over=20
northeast PA, the Southern Tier of NY, the Lower Hudson Valley,=20
Poconos and Catskills, and even as far south as the NYC metro area=20
Friday evening. It is here where snow is likely to remain the=20
primary precipitation type with potential for hourly snowfall rates

1"/hr.

Farther south, this classic "over-running" setup with a burgeoning
warm nose of >0C air at low-levels but sub-freezing wet-bulb=20
temperatures at the surface (due to a cold and very dry boundary=20
layer at the onset) will allow for an icy wintry mix of=20
sleet/freezing rain to fall from western PA and northern MD on east
across southern PA and towards the Delaware Valley. Model cross
sections and soundings continue to show a warm nose elevated=20
around 800-750mb, meaning as precipitation falls into a deep cold=20
layer between the surface and 850mb would force sleet to fall across
the northern mid-Atlantic (northern MD, southern/central PA, and=20
into southern/central NJ). This would cut down on snowfall and=20
freezing rain accumulations here, but still could lead to slippery=20
travel conditions Friday night and Saturday morning given some
guidance members show the potential for as much as 2" of sleet in=20
some locations where prolonged periods of sleet occur.

Through 12Z Saturday, WPC and NBM probabilities show moderate=20
chances (50-70%) for snowfall totals >6" in northeast PA, southern=20
NY, northern NJ, western MA, and western CT, and the NYC metro=20
area. Greatest chances for >8" of snowfall (around 30%) are across
the Poconos and Catskills of northeast PA and NY down into northern
NJ. On the flip side, WPC ice probabilities show moderate chances=20
(50-70%) for ice accumulations over a quarter of an inch along the=20
Laurel Highlands and central Appalachians. This amount of ice would
have the potential to produce scattered tree damage and power=20
outages. Light ice accumulations and accumulating sleet is=20
expected through southeast PA, the Balt-Wash metro areas and into
NJ/DE. The Philadelphia metro could see more snow than=20
sleet/freezing rain, but some wintry mix combination can be=20
expected that results in slick travel conditions through Saturday=20
morning. There remains ongoing fluctuations in the forecast track=20
which could result in additional changes in which areas see the=20
most snow and ice. Regardless, WPC's WSSI-P show >50% odds for=20
Minor Impacts across a large region from western PA to as far east=20
as the Tri-State area between 1AM EST Fri - 7AM EST Sat. Residents=20
and travelers following Christmas will want to keep a close eye on=20
this forecast over the next couple of days.


...California/Sierra Nevada...=20
Days 1-3... Maximum impact level from WSSI: Extreme

Extreme snow rates currently on the High Sierra will diminish=20
later this afternoon as the AR plume shifts to eastern Nevada.=20
Snow becomes more showery with more moderately heavy rates and=20
lower snow levels of 6000/7000ft by 00Z in the continued southerly
flow behind the main AR plume. The next moisture plume arrives=20
early Thursday morning with snow levels of 55000/6500ft and heavy=20
snow rates of 2-3"/hr through midday before rates again decrease in
showery conditions through the afternoon. The last larger punch of
moisture arrives Thursday evening with persistent snow levels of=20
5500/6500ft through the night before dropping to 5000ft for Friday
with continued moderately heavy rates (1-2"/hr). Precipitation is=20
expected to finally wane by Friday night as upper-level ridging=20
builds into the eastern Pacific and the meandering upper low over=20
far northern CA weakens into a positively-tilted trough that shifts
east across the Great Basin.

The lower snow levels and rounds of heavy snow through Friday will
lead to increasing travel and infrastructure impacts. Additional
snowfall in excess of 3ft can be expected above 6000ft along the=20
extent of the Sierra Nevada.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect
moderately heavy snow above 5000ft through tonight with snow levels
dropping to 4000ft on Thursday with the higher rates continuing
through Thursday night before easing through Friday as low=20
pressure lingering near Cape Mendocino finally shifts east. Some=20
snow impacts to I-5 near Mt Shasta are possible mainly early Friday.

Snow levels drop to around 7000ft tonight where they linger through=20
Friday. Impactful snow looks to remain higher than Big Bear Lake.=20

Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below.


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

The aforementioned strong AR plume shifting east from the Sierra
Nevada this afternoon will continue to shift over the Great Basin=20
and reach the western Rockies by this evening before the intensity
greatly diminishes overnight. Snow levels are high in this=20
moisture shield, 8000-9000ft over the Great Basin and the Rockies=20
through central ID and WY with much lower precip rates and snow=20
levels of 6000-7000ft in northern ID and MT through tonight. Day 1=20
snow probs for >6" are 40-80% in the higher Sawtooths, Wind=20
Rivers, and Uintas, with 30-60% in the Absarokas, western CO
ranges, southern UT ranges, and highest central NV ranges.

The next moisture surge through CA early Thursday brings=20
widespread precip at lower rates than before across the Great Basin
and western and now northern Rockies with lower snow levels around
6000-7000ft Thursday night through Friday. Day 2 snow probs for=20

6" are 40-80% again for the Sawtooths, Wind Rivers, Tetons, and=20

Absarokas with 30-60% for the central NV ranges, Uintas, and
northern ID/western MT ranges.

The upper trough comes ashore over the Pac NW Friday with moderate
precip rates and Cascades snow levels around 2500ft in WA and=20
3500ft in OR. Day 2.5 snow probs for >6" are now 50-90% in the WA=20
Cascades, including Snoqualmie Pass, and 40-70% for the OR=20
Cascades including Santiam Pass. Snow levels also fall across much=20
of the Great Basin and Rockies on Friday, with levels below=20
3000-4000ft in the northern Rockies and 5000-7000ft in the central=20
Great Basin and remaining around 7000ft in the central Rockies.=20
This allows for more widespread moderate snowfall from the ranges=20
of northern/central ID and northwest MT to northern UT and western
WY, where WPC probabilities on day 2.5 for >6" are 50-80% above=20
the aforementioned snow levels.

The inland pushing trough axis will bring decent snows across the
northern and central Rockies Friday night/Saturday.


...Northern Montana...=20
Days 1-2... Maximum impact level from WSSI: Minor

Strong 850-700mb WAA and anomalous Pacific moisture overrunning a=20 sub-freezing boundary layer will provide a setup for freezing rain
tonight and into Christmas morning over northern MT though QPF is a
question. Surface temperatures will remain well below freezing=20
through 12Z Thursday while a burgeoning warm nose of >0C air=20
resides within the 850-750mb layer per CAMs soundings. While some=20
sleet may mix in at times, freezing rain will be the primary=20
concern through Christmas morning. Based on some soundings Thursday
afternoon, however, there is the potential for lingering freezing=20
fog across northeast MT and northwest ND. In fact, some model=20
members suggest prolonged moisture advection and sub-freezing temps
near the MT/ND and Canada border may keep freezing drizzle in the=20
forecast Christmas night and into Friday morning. WPC probabilities
show low chances (<30%) for ice accumulations over one-tenth of an
inch in north- central MT, but most accumulations will be less=20
than one- tenth across the northern tier of "Big Sky Country".=20
Expect potentially hazardous travel conditions across much of=20
north- central and northeast MT tonight and through Christmas=20
morning, as depicted by the Minor Impacts on the WSSI.


Mullinax/Jackson




...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!_TGyp3Ju54N-UcQ8HVhlEwuc26EkDO2dwLP3MMwRwDfNA= Wm2qQYg4ms8WStXcEBZSQHu0Z6O9E0XwoiDPybqQ-vgKIQ$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 250703
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
203 AM EST Thu Dec 25 2025

Valid 12Z Thu Dec 25 2025 - 12Z Sun Dec 28 2025

*** Continued Heavy Snow on the Sierra Nevada through Friday ***


...Great Lakes to Northeast...
Days 1-2... Maximum impact level from WSSI: Moderate

Quasi-zonal flow will direct a plume of moisture originating from=20
the West along the US/Canadian border today/tonight with WAA-driven
snow over the MN Arrowhead into the U.P. of Michigan. With cold=20
sub-32F sfc temps over parts of MN/WI/Lower MI at precip onset=20
tonight, some freezing rain is likely with minor accumulations over
MN/WI. WPC probabilities for at least 4 inches of snow are low to=20
moderate (20-60%) over the far northeastern MN Arrowhead into the=20
Keweenaw Peninsula.=20

Into D2, shortwave will push through northern Lower MI with its=20
sfc reflection over IN/OH and the 850mb low moving through BUF. The
sfc low will weaken as it approaches the Appalachians, getting too
far behind the mid-level shortwave, and ultimately jumping into=20
the Atlantic by 12Z Sat. From Friday to Saturday morning, a variety
of ptypes are expected over the region (central Appalachians/Mid-=20
Atlantic to the Northeast). The stubborn cold surface air will hold
tight over Lower MI and especially into the Laurel Highlands in=20
western PA where significant freezing rain is possible. WPC=20
probabilities of at least 0.10" icing are high (>70%) from around=20
Detroit and into western PA/western MD, with 40-60% probabilities=20
of at least 0.25" icing in these areas as well. Light icing is=20
likely on either side of this zone of maximum probabilities -- on=20
the south side along the I-66 corridor (DC) and into eastern WV. To
the north/northeast, deeper cold air at the surface will allow for
sleet to be a dominant ptype over central/eastern PA with up to an
inch of so possible. To the north, from central NYS through=20
northeast PA into the Catskills/Poconos and to the NYC Metro area,=20
an axis of moderate snow is possible, driven by the stronger height
falls at the nose of the incoming 130kt jet. The whole scenario is
still uncertain in where the transition zones align as some of the
00Z guidance (e.g., the NAM) were much farther northeast with the=20
WAA than the other global guidance. The recent trend has been=20
toward this milder scenario but only nudged the forecast somewhat=20
given the lead time still.=20

WPC probabilities for at least 4 inches of snow are >50% in a zone
bounded between I-890/Rt 17/I-476 to the west, the southern=20
Adirondacks on the north side, Berkshires/I-91 to the east, and=20
into the NYC Metro/Long Island to the south. Though the system will
be progressive, combination of higher SLRs and upslope could yield
more than 8 inches of snow into the southern Catskills.=20


...California/Sierra Nevada...=20
Days 1-3... Maximum impact level from WSSI: Extreme

The next moisture plume with the long-lived atmospheric river=20
event will arrive this morning into CA amid lower snow levels=20
around 55000-6500ft and heavy snow rates of 2-4"/hr through midday=20
before rates again decrease in showery conditions through the=20
afternoon. The last larger punch of moisture arrives this=20
evening/overnight with persistent snow levels of 5500/6500ft=20
through the night before dropping to 5000ft for Friday with=20
continued moderately heavy rates (1-2"/hr). Precipitation is=20
expected to finally wane by Friday night as the upper trough moves=20
ashore with ridging to follow. The lower snow levels and rounds of=20
heavy snow through Friday will lead to increasing travel and=20
infrastructure impacts. Additional snowfall of 2-5ft can be=20
expected above 6000ft along the extent of the Sierra Nevada.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect=20
moderately heavy snow above 4000ft or so as snow levels dip to=20
start the period. Some snow impacts to I-5 near Mt Shasta are=20
possible mainly early Friday. Most snow will end by 12Z Saturday.=20
Over SoCal, snow levels drop to around 7000ft tonight where they=20
linger through Friday. Impactful snow looks to remain higher than=20
Big Bear Lake.=20

Key Messages for the CA atmospheric river and subsequent low that=20
maintains impacts through Friday are linked below.


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

Though the AR affecting CA will infuse some moisture into the=20
Rockies, an incoming trough out of the Gulf of Alaska will drop=20
into the PacNW on Friday with a renewed increase of moisture to the
area as snow levels remain on the lower side -- generally=20
2500-3500ft in the Cascades. That trough will exit WA early=20
Saturday and bring widespread light to moderate snows to the=20
northern Rockies the CA AR (via the separate upper trough) moves=20
inland as well. This will act to expand the area of snow across=20
most of the Great Basin to central Rockies Saturday into early=20
Sunday before the entire full- latitude trough then exits onto the=20
Plains just beyond this forecast period. Snow levels will be much=20
lower over MT/ID and western WY compared to UT/CO (closer to the=20
warmer AR) -- generally 4000ft to the north (and falling to the=20
valley floors) ramping up to around 7000-8000ft over CO, falling to
below 6000ft by early Sunday morning.=20

For days 1-2, WPC probabilities for at least 12 inches are >50%=20
above about 2500ft in the WA Cascades (still affecting the passes),
5000ft in western MT, 6000ft in central ID, 7000-8000ft in the=20
western WY ranges, and about 9000ft in the Uintas. For days 2-3,=20
the focus will be on the CO Rockies where WPC probabilities for at=20
least 8 inches of snow are >50% above about 9000ft.=20


Fracasso


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9DtysQKcTuXQhxMcKfHeYjCpIeqFJmrWgTAvy3gKqa5WQ= 6_sMtVxVGdijBYGfI2ZZ8pAjxJzPTa_xFdkiKV4mKY6LGw$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!9DtysQKcTuXQhxMcKfHeYjCpIeqFJmrWgTAvy3gKqa5WQ= 6_sMtVxVGdijBYGfI2ZZ8pAjxJzPTa_xFdkiKV4LAyvh_8$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 251900
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
200 PM EST Thu Dec 25 2025

Valid 00Z Fri Dec 26 2025 - 00Z Mon Dec 29 2025

*** Continued Heavy Snow on the Sierra Nevada through Friday ***


...Great Lakes to Northeast...
Days 1-2... Maximum impact level from WSSI: Moderate

Quasi-zonal flow continues to direct a plume of moisture=20
originating from the West along the US/Canadian border=20
leading to WAA- driven snow over the MN Arrowhead into the U.P. of
Michigan. With cold sub-32F sfc temps over parts of MN/WI/Lower MI
at precip onset tonight, some freezing rain is likely with minor=20 accumulations over MN/WI. WPC probabilities for at least 4 inches=20
of snow are low to moderate (20-60%) over the Keweenaw Peninsula
into the eastern U.P.=20

Into D2, shortwave will push through northern Lower MI with its=20
sfc reflection over IN/OH and the 850mb low moving through BUF. The
sfc low will weaken as it approaches the Appalachians, getting too
far behind the mid-level shortwave, and ultimately jumping into=20
the Atlantic by 12Z Sat. From Friday to Saturday morning, a variety
of ptypes are expected over the region (central Appalachians/Mid-=20
Atlantic to the Northeast). The stubborn cold surface air will hold
tight over Lower MI and especially into the Laurel Highlands in=20
western PA where significant freezing rain is possible. WPC=20
probabilities of at least 0.10" icing are high (>70%) from central
to southeast MI, including Detroit, as well as into western=20
PA/western MD. 40 to 70% probabilities of at least 0.25" icing=20
exist over southeast MI down through northwest PA into the Laurel=20
Highlands. Light icing is likely on either side of this zone of=20
maximum probabilities -- on the south side along the I-66 corridor=20
(DC) and into eastern WV. To the north/northeast, deeper cold air=20
at the surface will allow for sleet to be a dominant ptype over=20 central/eastern PA with up to an inch of sleet possible.=20

To the north, from central NYS through northeast PA into the=20 Catskills/Poconos and to the NYC Metro area, an axis of moderate to
locally heavy snow is increasingly likely, driven by the stronger=20
height falls at the nose of the incoming 130kt jet. Beginning to=20
see numerical guidance fall in line on the axis of greatest=20
snowfall potential with the NAM shifting further south compared to=20
its placement at 00z. Rest of the dynamical guidance is keying on=20
the area from southern NY state down through the Lower Hudson to=20
NYC and 50-75 miles on either side seeing at least 4" with >6"
becoming a greater likelihood around the Catskills into the Lower
Hudson Valley to the north of NYC.=20=20

WPC probabilities for at least 4 inches of snow are still >50% in
a zone bounded between I-890/Rt 17/I-476 to the west, the southern
Adirondacks on the north side, Berkshires/I-91 to the east, and=20
into the NYC Metro/Long Island to the south. Probabilities for at
least 6" are now between 50-70% for that area of central NY state
down through southern NY, including the Catskills/Lower Hudson/NYC
corridor south and east of I-88. Though the system will be=20
progressive, combination of higher SLRs and upslope could yield=20
more than 8 inches of snow into the southern Catskills where areal
average maxima is currently positioned with some deterministic
indicating >10" on their outputs.

Fracasso/Kleebauer

...California/Sierra Nevada...=20
Day 1... Maximum impact level from WSSI: Extreme

*** Heavy Snow Continues on the Sierra Nevada through Tonight ***

The final round of widespread heavy snow arrives early this evening=20
to the northern Sierra Nevada then works its way down the length of=20
the Sierra Nevada through the overnight. Expect a few hours of 2-
3"/hr rates (per the 12Z HREF) above the snow level of 5000ft=20
(north/central Sierra) to 6000ft (southern Sierra) with an=20
additional 12-18" overnight.

Moderate snow showers continue into Friday evening with snow levels=20
dropping to 4500ft. The upper trough which had been offshore finally=20
shifts east to the Great Basin Friday night, cutting off Sierra snow=20
by 12Z Saturday.

Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect two=20
more rounds of heavy snow: this evening above 4000ft and early=20
Friday down to 3500ft. Snow impacts to I-5 near Mt Shasta are likely=20
Friday. Some moderate snow lingers Friday night before ending by 12Z=20 Saturday.=20

For SoCal, snow levels remain around 7000ft through Friday morning=20
and most of the additional precip. Snow levels do drop below 6000ft=20
Friday afternoon with some 1"/hr rate potential around Big Bear Lake=20
into the evening before tapering off.

Jackson

...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

Deep low pressure off CA will continue to infuse moisture across the=20
West with a separate trough pushing down the BC coast Friday and=20
over the northern Rockies Saturday providing a final focus for=20
precipitation and ending the active pattern.=20

Ongoing snow over the Cascades tapers off this evening with moderate=20
to locally heavy snow for the length of the Cascades Friday and=20
Friday night with snow levels dropping on the WA Cascades from=20
3000ft to 1000ft and over the OR Cascades to 2000ft. Day 1.5 snow=20
probs for >8" are 50-90% on the WA/OR Cascades including for the=20
Snoqualmie and Santiam passes.

The next round of moisture from CA arrives into the northern Rockies=20
this evening with prolonged moderate to heavy snow until the cold=20
frontal passage Friday night. Snow levels drop from 6000/7000ft to=20 3000/4000ft through this time leading to increasing travel impacts.=20
Day 1.5 snow probs for >8" are 50-80% over the Sawtooths, northern=20 ID/western MT ranges, western WY ranges, the higher central NV=20
ranges, and the Wasatch.

The progression of the cold front is notable with the Day 2.5 snow=20
probs for >8" limited to the Wasatch and 50-80% for northern and=20
western CO Ranges.

Jackson


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8i3BFfMTliwgu31BIOZxaNWLw-_P9c1QQwNBoXOUOClXz= ScdxcVlv1YeP0fW3SBOPRYYRBlFr9dsxT95BAZWTMW9e4E$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 260648
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
148 AM EST Fri Dec 26 2025

Valid 12Z Fri Dec 26 2025 - 12Z Mon Dec 29 2025

*** Continued Heavy Snow on the Sierra Nevada through Friday ***

*** Heavy Wintry Mix tonight through Friday night from the Great
Lakes through the Northeast and Mid-Atlantic ***

...Great Lakes to Northeast...
Days 1 & 3... Maximum impact level from WSSI: Moderate=20

Current UA analysis pin-points our shortwave that be involved in
the next winter focused disturbance over the northern and eastern
CONUS. Forecast is for the shortwave trough to push through=20
northern Lower MI with a sfc reflection developing over IN/OH this
morning. Major player in the forecast evolution will also be the
attendant 850mb low which will migrate over Lower MI, cutting east
to BUF leading to persistent southwesterly flow within the upper
portion of the boundary layer. The sfc low will weaken as it=20
approaches the Appalachians, getting too far behind the mid- level=20 shortwave, and ultimately jumping into the Atlantic by 12Z Sat.=20

=46rom Friday to Saturday morning, a variety of ptypes are expected=20
over the region (central Appalachians/Mid- Atlantic to the=20
Northeast) thanks to the WAA regime progged between 925-800mb. The
stubborn cold surface air will hold tight over Lower MI and=20
especially into the Laurel Highlands in western PA where=20
significant freezing rain is possible. WPC probabilities of at=20
least 0.10" icing are high (>70%) from central to southeast MI,=20
including Detroit, as well as into western PA/western MD. 40 to 70% probabilities of at least 0.25" icing exist over southeast MI down
through northwest PA into the Laurel Highlands. Light icing is=20
likely on either side of this zone of maximum probabilities -- on=20
the south side along the I-66 corridor (DC) and into eastern WV. To
the north/northeast, deeper cold air at the surface will allow for
sleet to be a dominant ptype over central/eastern PA with up to an
inch of sleet possible.=20

To the north, from central NYS through northeast PA into the=20 Catskills/Poconos and to the NYC Metro area, an axis of moderate to
locally heavy snow is likely, driven by the stronger height falls=20
at the nose of the incoming 130-135kt jet. 00z model suite is in
agreement on the axis of heaviest snowfall aligning over the area=20
from Central and Southern NY state down through the Lower Hudson=20
to NYC and 50-75 miles on either side seeing at least 4" with >6"=20
becoming a greater likelihood around the Catskills into the Lower=20
Hudson Valley to the north of NYC.=20

WPC probabilities for at least 4 inches of snow are still >50% in
a zone bounded between I-890/Rt 17/I-476 to the west, the southern
Adirondacks on the north side, Berkshires/I-91 to the east, and=20
into the NYC Metro/Long Island to the south. Probabilities for at
least 6" are now between 50-90% for that area of central NY state=20
down through southern NY, including the Catskills/Lower Hudson/NYC=20
corridor south and east of I-88. Though the system will be=20
progressive, combination of higher SLRs and upslope could yield=20
more than 8 inches of snow into the southern Catskills where areal=20
average maxima is currently positioned and latest WPC probabilities
for >8" now upwards of 40-70%.=20

On D3, another surface cyclone will intensify and move northeast
through the Upper Midwest and Great Lakes. Ensemble means show a
rapid CAA pattern within the northwest side of the cyclone leading
to snowfall breaking out across northeastern MN into northern WI
and the Michigan U.P. Best chance for at least 4" of snow lies over
the western U.P. due to lake effect threat kicking in downwind of
Lake Superior. WPC probabilities for >4" are now between 50-90%
across all of the central and western U.P. with the highest
probabilities across the Iron Range over into the Keweenaw
Peninsula.=20

Kleebauer


...California/Sierra Nevada...=20
Day 1... Maximum impact level from WSSI: Extreme

*** Heavy Snow Continues on the Sierra Nevada through this morning***

Final push of moderate to heavy snowfall forecast across the Sierra
Nevada today with the heaviest likely to occur this morning before
slowly waning as our AR event finally comes to an end. Prior,
expect heavy snow rates between 2-3"/hr at times leading to
additional accumulations between 1-2ft above 9000ft MSL. WPC
probabilities for >12" are still between 50-80% for much of the
northern and central Sierra Nevada with the highest probabilities
co-located with the area near Mammoth up to just south of I-80.
Storm totals will approach 4-6ft or more after the full event is
complete leading to significant impacts to travel even after the
event has completed.=20

Kleebauer


...Pacific Northwest, Great Basin and Rockies...=20
Days 1-3... Maximum impact level from WSSI: Moderate to Major

Deep low pressure off CA will continue to infuse moisture across=20
the West with a separate trough pushing down the BC coast Friday=20
and over the northern Rockies Saturday providing a final focus for=20 precipitation and ending the active pattern.=20

Moderate to locally heavy snow for the length of the Cascades will
occur through today into early Saturday morning with snow levels=20
dropping on the WA Cascades from 3000ft to 1000ft and over the OR=20
Cascades to 2000ft. Snow probs for >8" are 50-90% on the WA/OR=20
Cascades including for the Snoqualmie and Santiam passes.

Moisture from the leading edge of the AR from the Pacific will
continue to maintain a prolonged moderate to heavy snow forecast=20
until the cold frontal passage later this evening. Snow levels=20
drop from 6000/7000ft to 3000/4000ft through this time leading to=20
increasing travel impacts. Snow probs for >8" are 50-90% over the=20
Sawtooths, northern ID/western MT ranges, western WY ranges, the=20
higher central NV ranges, and the Wasatch.

The progression of the cold front is notable with the Day 2 snow=20
probs for >8" limited to the Wasatch and 50-80% for northern and=20
western CO Ranges.

Jackson/Kleebauer


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5w3TbUg8Y9oJAqQvGcX7aMFVDpRF8TwGKKw-v-VfCNlHR= jP15638ILZXRJ6yNkbDkKwnNrS8Qi7kz_kEq-Rg3Pm5YCc$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!5w3TbUg8Y9oJAqQvGcX7aMFVDpRF8TwGKKw-v-VfCNlHR= jP15638ILZXRJ6yNkbDkKwnNrS8Qi7kz_kEq-Rg9_jxf4A$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 262108
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 PM EST Fri Dec 26 2025

Valid 00Z Sat Dec 27 2025 - 00Z Tue Dec 30 2025

*** Heavy Wintry Mix through tonight for the Northeast ***

*** Major Winter Storm Develops over the Great Lakes Sunday Night,
Spreading through the Northeast Monday ***

...Northeast...=20
Day 1... Maximum impact level from WSSI: Major=20

The variety of ptypes continue tonight for the central=20 Appalachians/Mid-Atlantic with heavy snow bands over eastern NY
through southern New England and the NYC metro. The main note is
the northward shift in the heavy snow a bit north of the NYC metro
that had been in the axis the past. Day 1 snow probs for >8" are
30-50% in the lower Hudson Valley, over western CT, and eastern
Long Island and around 10% in NYC proper. The stubborn cold air
damming will keep freezing rain continuing over the Laurel
Highlands and western MD until precip diminishes overnight.=20


...The West...=20
Days 1-2... Maximum impact level from WSSI: Moderate=20

Potent northern stream trough axis over Vancouver Island this
afternoon will continue to dig south as it tracks east over the
northern Rockies through Saturday night before shifting over the
northern Plains Sunday. Meanwhile the positively-tilted southern=20
stream trough along the northern CA Coast will swing east and cross
the central Rockies Saturday night. Long wave ridging behind this
trough finally brings an end to this active winter pattern.=20

Moderate snow continues for the Cascades and Sierra Nevada tonight.=20
Snow levels drop on the WA Cascades to 1000ft by early evening and
probably 500ft overnight, to 2000ft over the OR Cascades, and
around 4000ft on the Sierra. Day 1 Snow probs for >6" are 50-90%=20
on the WA/OR Cascades including for the Snoqualmie and Santiam=20
passes, and 40-60% for the Sierra Nevada.

Moisture streaming over the Intermountain West ahead of the trough
axis will continue to produce widespread snow over terrain through
Saturday. Day 1 snow probs for >6" are 60-90% over the northeast OR
and ID/western MT ranges where snow levels will drop to 2000ft
tonight and to ground level Saturday before snow tapers off. Those

6" probs are 40-80% for western WY ranges down through UT and

western CO where snow levels drop from 6000-8000ft now to
4000-7000ft overnight and 2000-6000ft Saturday.=20

On Saturday night the cold front associated with the strong trough
will quickly drop through the central High Plains and produce
moderate to heavy snow across the CO Rockies and some banded snow
for the Denver metro and east. Day 2 snow probs for >6" are over
50% for most of the CO ranges, with 30-60% probs for >2" broadly
along and east of the Palmer Divide.


...Great Lakes/Northeast...
Days 2-3... Maximum impact level from WSSI: Major

The potent northern stream trough reaching the northern Plains
Sunday will close off as it digs over Iowa through the day with the
surface low undergoing rapid intensification as it shifts northeast
over Michigan Sunday night into Monday. A rapid CAA pattern within
the northwest side of the cyclone will lead to comma head snowfall
Sunday afternoon over MN/western WI which quickly becomes lake=20
enhanced over northern WI/all of the U.P. Sunday night. Intense
flow behind the very deep system will produce strong lake effect=20
snow in its wake Monday.=20

Day 2.5 snow probs for >12" are 30-60% along the northern U.P.
and WI shorelines with most of that falling in just 12 hours. Those
probs for >12" increase to 50-80% and spread to far northern L.P.
for Day 3 once there's 24 hours worth of the event. Strong wind
will certainly make this event more significant.=20

Warm air advection ahead of this low will result in a wintry mix
over the Northeast with Day 3 0.1" ice probs 40-80% in north-
central PA through southern/eastern NY and central New England.

Key Messages have been initiated for this system.


Jackson



...Winter Storm Key Messages are in effect for the Great Lakes and
the Northeast as linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!8iGycxItJwAT0tIRVCrVSluWRyYd9CAQJjq7Y7Pwue0Yw= CKgq_E7UciAIWIwfjsvdiX4ZFHRBj1cVRx1BzK0jI3P0ac$=20

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!8iGycxItJwAT0tIRVCrVSluWRyYd9CAQJjq7Y7Pwue0Yw= CKgq_E7UciAIWIwfjsvdiX4ZFHRBj1cVRx1BzK0LZzA8_U$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 270723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 AM EST Sat Dec 27 2025

Valid 12Z Sat Dec 27 2025 - 12Z Tue Dec 30 2025

*** Major Winter Storm for the Upper Midwest/Great Lakes Sunday=20
Night then into the Northeast Monday ***

...The West...=20
Day 1... Maximum impact level from WSSI: Moderate=20

A healthy shortwave over the MT Divide this morning will continue=20
to move east-southeastward as a southern stream positively-tilted=20
trough (last gasp of the long-lived Atmospheric River event) moves=20
through the Great Basin into the Four Corners region. Moisture=20
anomalies are highest (>80th percentile) over the CO Rockies into=20
the Sangre de Cristos and snowfall amounts will be highest there,=20
generally above 9000-10,000ft.

On Saturday night the cold front associated with the strong trough
will quickly drop through the central High Plains and produce some
light/banded snow for the Denver metro region into the High=20
Plains. WPC probabilities for at least 8 inches of snow are highest

50%) above 8000ft or so. Lighter snow will affect the I-25=20

corridor from Fort Collins to Colorado Springs, but probabilities=20
for at least 2 inches of snow are generally less than 30%.


...Southeastern New Mexico...
Day 3... Maximum impact level from WSSI: Minor

Cold front racing southward from the CO Rockies will leave behind=20
a sfc-700mb baroclinic zone along the Rio Grande as moisture from=20
the Pacific will still be directed eastward across northern Mexico. Temperatures may be just cold enough even to the valley floors for
snow to accumulate, aided by an onset time overnight. WPC=20
probabilities for at least 2 inches of snow are >10% over most of=20 southeastern NM and across the TX border, and are >50% in the=20
Sacramento Mountains above 5000ft.=20


...Great Lakes/Northeast...
Days 2-3... Maximum impact level from WSSI: Major

The potent northern stream trough exiting Montana will close off=20
as it moves across the northern Plains then digs through Iowa late=20
Sunday. Upper jet will become more amplified overnight and help aid cyclogenesis across northern IL into Lower MI as pressures rapidly
drop through the 990s into the 980s mb after 00Z Monday. Snow=20
associated with the approaching cold front from the west will merge
into the developing comma-head snowfall to the northwest of the=20
sfc low Sunday afternoon along an inverted surface trough and on=20
the edge of the moisture gradient to the southeast (where PW=20
anomalies in the warm sector rise to >99th percentile). Snow will=20
expand and increase in intensity over eastern MN through=20
central/northern WI into the U.P. of Michigan as winds increase=20
from the NW to NE, picking up additional moisture from Lake=20
Superior. The low pressure will continue to deepen as it briefly=20
slows over northern Lower MI very early Monday awaiting the mid-
level low from the west. Shortly thereafter, it should reach peak=20
intensity (mid 970s mb) over Lake Huron or Georgian Bay with=20
continued wrap-around moisture as the WCB wraps up and around the=20
low. Snowfall will maximize over the northern short of the U.P.=20
where WPC probabilities of at least 12 inches of snow are >70%. As=20
the low continues through Ontario to Quebec, CAA will bring lake=20
effect snow to the rest of the Great Lakes into D3. WPC=20
probabilities for at least 6 inches of snow D3 are highest south of
Buffalo in the Chautauqua Ridge, aided by a multi-lake connection.
The bombing out of the system will induce strong winds over much=20
of the region, creating additional hazards due to blowing/drifting=20
snow.

Well ahead of the main surface low, warm air advection will=20
overrun cold <32F surface temperatures in the central Appalachians=20
into the Northeast. With precipitation starting overnight, and snow
on the ground through much of the region already, the WAA aloft=20
will have a tough time reaching the surface. This could result in a
widespread icing event to start for central PA northward into the=20 Adirondacks/eastern NY and much of New England. Without a surface=20
high to the north, temperatures will have an easier time rising due
to the freezing rain process itself, but counteracted by snow-=20
covered ground which could act to keep the surface warm front=20
farther south. It may only be when the cold front (or triple point=20
low) approaches that the surface inversion mixes above freezing,=20
albeit briefly. This may be especially true over central/northern=20
New England as the guidance indicates a triple point low could form
and act to keep northern areas below freezing at the surface. WPC=20 probabilities for at least 0.10" icing are >50% over parts of north
central PA and from the Catskills northward into the Adirondacks=20
and eastward through central New England (along/north of the Mass=20
Pike/495) and into western Maine. Greater than 50% probabilities=20
for at least 0.25" icing exist over the Adirondacks and into=20
central VT/NH. Over far northern Maine, though some icing may creep
that far north, snow will be the dominant ptype and WPC=20
probabilities for at least 4 inches of snow are >50% over the North
Woods.


Fracasso


...Winter Storm Key Messages are in effect. Please see current Key
Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!80PYub2ZplDosmeyJ8tIzedJLPmNrNjDbJu4BrjFSG2B9= NJmNb0Hphsqi7fTPlk7IEZ7VeTsrztbptx_IacGPWZVvCQ$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 272054
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 PM EST Sat Dec 27 2025

Valid 00Z Sun Dec 28 2025 - 00Z Wed Dec 31 2025

*** Major Winter Storm for the Upper Midwest/Great Lakes Sunday=20
Night then into the Northeast Monday ***

...Southern Rockies onto the High Plains...=20
Day 1... Maximum impact level from WSSI: Moderate

Northern stream shortwave trough axis over central MT will close
into a low over ND tonight as a reinforcing shortwave dives
southeast over WY. Remnant Pacific moisture will continue to
maintain moderate snow rates over the CO and northern NM Rockies
tonight with snow levels decreasing to valley floors before snow
tapers off early Sunday. Day 1 PWPF for >6" additional after 00Z=20
are 50-70% for northern and western CO Rockies.


The cold front associated with the strong trough will quickly drop
through the central High Plains tonight where left exit dynamics
from a SWly jet ahead of the trough will aid snow and development=20
for the Denver metro region east into Nebraska late tonight into
Sunday. Day 1 PWPF for >2" are 30-50% for the Palmer Divide and
generally less than 10% for the High Plains, though this phenomena
is rarely picked up well by models.=20


...Southeast New Mexico/Guadalupe Mountains...=20
Days 2/3... Maximum impact level from WSSI: Moderate

Cold front racing southward from the CO Rockies Sunday will leave=20
behind a sfc-700mb baroclinic zone along the Rio Grande as moisture
from the Pacific will still be directed eastward across northern=20
Mexico. Temperatures may be just cold enough even to the valley=20
floors for snow to accumulate, aided by an onset time early Monday
with the threat continuing through Monday night. Topographic
enhancement on the Guadalupe and southern Sacramento Mtns raises
Day 2 PQPF for >4" into the 20-40% range in this terrain.


...Great Lakes/Northeast...
Days 2-3... Maximum impact level from WSSI: Major

The potent northern stream trough exiting Montana this evening=20
will close off over ND tonight and jog southeast to Iowa Sunday as
southern stream elements phase in. This will promote rapid surface=20 cyclogenesis as it tracks from northern IL Sunday afternoon through
Lower MI Sunday night.=20

Snow associated with the approaching cold front from the west will
merge into the developing comma-head snowfall to the northwest of=20
the sfc low over MN/northern WI Sunday afternoon along an inverted
surface trough and on the edge of the moisture gradient to the=20
southeast (where PW anomalies in the warm sector rise to >99th=20
percentile). Snow will expand and increase in intensity over=20
northern WI/U.P. of MI Sunday evening, quickly becoming enhanced by
Lake Superior as cyclonic flow rapidly intensifies. Meanwhile,
east/ahead of the low center will be a wintry mix over the northern
L.P. and eastern U.P. with sleet and freezing rain eventually
giving over to snow early Monday.

The low pressure will continue to deepen as it briefly slows over=20
Lake Huron early Monday as the system becomes vertically stacked=20
and occludes. awaiting the mid- level low from the west. Peak
intensity is then Monday morning with MSLP in the mid 970s over=20
Lake Huron or Georgian Bay with the warm conveyor belt now
completed wrapped up and around the low. Snowfall will maximize=20
over the northern shore of the U.P. where powerful onshore flow=20
pivots as the low passes with 1-2ft likely. Day 1.5 PWPF for >6"=20
are over 20% from northern Iowa across eastern MN and central WI,=20
expanding across the northern and western L.P. for Day 2.

Strong westerlies then scream east Monday promoting turbulent LES
banding off Lake Michigan with single banding threats off Lakes=20
Erie and Ontario coupled with blowing/drifting snow. Day 3 PWPF=20
for >8" are over 50% above Erie, PA through the Chautauqua Ridge=20
and south towns of Buffalo as well as across Syracuse and up=20
through the Tug Hill Plateau.=20

Well ahead of the main surface low, warm air advection will=20
overrun cold <32F surface temperatures from central PA Sunday
afternoon through the Northeast Sunday night. Given snow is on the
ground through much of the region, the WAA aloft will have a tough
time reaching the surface. Day 1.5 PWPF for >0.1" is 40-60% in
central PA across the Catskills and southern New England with Day 2
PWPF for >0.25" 50-70% for the northern Hudson Valley through the
Adirondacks and along the St Lawrence, and across VT/NH into
Maine. It is worth noting that without a surface high to the=20
north, temperatures will have an easier time rising due to the=20
freezing rain process itself, but again counteracted by snow-=20
covered ground which could act to keep the surface warm front=20
farther south. It may only be when the cold front (or triple point=20
low) approaches that the surface inversion mixes above freezing,=20
albeit briefly. This may be especially true over central/northern=20
New England as the guidance indicates a triple point low could form
and act to keep northern areas below freezing at the surface.=20
A snow line looks to set up over far northern NH and northwestern
Maine where Day 3 PWPF for >4" are 40-60%.


Jackson



...Winter Storm Key Messages are in effect for the Great Lakes and
Northeast and linked below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!-DKELbdACovotXfhPRFe2xuGWS9RPcu6ogCKXoshfphFi= ETLGYltZgapEL0F8gRS-iECCckrboM33Ho2Tm9UNagCyeI$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)

FOUS11 KWBC 280724
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 AM EST Sun Dec 28 2025

Valid 12Z Sun Dec 28 2025 - 12Z Wed Dec 31 2025

*** Major Winter Storm for the Upper Midwest/Great Lakes tonight=20
then into the Northeast Monday ***


...Southeast New Mexico/Guadalupe Mountains...=20
Day 2... Maximum impact level from WSSI: Moderate

A cold front racing southward from the CO Rockies today will leave
behind a sfc-700mb baroclinic zone along the Rio Grande as=20
moisture from the Pacific will be directed eastward across northern
Mexico. Temperatures may be just cold enough even to the valley=20
floors for snow to accumulate, aided by an onset time early Monday=20
D2 with precipitation continuing through Monday night. Topographic=20 enhancement on the Guadalupe and southern Sacramento Mountains will
result in the highest probabilities for at least 4 inches of snow=20
-- generally 40-60%. To the east, light snow of a couple inches is=20
possible to the TX border where WPC probabilities of at least 2=20
inches are 20-50%.


...Great Lakes/Northeast...
Days 1-3... Maximum impact level from WSSI: Major to locally=20
Extreme

A vigorous closed low along the Montana/North Dakota border this=20
morning will dig southeastward into Iowa this evening as the upper=20
jet punches northeastward into the western Great Lakes. This will=20
set the stage for a rapidly-deepening/bombing cyclone the will move
across Lower Michigan tonight then into Canada on Monday. The=20
storm will have three main facets: synoptic snow via comma-=20 head/lake-enhancement from MN to the U.P. of Michigan, freezing=20
rain to its east (PA/Northeast US) in advance of a surface warm=20
front, and lake- effect snow as the system departs across all Great
Lakes.

Snow associated with the approaching cold front from the west will
merge into the developing comma-head snowfall to the northwest of=20
the sfc low over MN/northern WI this afternoon along an inverted=20
surface trough and on the edge of the moisture gradient to the=20
southeast (where PW anomalies in the warm sector rise to >99th=20
percentile). Snow will expand and increase in intensity over=20
northern WI/U.P. of MI this evening, quickly becoming enhanced by=20
Lake Superior as cyclonic flow rapidly intensifies. Just east/ahead
of the low center will be a wintry mix over the northern L.P. and=20
eastern U.P. of Michigan with sleet and freezing rain eventually=20
giving over to snow early Monday.

The low pressure will continue to deepen and briefly slow over=20
Lake Huron early Monday as the system becomes vertically stacked=20
and occludes (awaiting the mid-level low from the west). Peak=20
intensity should be reached Monday morning (mid 970s mb central=20
pressure) over Lake Huron or Georgian Bay with the warm conveyor=20
belt now completed wrapped up and around the low. Snowfall will=20
maximize over the northern shore of the U.P. where powerful onshore
flow pivots as the low passes. Locally, 1-2ft of snow is likely=20
over much of the U.P. D1-2 probabilities of at least 6 inches of=20
snow are >50% from south central MN eastward across the northern=20
1/2 of WI and the northern 1/4 of Lower Michigan northward across=20
all of the U.P., where probabilities of at least 12 inches are=20

70%. Probabilities for at least 24 inches of snow are >20% over=20

much of the northern and eastern U.P.=20

Well ahead of the main surface low, warm air advection will=20
overrun cold <32F surface temperatures from central PA this=20
afternoon through the Northeast tonight. Given snow is on the=20
ground through much of the region, the WAA aloft will have a tough=20
time reaching the surface, especially in normally sheltered=20
locations. Without a surface high to the north, temperatures will=20
have an easier time rising due to the freezing rain process itself,
but again counteracted by snow-covered ground which could act to=20
keep the surface warm front farther south. However, with such a=20
strong southerly flood of warm air, most guidance does show at=20
least a brief changeover to rain for nearly all of the Northeast=20
except for northern New England. Where the cold air holds on the=20
longest, ice could accumulate enough to be hazardous to trees=20
and/or power lines. WPC probabilities for at least 0.25" icing are=20

50% over the Adirondacks and across much of central VT/NH into=20

southwestern Maine. In addition, probabilities for at least 0.50"=20
icing are 20-50% in these regions. Across northern Maine, the=20
column may be stay entirely below freezing near the Canadian border
as a triple point low may help prevent a southerly wind component.
WPC probabilities for at least 4 inches of snow are >30% over far=20
northern Maine.=20

As the low moves through Ontario into Quebec, strong westerlies=20
will favor lake-effect snow across all Great Lakes, but focused=20
downwind of Lakes Michigan, Erie, and Ontario. Some multi-lake=20
connection and variable wind directions could support long-lived=20
single bands far inland away from the lake shores in concert with=20 breezy/windy conditions (i.e., blowing and drifting snow). In=20
addition, upslope flow into the central Appalachians will favor=20
some snow into the Laurel Highlands southward to eastern WV. WPC=20 probabilities for at least 8 inches of snow are >50% over northeast
Ohio and NW PA into the Chautauqua Ridge and south towns of=20
Buffalo as well as over central NYS around Syracuse northward to=20
Watertown and the Tug Hill Plateau. Some areas could see more than=20
12 inches of snow where bands maintain some residence time (>50%=20
chance).=20


Fracasso/Jackson


...Winter Storm Key Messages are in effect. Please see current=20
Key Messages below...

https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!5e4mWU_BbGp6NVxpLE-fbj3sgOfKqTOUhHgdpw2OEItZd= d9WYVDF8OU5YYt0X2VOgRWMrOplBP1Qn3Te_cD8HaImg7I$=20



$$

=3D =3D =3D
To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM.

--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (1:2320/105)