FOUS30 KWBC 300800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Tue Dec 30 2025

Day 1
Valid 12Z Tue Dec 30 2025 - 12Z Wed Dec 31 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Wed Dec 31 2025 - 12Z Thu Jan 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

A large upper level Pacific low will track east and approach the
coast of Southern California on New Year's Eve. The low will
gradually weaken with time, and remain under a ridge in the
polar jet, thus keeping the low cut off from the main jet stream.
The low will draw an unusually moist, tropical air mass northward
up the Mexican coast and into Southern California. The predominant
850 flow will be out of the southeast for much of the day
Wednesday, but will turn more out of the south-southwest by New
Year's Night. This pattern will keep rainfall into the Transverse
Ranges, and much of southern California for that matter, rather
light through the day. However, once the flow turns to become more
orthogonal to the coast Wednesday night, rainfall rates will
increase into the Transverse Ranges. The orthogonal turn of the
flow will correlate with the closest approach of both the upper
level trough and corresponding surface low. These will also enhance
rainfall rates into the mountains.

Hydrologically, while Southern California has had some time to
recover from the Christmas rainfall event, it's still too soon
after the event for full drainage to have occurred. Forecast
rainfall has increased in the past 24 hours, due in part to a
closer approach of the surface low to the coast relative to the
forecast last night. As such, a higher end Slight was issued for
much of the Transverse Ranges, where 2-4 inches of rain are
forecast through the period. Much of that rain will fall between
06Z and 12Z Thursday morning. Meanwhile, in the adjacent L.A.
Basin, 1-2 inches of rain are expected. Between burn scars and
urban concerns, this amount of rain should lead to scattered
instances of flash flooding. Thus, the Slight Risk inherited
remains in place. Further increases to the rainfall forecast may
require an additional upgrade to a Moderate Risk with future updates.

Wegman


Day 3
Valid 12Z Thu Jan 01 2026 - 12Z Fri Jan 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

A Slight Risk upgrade was introduced with this update, for many of
the same areas as the Day 2 Slight Risk. At the start of the period
New Year's morning, the brunt of the event will be well underway
across Southern California. Heavy rain will continue into the
morning hours as the surface low and upper level trough finally
move ashore during the day Thursday. Thus, the heaviest rains are
expected Thursday morning. Behind the low Thursday afternoon and
into the overnight, the rain should largely end for most, tapering
to a few showers here and there. Thus, this Slight Risk is really
for the first half of the day, and should be able to be dropped
after that. Nonetheless, an additional 1-2 inches of rain on top of
the rains from the overnight will continue to cause flooding
concerns across Southern California. So while amounts in total will
be less Thursday than on Wednesday, the continuation of Wednesday's
rain on into Thursday will keep the commensurate impacts ongoing as well.

Further north, a Marginal Risk remains in place for portions of the
northern California coastal ranges and extending south along the
Sierra Nevada foothills. The rain in these regions Thursday and
Thursday night will be much more evenly spread in time. However,
these areas are much more equipped to handle the expected rain,
especially since full recovery from the Christmas rainfall event
has already occurred. An isolated instance or two of flash flooding
can't be ruled out, hence the Marginal, but overall impacts into
central and northern California should be minimal.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 290806
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
306 AM EST Mon Dec 29 2025

Day 1
Valid 12Z Mon Dec 29 2025 - 12Z Tue Dec 30 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Tue Dec 30 2025 - 12Z Wed Dec 31 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Wed Dec 31 2025 - 12Z Thu Jan 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

A potent upper level shortwave trough will move east through the
day Wednesday and approach the southern California coast New Year's
night. As it approaches, the attendant surface low will tap into a
large plume of subtropical moisture that will advect north on the
southerly flow ahead of the trough. The trough itself will be
negatively tilted, supporting cyclogenesis. The surface low will
elongate thanks to the negatively tilted trough, allowing the
southerly flow to spread rainfall north along essentially the
entire California coast. However, with southerly flow, the east-
west oriented Transverse Ranges will be particularly well set up to
capture that moisture and wring it out in the form of upslope
rainfall, in much the same way as the Christmas rainfall event a week ago.

The difference between the Christmas and New Year's rainfall events
in California will be the depth of moisture (less of it this time
around), and lack of instability this time. This combined with the
first part of the event having a southeasterly flow in the lower
levels should help to mitigate the total rainfall impacting the
L.A. Basin and the Transverse Ranges relative to the Christmas rainfall
event. Forecasted PWATs will be around 1.25 inches near the coast.
This is still 4 sigma above normal for this time of year, and
therefore still represents a highly unusual amount of available
moisture. The latest forecast has up to an inch of rain
overspreading much of the lower elevations of the L.A. Basin, while
1-3 inches of rain are forecast for the south- facing slopes of
the Transverse Ranges. Full reservoirs from the Christmas event,
some draining still ongoing due to wetter than normal soils for
this time of year, burn scars, and urban effects should all work to
worsen any flooding effects from the expected rainfall. Thus,
while forecasted rainfall amounts are lower, expect that there will
still be widely scattered instances of flash flooding, especially
in and around burn scars.

A Slight Risk upgrade was introduced with this update, in
coordination with LOX/Oxnard, CA forecast office. Fortunately,
unlike the Christmas rainfall event, for the aforementioned
reasons, do not expect to have additional upgrades in this area.
Short of some much larger forecast change that results in much
higher forecasted rainfall amounts into SoCal, a possibility with a
low probability of occurring, this should be the final risk
category upgrade. Nonetheless the forecast should continue to be
monitored for the latest updates.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 270745
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Sat Dec 27 2025

Day 1
Valid 12Z Sat Dec 27 2025 - 12Z Sun Dec 28 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Sun Dec 28 2025 - 12Z Mon Dec 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NORTHERN
ILLINOIS THROUGH WESTERN NEW YORK...

A Marginal Risk upgrade was introduced with this morning's forecast
update across a portion of the Great Lakes, in coordination with a
couple of the impacted forecast offices. While the atmospheric
river event in California is long over, the remnant moisture
therefrom has continued east and will be harnessed by a developing
storm system across the Midwest. The low center will track from
near Kansas City Sunday morning to over Lake Huron by Monday
morning. In that time it will deepen from around 1000 mb Sunday
morning to around 974 mb Monday morning. This rapid cyclogenesis
will allow the moisture to the tune of 5 sigma above normal for
this time of year, as well as IVT values over 750 kg/m/s will
support additional dynamic lift along the warm front which extends
east of the low, and along its cold front to the low center's south.

Elevated convection resulting in locally heavy rainfall is
likely, despite the fast movement of any convective cells. Bare
ground is in place across most of the Marginal Risk area. Due to
lack of flora, it should take longer for the rainfall to penetrate
into the ground, resulting in more runoff. Urban areas in the rain
shield, including Chicago, Detroit, and Buffalo could see urban and
small stream flooding. Across upstate New York, at the higher
elevations some snowpack remains, especially east of the lower
lakes. This too could locally contribute to rising stream and creek
levels leading to isolated instances of flash flooding.

Wegman


Day 3
Valid 12Z Mon Dec 29 2025 - 12Z Tue Dec 30 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 281008
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
508 AM EST Sun Dec 28 2025

Day 1
Valid 12Z Sun Dec 28 2025 - 12Z Mon Dec 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN NEW YORK...

...New York...

The warm front associated with a rapidly deepening low that will
track from the central Plains to the northern mitten of Michigan
today will move into western New York later this morning. This warm
front will advect much warmer air behind it, to its south, which in
turn will change over any wintry precipitation ahead of it to
plain rain. Dynamics associated with the rapidly deepening low,
including well above normal amounts of atmospheric moisture, some
instability, and slow northward movement, will all allow rain,
heavy at times, to persist from when it starts later this morning
through into tonight, when the trailing cold front sweeps across
western New York, ending any warm precipitation, as much colder
Canadian air rushes in behind the cold front. This extended period
of warm rainfall will occur over a below-normal, but still fairly
robust snow pack at the higher elevations of the Southern Tier, to
the amount of 1-4 inches of snow water equivalent. Thus, the
combination of rain and snow melt should rapidly increase stream,
creek, and river levels across western New York. Thus, the flooding
threat has increased and a Slight Risk for portions of western New
York, generally west of Rochester and north of the PA State Line,
remains in place. Urban and small stream flooding look to be the
types of flooding that are most likely, but any flood-prone area
will be susceptible today and especially into tonight.

...Midwest...

A Marginal Risk extends from northern Illinois across much of
southern Michigan. The warm front with embedded elevated convection
will persist through the entire day in the Marginal Risk area. The
cold front will swing west to east from late this afternoon in
Illinois to this evening across Michigan. This will effectively end
the flooding threat as much colder air turns any lingering
precipitation tonight over to snow, and the lakes help with
localized enhancement across western lower Michigan. Urban and
small stream flooding are possible in the Chicago area, Detroit,
and any smaller urbanized areas in between. Due to relatively dry
conditions across the Midwest prior to today, any instances of
flooding should be isolated.

The rain has already started out this early morning to the
southwest of the Marginal Risk area across portions of Missouri,
Iowa, and western Illinois. For these areas, even drier soils prior
to this storm should keep the flooding threat below the 5% Marginal
Risk threshold, but the area will be monitored for overperformance
and any potential need to extend the Marginal Risk south and west
for the morning into these areas.

Wegman


Day 2
Valid 12Z Mon Dec 29 2025 - 12Z Tue Dec 30 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Tue Dec 30 2025 - 12Z Wed Dec 31 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 261601
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1101 AM EST Fri Dec 26 2025

Day 1
Valid 16Z Fri Dec 26 2025 - 12Z Sat Dec 27 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

1600Z Update...

The Marginal Risk area has been expanded north to include much of
northern CA, including the coastal ranges, Bay Area, and northern
portions of the Central Valley. The arrival of a fairly strong
500/700 mb low center just offshore will be driving areas of heavy
showers going through the afternoon hours. While this energy will
be generally weakening with time, the addition of at least modest
boundary layer heating along with some steepening of the mid-level
lapse rates should favor some convective elements capable of
producing localized rainfall rates of 0.50" to 0.75"/hour. Some
localized additional rainfall totals of 1 to 2 inches will be
possible, and especially across the northwest CA coastal range.
These additional rains may foster some additional localized runoff
concerns given the wet/saturated soil conditions and elevated
streamflows. No changes have been made to the Slight Risk area
farther south across southern CA as the threat of heavy rain will
continue here into at least the early evening hours.

Orrison

Previous discussion...

Few changes were needed for this morning's update. A positively-
tilted upper level trough will push ashore and inland across the
Pacific Northwest today. This will keep the flow at all levels
unidirectional out of the southwest across Southern California, on
the leading edge of a 140 kt jet. As the trough pushes east, less
and less of it will be over the Pacific, resulting in a diminishing
of the onshore flow with time. Waves of rainfall will push ashore
into southern California through the day. Lingering instability
will support rates that may be heavy at times. This is most likely
as the storms interact with the terrain of the eastern Transverse
Ranges, from L.A. north and east. It is in this area that the
rainfall forecast peaks at around 3 inches at the highest
elevations. Meanwhile most of the L.A. Basin picks up another 1-2
inches. 1-2 inches of rain would be problematic on a normal day,
but following multiple days of multiple inches of rain per day,
making the 1-2 inches expected today lighter by comparison...expect
scattered instances of flash flooding to redevelop again today.
While all areas of coastal Southern California and the Los Angeles
basin will pick up some rain, those highest totals will be north
and east of the downtown area. Thus, from downtown L.A. north and
east, a higher end Slight is in effect. The flooding impacts will
be the result of continued drainage of prior rainfall over
Christmas Eve and Day, as well as urban effects. A Moderate Risk
may need to be considered from Pasadena east through San Bernardino
if rainfall amounts exceed expected totals.

Elsewhere, the Slight remains in place down the coast to about San
Diego, as the eastward moving bands of rain impacting the L.A.
Basin should struggle to continue further south. Meanwhile the
Marginal for limited shower activity and/or lowering snow levels in
the foothills of the Sierra Nevada remains in place unchanged with
this update. For Central and Northern California, it's probable
that there will be more total precipitation in these parts of the
state compared to further south, but because of lowering snow
levels due to cold air influx with the aforementioned trough
moving in, much of it should fall as snow at the higher elevations,
reducing the flooding threat downstream.

By this evening, the flow will flip around to the northwest,
ushering in drier air and finally ending the rainfall threat across
Southern California likely for the rest of 2025.

Wegman


Day 2
Valid 12Z Sat Dec 27 2025 - 12Z Sun Dec 28 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

Day 3
Valid 12Z Sun Dec 28 2025 - 12Z Mon Dec 29 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

An area of rainfall across much of the Midwest is expected with a
developing low moving into the Great Lakes. The combination of
prior dry soil conditions, rapid movement, poor instability, and
cold air following the rain should all work to keep this event
largely beneficial. There are no flooding concerns in this area at
this time due to these factors.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 190829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 AM EST Fri Dec 19 2025

Day 1
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

...Pacific Northwest...

Ongoing atmospheric river will drift southward while swift flow
aloft transports the plume of deep layer moisture into parts of
the northern Great Basin. IVT values at or above 700 units are
forecast to cover much of Oregon initially before it weakens as
the axis of the moisture plume and associated precipitation settles
into northern California. The Marginal Risk was maintained for
southwest Oregon and northern California, as well as the Slight
Risk over northwest California. Minimal adjustments were made to
account for the latest QPF trends and WPC forecast.

...Southern New England...

Locally heavy rainfall will be possible for portions of the
Northeast during this period as moisture drawn northward encounters
the advancing trough over the eastern states. With time the
the moist flow aloft becomes increasingly diffluent and a surface
warm front approaches from the south early on Friday. WPC
Deterministic QPF in the 1.0 to 1.4 inch range is forecast along
the track of the low. Offsetting the potential of excessive
rainfall by limiting rainfall rates/amount is the meager
instability expected to be in place. A Marginal Risk was maintained
from the New York/Connecticut/Massachusetts border to downeast Maine.

Campbell/Bann


Day 2
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

A relative lull in moisture surges expected during the majority of
this period before the next stronger atmospheric river from the
Pacific reaches northern California towards the end of Day 2.
Although there may be some overlap in heavy rainfall, the axis of
the strongest on-shore winds and the greatest on-shore moisture
transport looks to be south of the axis of the previous event.

Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south of
the Oregon/California border by early Saturday evening. Given such
high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). The urban centers
between Sacramento to San Francisco will be more at play this period lead

Campbell/Bann


Day 3
Valid 12Z Sun Dec 21 2025 - 12Z Mon Dec 22 2025

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL IN EFFECT FOR
NORTHERN CALIFORNIA...

The Atmospheric River will strengthen over the northern half of
California resulting in scattered to widespread areas of enhanced
rainfall overlapping much of the same footprint from the Day 2
period. The latest guidance is suggesting daily accumulations of 3
to 7 inches, with 48 hour totals nearing 5 to 9 inches. A Slight
Risk is in effect from the West Coast to much of the Sierra Nevada
Range. There may be a need for an upgrade for portions of the
Sierra Nevada should guidance continue to increase over this area.

Campbell
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 180832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Thu Dec 18 2025

Day 1
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
WESTERN OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND THE
NORTHWEST CORNER OF CALIFORNIA...

A well define plume of deep moisture will continue to approach the
coast and then progress inland bringing widespread coverage of
moderate or greater rainfall to portions of western Oregon and a
small part of adjacent Washington and the northwest corner of
California. After several runs where the guidance has shown a
subtle northward shift of the moisture plume and associated
rainfall...there was subtle shift southward in the latest suite of
guidance necessitating a small shift in the north/south position of
the Slight Risk along/near the Oregon Cascades. Overall...the risk
within the Slight Risk area remained along the west aspect of the
Cascades where the moisture plume encounters the Cascades and is
forced to lift orographically. Guidance showed widespread 3 inch to
6 inch precipitation amounts within 24hrs with isolated higher
totals depicted by the convective allowing models in and near the
terrain. Both the HREF and RRFS continued to show high
probabilities of 0.50"+/hr rainfall rates especially after 21Z
today which persists through 12Z Friday. Therefore, the potential
for small stream and/or river flooding continues to increase with
this event (per collaboration with the National Water Center).
However the potential for flash flooding (more short- fused
inundation), especially over burn scars, is also increasing.

Bann


Day 2
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

...Pacific Northwest...

The atmospheric river that came on-shore in the Day 1 period will
be on-going across Oregon...although the event should be winding
down in terms of rainfall rates and additional amounts fairly early
in the outlook period. A well-defined plume of deep layer moisture
will continue to be drawn from the eastern North Pacific Ocean
eastward into parts of the northern Great Basin by fast westerly
flow aloft. IVT values at or above 700 units are forecast to cover
much of Oregon initially...then weaken as the axis of the moisture
plume and associated precipitation settles into northern
California. Maintained a large amount of continuity in terms of
placement of the Slight Risk area clipping northwest California and
a portion of adjacent southwest Oregon.

Saw little reason to make any significant changes to the expanded
coverage of the Slight Risk area made yesterday to cover more into
the Trinity Mountains given latest QPF.

...Southern New England...
A trough crossing the eastern United States will draw increasing
amounts of moisture northward into parts of New England...helping
set the stage for locally heavy rainfall when flow aloft becomes
increasingly difluent and a surface warm front approaches from the
south early on Friday. WPC Deterministic QPF in the 1.0 to 1.4 inch
range is forecast along the track of the low. Offsetting the
potential of excessive rainfall by limiting rainfall rates/amount is
the meager instability expected to be in place.

Bann


Day 3
Valid 12Z Sat Dec 20 2025 - 12Z Sun Dec 21 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN PORTIONS OF
NORTHERN CALIFORNIA|...

Renewed rainfall is expected across northern California as yet
another push of moisture arrives on the heels of the AR which
departed during the day on Friday, The axis of the strongest on-
shore winds and the greatest on-shore moisture transport looks to
be south of the axis of the previous event, but there is likely to
be at least some overlap between the two rainfall footprints.
Precipitable water values increase to between 1.2 and 1.4 inches
along the northern California coast north of San Francisco south
of the Oregon/California border by early Saturday evening. Given
such high snow levels...there is not a lot of concern about
precipitation type until the moisture laden flow reaches the
northern end of the Sierra Nevada range (save for a few mountain
tops along the trajectory inland from the coast). With the areal
average amount of the rainfall forecast being in the 1 to 2 inch
range...will keep the Marginal Risk inherited from yesterdays Day
4 ERO and plan to adjust as needed when placement and amounts
become more locked in,

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 170823
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Wed Dec 17 2025

Day 1
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 2
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER WESTERN
OREGON EXTENDING INTO A SMALL PORTION OF WASHINGTON AND
CALIFORNIA...

The next in a series of atmospheric rivers will arrive along the
west coast of North America early on Thursday. The threat for
significant rainfall remains elevated across the western half of
Oregon with a focal point for maximum precipitation centered over
the southern Cascades and the adjacent valleys on either
side...although a subtle northward shift was noted in the 17/00Z
guidance. The key in this threat is the projected "spillover" of
heavier precip to the leeward side of the Cascades due to a
pronounced 700mb jet from the Pacific leading to significant
Pacific moisture being drawn inland. This is the area where ARI
forecasts are hovering between the 25-100 year exceedance
intervals, matching the output from the past several model runs and deterministic QPF from WPC. As a result, Day 2 excessive rainfall
outlook was expanded the Slight Risk northward across portions of
the Washington Cascades in response to the subtle northward shift
noted earlier...with little reason to expand any farther eastward.

Bann


Day 3
Valid 12Z Fri Dec 19 2025 - 12Z Sat Dec 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL MAINLY OVER
PORTIONS OF NORTHWEST CALIFORNIA...

The atmospheric river that came on-shore on Thursday will be on-
going across much of Oregon as the Day 3 period begins at 12Z on
Friday. A well-defined plume of deep layer moisture will continue
to be drawn from the eastern North Pacific Ocean eastward into
parts of the northern Great Basin by fast westerly flow aloft. IVT
values at or above 600 units is forecast to cover much of Oregon initially...then weaken as the axis of the moisture plume and
associated precipitation settles into northern California. The
system looks to have trended a bit more progressive on Friday than
suggested by earlier runs...so some of the QPF values over Oregon
and northwest California have come down a bit. Even so...opted to
maintain a large amount of continuity with Slight Risk area over
northwest California and a portion of adjacent southwest Oregon
given the possibility of further wobbles in the placement of the
axis or variations in model QPF. As it stands...the area average
precipitation amounts are currently in the range of 1-2 inches
with localized higher amounts maxima in the terrain.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 250802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
302 AM EST Tue Nov 25 2025

Day 1
Valid 12Z Tue Nov 25 2025 - 12Z Wed Nov 26 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST AND SOUTHERN APPALACHIANS, AND ALSO FOR THE COASTAL
PACIFIC NORTHWEST...

...Southeast states...

The storm system crossing the southern tier states will continue
to have a plume of Gulf moisture surging north ahead of the cold
front through Tuesday afternoon, mainly from southeastern
Mississippi to the southern Appalachians. The magnitude of the
rainfall and also the coverage is expected to wane compared to
yesterday as the storm system becomes more elongated and
progressive. Recent CAM guidance has swaths of QPF maxima on the
order of 1.5 to 3 inches from central Alabama to eastern Tennessee
and western North Carolina, with the RRFS taking some of the
heavier rains as far north as the Kentucky state line. Only small
changes were necessary to the inherited Marginal Risk area, with a
modest extension northward to include more of the southern
Appalachians, and a little farther westward to areas closer to the
Mississippi border.

...Pacific Northwest...

A marginal atmospheric river event will affect the coastal ranges
and the Cascades from central Oregon northward through Tuesday
night, followed by lighter precipitation going into Wednesday.
There will not be much instability to work with, so this will tend
to keep rainfall rates in check, but the duration of moderate
rainfall with rates near 0.25 inches per hour leading to areas of
1-2 inch daily rainfall totals may just be enough to lead to some
localized instances of minor flooding from the northern coastal
ranges of Oregon to the Olympic Peninsula. The timing for this has
also sped up some, to the point where the majority of the rainfall
is now expected in the Day 1 period instead of the Day 2 period,
so no areas are necessary at this time beyond 12Z Wednesday for
this region.

Hamrick


Day 2
Valid 12Z Wed Nov 26 2025 - 12Z Thu Nov 27 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hamrick


Day 3
Valid 12Z Thu Nov 27 2025 - 12Z Fri Nov 28 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hamrick
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 300800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sun Nov 30 2025

Day 1
Valid 12Z Sun Nov 30 2025 - 12Z Mon Dec 01 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND DEEP SOUTH...

A fast-moving positively tilted shortwave trough will move east in
parallel with a strong cold front that will sweep across the South,
drawing abundant Gulf moisture for December north and east along
the frontal interface. The enhanced lift associated with both the
shortwave trough and attendant jet streak will favor cyclogenesis,
especially Monday night as the low forms across far southern
Georgia and coastal South Carolina. While the cold front will push
the Gulf moisture with embedded thunderstorms along to the east, by
the time the low forms along the front, it will have generally
stalled out, with little southward progress. This should act to
keep the pattern quite progressive, even if areas will still see
heavy rain from thunderstorms. Further, the soil moisture levels
across much of the South are below to well below average. This
should support the soils largely soaking up the mostly stratiform
(albeit with embedded convection) rain. There were few changes made
to the Marginal Risk area, as the area of greatest concern for
isolated instances of flash flooding are the urban centers from
Houston east through New Orleans, Montgomery, and Atlanta.

Wegman


Day 3
Valid 12Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The inherited Marginal Risk along much of the Eastern Seaboard from
South Carolina north through Massachusetts was dropped, resulting
in another blank ERO map with this update. The progressive nature
of the low as it moves up the coast, despite somewhat rapid deepening,
has resulted in an eastward shift of the heaviest precipitation
more off the coast. For those areas not impacted by wintry weather
in the interior Northeast/Appalachians, the rainfall along the
coastal plain will be almost entirely stratiform, with any
convection confined perhaps to the eastern Carolinas. Even in the
Carolinas any convection will be fast-moving and embedded within a
much larger stratiform rain shield. Thus, the combination of lower
forecast rainfall amounts and the stratiform nature of the rain
should result in a rather long-duration light rain along the coast
in most areas. The heaviest rains Tuesday could even remain east of
the I-95 corridor, and thus largely missing the bigger metros. Just
like in the Deep South, soils along the Eastern Seaboard are also
drier to much drier than normal for this time of year. Thus, any
rainfall will be largely beneficial in these areas as well.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 010800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Mon Dec 1 2025

Day 1
Valid 12Z Mon Dec 01 2025 - 12Z Tue Dec 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND DEEP SOUTH...

Very few changes were needed to the Marginal Risk area that
stretches from the Upper Texas Coast north and east along the Gulf
coast and into central Alabama and Georgia. A progressive shortwave
trough will round the southern periphery of an expansive upper
level low centered north of Hudson Bay, well into Canada. The
shortwave trough and associated 120-150 kt upper level zonal jet
will provide the forcing to allow storms to strengthen as southerly
flow off the Gulf provides ample moisture for the storms. The
limiting factor for heavy rainfall will be a lack of
instability...and while values could reach into the 500-1,000 J/kg
range, this along with the fast movement of the storms should keep
the flooding potential low along the Gulf Coast and Deep South. The
moisture moving in off the Gulf will be somewhat anomalous for
early December, with PWATs exceeding 1.75 inches along the coast,
or about 2 sigma above normal. A sweeping cold front will allow for
some organization to the storms. With heavy rain in portions of
Southeast Texas over the past 24 hours, locally saturated soils
could favor isolated instances of flash flooding in and around the Houston area.

Further east, soils are much drier due to a distinct lack of rainfall...however, this area will have more time before the cold
front sweeps through for storms to train over the same areas. This
is most likely to occur in a corridor from around Pensacola, FL
northeast to south of Atlanta. This area has very high FFGs, so
even here the threat for flash flooding will be low, as a similar
lack of instability should both hold storm intensity in check, and
at least at first the rainfall will be very beneficial by soaking
a parched landscape.

Wegman


Day 2
Valid 12Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The very beginning of a multi-day rainfall event will begin to
unfold Wednesday night along portions of the Upper Texas and
Louisiana Gulf Coasts. For the most part, the guidance for this
time frame suggests most of the heaviest rainfall from
thunderstorms will remain offshore. However, at least some of that
rain could make its way inland. The threat remains sub-Marginal,
but the area will continue to be evaluated for a later introduction
of a Marginal Risk with future updates.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 020755
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
255 AM EST Tue Dec 2 2025

Day 1
Valid 12Z Tue Dec 02 2025 - 12Z Wed Dec 03 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Thu Dec 04 2025 - 12Z Fri Dec 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE
MISSISSIPPI DELTA AND THE CENTRAL GULF COAST...

A strong warm advection regime of deep Gulf moisture will have
developed along the central Gulf Coast on Thursday morning. A polar
high over the Midwest will suppress the northward extent of the
precipitation. A unidirectional WSW flow regime will set up over
all of the Southeastern U.S. with a 170 kt jet streak aligned
roughly along the Ohio Valley, with a longwave positively tilted
trough over the Southwest. Weak impulses of shortwave energy will
eject out of the trough and along the jet streak, locally enhancing
any convection. The primary forcing for precipitation however will
be overrunning, as warm Gulf air tries to lift over the much colder
air mass over much of the eastern U.S. The combination of
unidirectional flow at all levels out of the WSW, overrunning of
anomalously moist air, and some, albeit far from impressive
instability will support training thunderstorms capable of 2 inch
per hour rates. These storms will align in lines parallel to one
another. Those lines will be slow moving, supporting multiple
rounds of training storms over much of southern/southeastern
Louisiana and into coastal Mississippi. NASA Sport imagery shows
soils in much of southern Louisiana to be bone dry, with moisture
levels at single digit percentages as compared with climatology.
Thus, much of the rainfall, especially in areas where it remains
light, will be beneficial for these areas. The Drought Monitor also
shows this area to be in D2/Moderate Drought. Thus, it will take
some time for enough rain to fall to support flash flooding.
However, guidance suggests the New Orleans metro to be in the
bullseye with the greatest chances for prolonged heavy rain. Given
all of the above, the area remains in a Marginal Risk, but the area
in and around New Orleans to the urbanized Mississippi Gulf Coast
will be evaluated for the need for a Slight Risk upgrade with
future updates.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 031138
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
638 AM EST Wed Dec 3 2025

Day 1
Valid 12Z Wed Dec 03 2025 - 12Z Thu Dec 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

CIRA LPW shows the slug of enhanced moisture along the central
Mexican Gulf coast starting to lift northward through the western
Gulf jet under response from the digging mid-level shortwave across
the Four Corners of the Southwest U.S. Twenty to 30kts of southerly
low level flow will advect the moisture north, bring the surface
front toward the central Texas coast through late afternoon into
the evening; CAPE values will rise into the 2000-3000 J/kg range.
As night-falls, stronger isentropic ascent will increase through
depth as the upper-level southwesterly jet stream flow expands and
strengthens providing the solid ascent plane for sufficient
moisture convergence with total PWats over 2" for expanding region
of elevated thunderstorm activity across the central and upper
Texas Coast.

Northward expansion remains the greatest uncertainty but overall
00z CAMs continue denoting solid rainfall rate potential mainly
along and south of the I-10 corridor with cell motions being slow
but also slightly veering to more easterly with solid back-building
potential to allow for some repeating training. HREF probability
driven by the 00z CAMs, still suggest best signals will remain
off-shore but there was also a slight northeastward trend in some
of the convective elements into southwest to south-central LA with
streaks of 2-3" totals. This will retain the solid Marginal Risk
(5-15% coverage) of FFG exceedance with isolated rapid inundation
flooding possible.

Gallina


Day 2
Valid 12Z Fri Dec 05 2025 - 12Z Sat Dec 06 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
GULF COAST...

Upglide/warm-advective elevated convective activity should be
ongoing start of the forecast period (04.12z) across the central
Gulf coast. Steering flow will continue to flatten within fairly
unidirectional west-southwesterly deep layer flow. Right entrance
ascent to 150-170kt jet centered over the Ohio Valley will keep
isentropic moisture flux across the surface front that will
oriented along and south of the coast. A weak mid-level shortwave
will slide from west to east along the southern periphery of the
jet streak maintaining 20-25kt of west-southwesterly 850mb flow
which given 1.75-2" total PWats and modestly unstable ribbon (up to
1000 J/kg) and should maintain the elevated convective
development. Internal training of back-building convective elements
should be the greatest potential for higher rainfall totals across
the Bayous of south-central LA. A slow eastward propagation of the
SSW- NNE oriented line will occur with the translation of the flat
shortwave energy and potentially expand into coastal MS/AL and
perhaps as far as western FL Panhandle by the end of the forecast period.

There remains some north/south spread in placement of heaviest
rainfall cores/training corridor. The GFS continues a traditional
northward bias along with the NAM relative to the ECMWF and other
global guidance; with some suggestion of overall totals in excess
of 5" in spots. Hi-Res CAMs generally trend toward the southern
solutions with heaviest rainfall along and south of I-10, which
appears more plausible given the overall flow orientation (unstable
air upstream over the waters). Still, there is some solid
suggestion of rainfall rates/totals and environmental conditions
that may warrant an upgrade to a Slight Risk, however, the split in
placement and wider overall total rainfall total spread continues
to be too great to delineate one at this time, but will continue to
evaluate with future updates. As such, the broad Marginal from
Galveston Bay to the Pensacola area of FL remains, though have
broadened it slightly northward to account for the latitudinal variance.

Gallina


Day 3
Valid 12Z Fri Dec 05 2025 - 12Z Sat Dec 06 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
GULF COAST THROUGH CENTRAL GEORGIA...

The deep layer unidirectional west-southwesterly flow regime will
remain in place for the day 3 period as well. The subtle, flat
mid-level shortwave feature will be translating quickly across the
South, through the Carolinas and offshore. The connection to the
western Gulf moisture pool/theta-E source will continue to further
narrow and stretch through an elongated isentropic ascent plane in
the wake of the wave draped across SC, central GA toward the
central Gulf coast. By this time period, the ascent across the
front will be fairly oblique and lapse rates will have moderated
toward limited elevated MUCAPE below 500 J/kg...becoming more of
an Atmospheric River with prolonged moderate rates with 24hr totals
of 1-2" across the length of the stream with scattered localized
maxima of 2-3". To be expected, much like the day 2 period, there
remains a latitudinal spread to the placement of the AR stream and
the width of the inherited Marginal Risk reflects this. However, at this
point, FFG exceedance will be more likely in the longer duration
of 6, 12 and 24hr exceedance, with any flash flooding potential
most likely upstream across LA/S AL, where multiple days of
rainfall should saturate the upper soil profiles and FFG values may
be much lower than currently analyzed.

Gallina
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 040825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Thu Dec 4 2025

Day 1
Valid 12Z Thu Dec 04 2025 - 12Z Fri Dec 05 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
GULF COAST...

Upglide/warm-advective elevated convective activity is ongoing this
morning across portions of the central Gulf Coast with localized
hourly totals topping out near an inch or so (per MRMS estimates).
Right entrance ascent to 150-170 kt jet centered over the Ohio
Valley will keep isentropic moisture flux across the surface front
that will remain oriented along and south of the coast. A weak
mid-level shortwave will slide from west to east along the
southern periphery of the jet streak maintaining 20-25kt of west-
southwesterly 850mb flow which given ~1.75" PWs and the potential
for lingering marginal instability (MU CAPE up to 1000 J/kg now,
but forecast to decrease below 500 J/kg later this morning) may
maintain elevated convective development into midday. Internal
training of back-building convective elements will present the
greatest potential for higher rainfall totals across the Bayous of south-central LA.

Hi-Res CAMs are in general good agreement with the heaviest
rainfall along and south of I-10 (where 3" exceedance probs from
both the 00z HREF and experimental REFS are contained). Little
change in the inherited MRGL risk, which will likely be pulled
around midday as convective activity wraps up.

Churchill/Gallina


Day 2
Valid 12Z Fri Dec 05 2025 - 12Z Sat Dec 06 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Churchill


Day 3
Valid 12Z Sat Dec 06 2025 - 12Z Sun Dec 07 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL GULF COAST THROUGH NORTHERN FLORIDA/SOUTHERN GEORGIA
AND FAR SOUTHERN SOUTH CAROLINA...

A quasi-stationary front draped near the FL Panhandle may become
convectively active by Day 3 (particularly late Saturday night into
Sunday morning) with the potential for localized training along the
boundary with nearly unidirectional westerly flow aloft. Maintained
an inherited MRGL risk with instability being the primary limiting
factor, but both global ensembles (GEFS and ECENS) suggest decent
odds of 2" exceedance (which may translate to localized totals as
high as 3-4" with the addition of CAMs in the coming days).

Churchill
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 051504
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1004 AM EST Fri Dec 5 2025

Day 1
Valid 16Z Fri Dec 05 2025 - 12Z Sat Dec 06 2025

The probability of rainfall exceeding flash flood guidance is lessthan 5 percent.

Cook/Churchill


Day 2
Valid 12Z Sat Dec 06 2025 - 12Z Sun Dec 07 2025

The probability of rainfall exceeding flash flood guidance is lessthan 5 percent.

Churchill


Day 3
Valid 12Z Sun Dec 07 2025 - 12Z Mon Dec 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OFTHE FLORIDA PANHANDLE/NORTHERN PENINSULA INTO SOUTHERN GEORGIA...

A quasi-stationary front draped near the FL Panhandle may become
convectively active by Day 3, though uncertainty remains high as
instability still looks to be the main limiting factor. While
manymodels indicate unproblematic rainfall totals, other models
(the 00z GFS in particular) depict the potential for localized
trainingof convective cells along the front with heavy rainfall
within nearly unidirectional westerly flow aloft. Maintained an
inherited MRGL risk for now with localized flash flooding possible
should 3"+totals occur over a short period in a relatively
sensitive area.

Churchill
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 060730
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
230 AM EST Sat Dec 6 2025

Day 1
Valid 12Z Sat Dec 06 2025 - 12Z Sun Dec 07 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 2
Valid 12Z Sun Dec 07 2025 - 12Z Mon Dec 08 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

The inherited Marginal Risk aligned roughly along the
Florida/Georgia line was removed with this update. A stalled out
front over the area will act as a focal point for a corridor of
mostly light to moderate rain through the day Sunday. Instability
will be near zero, so any convection will be brief. Fast storm
motion along the front due to an approaching 130 kt jet will ensure
that any elevated convection will be short-lived. Finally, soils in
the area are well below normal. The dry soils in this area will
support any light rain being soaked right into the soil. This too
will temper any flooding threat. Due to all of the above factors,
the flooding threat was determined to be less than 5 percent, with
the highest risk in the Jacksonville urban area.

Wegman


Day 3
Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

The first in a series of Pacific lows will move into the coast of
the Pacific Northwest on Monday. The combination of multiple days
of heavy rain as low after low moves into the coast will slowly
increase the flooding threat in western Washington and western
Oregon. The slow increase of the flooding threat is due to the
area's general favorability for rainfall to quickly run off,
resulting in a much higher threshold of heavy rain before there
are flooding concerns. The trailing cold front south of a strong
low that will move into British Columbia will be the focus for the
heavy rain as abundant Pacific moisture slams into the coastal
ranges and Cascades through the period. Soil moisture levels in
this area are around normal for this time of year, but repeated
days of heavy rain will cause the soils to saturate entirely. Thus,
once the soils are saturated, all additional rainfall will convert
to runoff very quickly. Moisture from the tropics will track
northeast around the northwestern periphery of an expansive
subtropical high off the California coast. This abundance of
Pacific moisture from the tropics will support the elevated flash
flooding threat over much of the upcoming workweek.

Very few changes were needed to the inherited Marginal and Slight
Risks. The Slight Risk area was trimmed away from Washington's
mountains, as the dominant precipitation type at the higher
elevations will be snow on Monday morning. Both risk areas were
also expanded south across west- central Oregon due to small
southward adjustments in much of the guidance supporting heavy rain
extending further south in Oregon.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 071450
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
950 AM EST Sun Dec 7 2025

Day 1
Valid 16Z Sun Dec 07 2025 - 12Z Mon Dec 08 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Cook/Wegman


Day 2
Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

The first in a series of lows is expected to slam into the coast of
the Pacific Northwest on Monday. While the low centers will track
well north of the area, the trailing cold fronts will be steered
right into the coast and will be the primary forcing for heavy
rain. The deep Pacific and tropical moisture will originate well
west of Hawaii, then track ENE to NE along the northwestern
periphery of a strong, stationary subtropical high parked off the
central California coast. This will act as the "train track"
directing moisture and any front associated with lows well to the
north into the same stretch of coast (Washington and Oregon) for
the next several days. The air mass will feature PWATs of up to
1.25 inches, which is above the 95th percentile of atmospheric
moisture for this part of the world in December. This is also 3
sigma above normal. In other words, there will be plentiful
moisture for the coastal mountains and the fronts to wring out into
the foothills and adjacent valleys in the form of rainfall. For
just this Day 2 period, expect a widespread 3-5 inches of rain in
the Slight Risk area, with the highest amounts into the highest
terrain. For portions of the northern Washington Cascades, where
most of the precipitation falls as snow, it will be measured in
feet. Note all of these statistics are for just this Day 2 period.
Expect several more rounds, albeit slightly weaker than this one,
to impact these same areas over the coming days.

Contrasting the heightened flooding threat will be that the area is
highly resistant to flooding, at least flash flooding, as the area topographically is quite efficient at moving rainfall to the local
rivers and the ocean. Thus, the highest flooding threat is in the
urban areas such as Portland, Olympia and the eastern suburbs of
Seattle. Elsewhere flood-sensitive low lying areas will also be at
greater risk for localized flash flooding. Meanwhile, the rivers
may take a couple days of heavy rainfall to really respond and
potentially threaten bankside communities.

The Slight Risk area was largely unchanged with this update. It
should be noted there was a small northward shift in the latest 00Z
guidance, but so as to not flip-flop the forecast along the
Canadian border and the Juan de Fuca Strait, the Marginal Risk
there was left unchanged so as to allow for another cycle of model
guidance to determine whether the flood risk should be returned to
the Slight category in these areas. For the vast majority of the
area however, the flooding risk remains steady, with no major
changes to the overall rainfall forecast, just where some of the
heavier rainfall amounts may occur.

Wegman


Day 3
Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

The atmospheric river (A.R.) directing a plume of Pacific moisture
into the coast will shift a bit southward through much of the day
and the first part of Tuesday night. This will focus the heaviest
rainfall into Oregon, with a brief break from the steadiest heavy
rain across northern portions of Washington. While this will allow
for a break in the heaviest rainfall for northern Washington, it
will keep the flooding threat elevated for much of western Oregon,
including portions of southwestern Oregon, which will be largely
missed by Monday's rainfall. Rainfall amounts come down a touch
compared to Monday, with a broad 2-4 inches of new rain expected
into the Oregon coastal ranges as well as the Oregon and far
southern Washington Cascades. Given the rain that is likely to have
impacted this area on Monday, by Tuesday the slightly lesser amount
of new rain will be well offset by the higher stream, creek, and
river levels from the coast to the Western Cascades. Thus, the
inherited Slight Risk for this area remains on track. Due to the
aforementioned southward shift in location, the Slight was expanded
south further into west-central Oregon. However, the risk areas
were unchanged into Washington as the 1-3 inches of rain expected
there should still cause isolated to widely scattered instances of
flash flooding since it closely follows Monday's heavy rains over
much of the western half of the state. 50 kt orthogonal flow of
PWATs at or even a bit above 1.25 inches will still be nearly ideal
for producing upslope heavy rain on the west facing slopes of the
Oregon coastal ranges and Cascades, which will continue to support
the heavy rain threat.

The large subtropical high centered well off the California coast
will continue to be the steering mechanism for the atmospheric
river. This high will be nudged south to allow for the heavy rain
to primary impact Oregon on Tuesday, but this shift will be short-
lived as the high begins to advance back to the north as soon as
Tuesday night, which will gradually shift the atmospheric river
back into Washington.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 080815
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
315 AM EST Mon Dec 8 2025

Day 1 Valid 12Z Mon Dec 08 2025 - 12Z Tue Dec 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The inherited Slight Risk across Western Washington and Oregon
remains little changed this morning. A hauling 150+ kt upper level
jet will bring a vigorous shortwave trough into British Columbia
north of the Canadian border Monday afternoon and evening. The
trailing front associated with the surface low that is being
strengthened by that shortwave will plow into the coast Monday
afternoon. Behind that disturbance, mid-level 850 mb flow will
rapidly increase out of the due west at at least 50 kt, while PWATs
also rapidly increase from 0.75 inches to 1.25 inches as the head
of the incoming atmospheric river (A.R.) makes its way ashore. On
the synoptic scale, the overall rainfall footprint will be greatest
today as compared with the expected rainfall over the next few
days. This in turn will set the stage for multiple days of flooding
concerns as the rain continues through much of the upcoming
workweek. For 24 hour rainfall totals, expect a widespread 4-6
inches of rain for this period for much of the upslope areas of the Olympics/Coastal Ranges/Cascades. The typical downslope areas in
due westerly flow, which includes metro Seattle and Portland,
should be spared the heaviest rainfall, with totals in the 1-2 inch
range in those metros likely to be more common. Soils in these
areas are already near saturation, which represents an average
amount of soil moisture going into today's big rainfall event, so
at least the second half of the rainfall should largely convert to
runoff, leading to significant rises in streams, creeks, and
eventually the rivers that drain the Willamette and Puget Sound areas.

The abundance of Pacific moisture that will be moving into the
Pacific Northwest with the atmospheric river is originating from
the tropics well west of Hawaii. This plume of moisture is moving
over multiple thousands of miles of Pacific Ocean before it reaches
the coast, which is further enhancing the amount of moisture
available to fall as rain once that moisture plume runs into the
wall of mountains that is the coastal ranges and the Cascades.
Strong subtropical high pressure centered off the California coast
is directing the moisture plume's south side around its
northwestern periphery, while strong Pacific lows are drawing the
moisture northeastward on the plumes north side. This is acting to
focus locally enhance the rainfall within the moisture
plume/atmospheric river, which is why the heavy rain is
concentrated into western Washington and Oregon.

Expect that there will be a bit more "slop-over" of rainfall onto
the immediate downwind side of the Cascades and Olympics, so a few
minor expansions of the Marginal were made to include some of the
east-facing slopes of the Cascades, and a Slight Risk area
expansion was made on the east side of the Olympics.

...Northern Idaho and Adjacent Areas...

The inherited Marginal Risk was adjusted slightly to account for
small changes in the expected rainfall across interior areas of the
Pacific Northwest. The Marginal was trimmed from the Glacier N.P.
area due to most of the precipitation expected to fall as snow, but
expanded into far southeastern Washington and far northeastern
Oregon, where upslope potential will be increased in the terrain of
those areas. The A.R. will feature warm conditions, which will
raise snow levels to several thousand feet above ground level,
assuring that except in the highest elevations, the precipitation
type will be all rain, especially west of the Continental Divide.
While today should also bring the most rain to the area compared to
the upcoming several days, all of the soils in this area are nearly
saturated. In fact, recent colder weather and lower snow levels may
locally enhance the flash flooding threat once the heavier rain and
warmer temperatures move in as snowmelt becomes a contributing
factor to rising stream and river levels.

Wegman


Day 2 Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The atmospheric river (A.R.) plume on Tuesday morning will be
aimed at the northwestern quadrant of Oregon, after the plume
shifts south down the coast Monday night. The A.R. will remain
across northwestern Oregon for much of the day Tuesday. Expect an
additional 3-5 inches of rain across the west facing slopes of both
the coastal ranges and the Oregon and far southern Washington
Cascades during the day Tuesday. This will have followed the
roughly 3-5 inches of rain expected Monday night. Thus, expect high
creek, stream, and river levels by Tuesday night after all that
rainfall, as well as low-lying and urban flooding impacts. The
Slight Risk area remains largely unchanged.

By Tuesday night, a much weaker low than Monday's will track
northeast into British Columbia. This low will draw the A.R. back
towards the north before its trailing cold front plows into the
coast. This will reignite the heavy rainfall across much of western
Washington State, while rain rates trail off across west-central
Oregon. Unfortunately the heavy rain will continue into the coastal
ranges and far northern Oregon Cascades through the period. Expect
another 1-3 inches of rain along the Columbia River Tuesday night.
Rain rates will be notably lower than on Monday due to the weaker
low and a slightly weaker onshore flow at 850 (40-50 kts). Due to
the return of steady rain across the Olympics and central Cascades
Tuesday night, the inherited Slight Risk area was expanded north to
include portions of those ranges and their foothills. Meanwhile,
the highest peaks of the Cascades should still remain cold enough
for mostly snow.

...Northern Idaho and Adjacent Areas...

Weakening, but continuous 20-40 kt westerly flow at 850 across the
plains of eastern Washington will allow for locally heavy upslope
rain to continue into much of northern Idaho and northeastern
Oregon. The inherited Marginal is little changed, and mostly
reflects carving out the highest peaks expected to remain all or
mostly snow, while expanding into low lying areas where forecast
rainfall has increased. Regardless, snow levels will remain plenty
high enough to ensure all populated lower lying areas remain all
rain, and thus continue to pose a flooding threat.

Wegman


Day 3 Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Washington and Oregon...

The Slight Risk across portions of the Pacific Northwest remains
largely unchanged with this update. A northwest to southeast
oriented jet stream will remain in place from southern British
Columbia through to the northern Plains. This will put the Pacific
Northwest in the favorable right entrance region of the jet. A
series of upper level shortwaves will zip down the jet, which in
turn will keep the atmospheric river (A.R.) plume in place and
barely moving through the entire period. Due to the flow
orientation changing to out of the west-northwest. The moisture
will flow largely unimpeded through the Strait of Juan de Fuca and
past the coastal/Olympic ranges and into the Cascades. Thus, the
rainfall footprint is much more heavily skewed towards the Cascades
getting much heavier rainfall than the windward side of the coastal
ranges. That said, it will hardly be dry along the coast. Expect an
additional 3-5 inches of rain in the foothills of all of the
Washington Cascades through the period, while the coastal ranges
can expect just 1-3 inches of new rainfall. Given this setup, it
appears the most likely day where a future upgrade may be needed to
the ERO risk areas will be on Wednesday. This of course will be in
no small part due to the antecedent rainfall in nearly all areas
from both Monday and Tuesday, compounding high water concerns day by day.

...Northern Idaho and Adjacent Areas...

A secondary peak of heavy precipitation into northern Idaho is
expected on Wednesday. The same A.R. impacting areas further west
will continue into the interior of the Pacific Northwest on
Wednesday as well. Renewed upslope flow into the west facing slopes
of the Rockies will re-enhance precipitation rates, as well as
raise snow levels after having crashed due to a brief cold air
intrusion on Tuesday. Thus, expect another round of snowmelt to go
along with the heavier rainfall rates. Just as further west, here
too the forecast will need to be monitored for a potential Slight
Risk upgrade with future updates. A large contributing factor to
the need for upgrades in both areas will be seeing what impacts
there are from the heavy rainfall expected especially today, but
possibly also again on Tuesday.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 090821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Tue Dec 9 2025

Day 1 Valid 12Z Tue Dec 09 2025 - 12Z Wed Dec 10 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
PACIFIC NORTHWEST...

...Western Oregon and Washington...

The atmospheric river (A.R.) event is well underway across the
Pacific Northwest this morning. The plume of anomalous moisture
associated with the A.R. is currently aligned across northwestern
Oregon. Radar indicates rainfall rates are between 1/4 inch and 1/2
inch per hour. As is fairly typical of most A.R.s, the impact from
the rain isn't necessarily from the instantaneous rates from heavy
rain, but rather the long duration of steady rain, which can be
heavy at times on the windward (west-facing) sides of the coastal
ranges and the Cascades. A strong and vertically stacked
subtropical high is parked well off the California coast.
Meanwhile, frequent lows are tracking northeast across the
northeastern Pacific and slamming into the Canadian coast. The
trailing cold fronts are tapping into the plume of moisture that is
riding the gradient between the strong high to the south and the
lows to the north.

A Pacific low moved into the British Columbia coast earlier this
evening. This shoved the A.R. to its current position into
northwestern Oregon. As the next low tracks a little further north,
the subtropical high will begin ridging towards the north in
response. This will push the A.R. north with time. A moving A.R. is
usually a very good thing, as it reduces the time it's heavily
raining in any one area. Unfortunately this time, it will simply
move the A.R. back to the already hard hit areas of western
Washington that were hard hit yesterday. This northward shift is
expected this evening as the low moves ashore near Haida Gwaii, or
just south of the southern Alaska Panhandle. As the trailing front
follows into the Washington coast tonight, rainfall rates will
increase significantly as the A.R. aligns into Washington. This
will allow the rain rates to diminish substantially in most of
Oregon, though light rain near the Columbia River is likely to
continue to some much lesser degree. The A.R. is characterized by
PWATs to 1.25 inches, which is between 2 and 3 sigma above normal
for this time of year. Orthogonal westerly flow into the mountains
at 40-50 kt, which is plenty strong enough for substantial upslope
enhancement.

In Oregon, expect the heavy rain, ongoing at present, to continue
for much of the day, while gradually shifting north and weakening.
In Washington the heaviest rain will be overnight tonight. The
Slight Risk area was expanded north with this update to include all
of the Olympic Peninsula as well as for a portion of the foothills
of the Cascades east of Seattle. The surrounding Marginal was
trimmed on the southern end in central Oregon as the trend
throughout the period will be a northward readjustment of the A.R.

...Northern Idaho and Adjacent Areas...

The Marginal Risk into northern Idaho, a small sliver of far
western Montana, and the northeast corner of Oregon is largely
unchanged with this update. Over the last 24 hours, the area has
seen anywhere from 1-1.5 inches of rain. At least that much is
expected over many of the same areas of the Sawtooths, Bitterroots,
and west into northeastern Oregon. Since the A.R. is originating
from the tropics, in addition to the anomalous moisture, much
warmer air will also accompany the rain, causing snow levels to
rise. Expect a significant snowmelt contribution to the rising
streams and rivers as a result. A Slight Risk upgrade may become
necessary if rainfall forecasts increase further through the day.
NASA Sport soil moisture analyses show that soils all across
northern Idaho are at saturation, so all new rainfall today will
convert to runoff. The impact of this runoff is unclear, hence the
possibility of a Slight Risk upgrade.

Wegman


Day 2 Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...Western Washington...

The wettest day of the next 3 will be on Wednesday across much of
western Washington. The continuous westerly flow of 40-50 kt at 850
will continue off the Pacific through the day. A vigorous jet
streak to 150 kt will remain just north of Washington before diving southeastward across the upper high Plains. This will keep
Washington in the favorable right entrance region. A series of lows
will barrel into the British Columbia coast, each one keeping the
A.R. plume nearly stationary and highly energetic. Thus, widespread
4-6 inch rainfall totals are expected for the Olympics and the west
facing foothills of the Washington Cascades. As with most A.R.s,
very high snow levels will keep any snow confined to the highest
peaks of the far northern Cascades. This will keep the lion's share
of the expected precipitation as heavy rain for most of the
Cascades and certainly all of the coastal ranges as well. This
being the third day of more-or-less steady rainfall across much of
Washington, especially south of the Puget Sound area means the
soils are well past saturated, and all of the precipitation should
convert to runoff. Further, the high snow levels will promote
snowmelt as well, which will only further raise river levels.
Finally, the lows moving into the British Columbia coast will turn
the surface flow out of the WNW for a time, especially Wednesday
night. This will direct the flow straight down the strait of Juan
the Fuca and put the low-level flow just slightly off from
orthogonal to the mountains, favoring a slight northerly flow of
moisture down the foothills and the Puget Sound Region. This should
temper the downsloping side east of the mountains just a bit,
allowing for more rainfall into Seattle, Olympia, and the Puget
Sound region broadly. Thus, Wednesday and Wednesday night will also
be the wettest day in the urban cities as well.

Given all of the above, the inherited Slight Risk was expanded with
this update to include the Seattle metro and the surrounding areas
around southern Puget Sound with this update. A higher end Slight
was expanded south down the Cascades to near the Columbia
River/Oregon state line. Once the impacts from all the rainfall
seen across Western Washington become more clear, it will be easier
to ascertain what the impacts from this round of heavy rain on
Wednesday are likely to be. A Moderate Risk upgrade may be needed
with future updates or all or a portion of the Cascades and western
foothills with future updates.

...Northern Idaho and Far Western Montana...

The atmospheric river (A.R.) impacting Western Washington on
Wednesday will continue inland and impact the Rockies of northern
Idaho and western Montana as well on Wednesday. Just like further
west, the A.R. will cause snow levels to rise to as high as 8,000
ft. This will introduce a significant snowmelt component to the
resulting runoff from the upslope rainfall. Over the last 24 hours,
the area has picked up between 1-2 inches of rain, causing soils
to become fully saturated. Today, expect even more rain, with 2-3
inch totals expected to be common. The steady rain, snowmelt, and
abnormally warm conditions will increase the risk for avalanches in
the prone areas, especially where a heavy wet snow falls on top of
much weaker snow layers. Also expect an increase in rock and
landslides, as well as rising streams, creeks, rivers, and
localized urban flooding. Given all these expected impacts, a large
portion of northern Idaho and far western Montana were upgraded to
a Slight Risk with this update, and a smaller portion of northern
Idaho along the Montana state line from I-90 south is in a higher
end Slight Risk, as this area is expected to see the highest
rainfall amounts to around 3 inches through the period, almost all
of which falling as rain.

Wegman


Day 3 Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho and Western Montana...

A double upgrade from no risk area to a Slight Risk was introduced
for a portion of northern Idaho, generally south of I-90 and along
the Montana state line with this update. This upgrade was
introduced largely as a continuation of heavy rain from Wednesday
night across this region. Rainfall rates should be gradually
diminishing through the day Thursday, and as far as the heaviest
rain and immediate impacts, the rain on Wednesday should be more
impactful in this region. However, given the steady rain continues
into the day Thursday, the impacts resulting therefrom should also
continue. Meanwhile further east into Montana, a strong Arctic
front pushing south down the Plains should turn all of the
precipitation over central Montana over to snow. Thus, the flooding
threat is largely confined to northern Idaho and far western
Washington where the warm air associated with the A.R. will remain
in place on Thursday. Rock slides, avalanches, low-lying flooding,
sporadic urban impacts, and very high river levels will all be
ongoing Thursday morning over this area, supporting the Slight Risk upgrade.

...Western Washington...

A Marginal Risk was expanded mainly for the Thursday morning time
period across much of western Washington with this update. This
expanded Marginal Risk includes the Seattle metro and the Puget
Sound area more broadly. As with further east, it will be a
continuation of the steady rain from Wednesday night into Thursday
across the area. It's likely a Slight Risk upgrade will be needed,
as the rain looks to take its time until Thursday afternoon to
significantly diminish in intensity. The A.R. event broadly will be
diminishing through this period. A large low well out over the
Pacific will take a more northward track, as compared to its
predecessors, as the pattern amplifies. This will effectively cut
off the A.R. as the moisture plume gets directed north towards the
Gulf of Alaska, and therefore, the flow with the A.R. shifts north
into British Columbia and substantially diminishes.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 100830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Wed Dec 10 2025

Day 1
Valid 12Z Wed Dec 10 2025 - 12Z Thu Dec 11 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF WESTERN
WASHINGTON AS WELL AS FOR PORTIONS OF NORTHERN IDAHO AND FAR
WESTERN MONTANA...

...Western Washington...

An atmospheric river is currently impacting much of Washington
State this morning. The narrow but intense plume of deep tropical
moisture originating from near Hawaii is being drawn northeastward
by a strong subtropical high that is parked off the California
coast. This area of high pressure is forming the southeast side the
atmospheric river. Meanwhile, polar high pressure over the
Aleutians is sending copious Arctic air well to the south through
the North Pacific. This cold air has set up a strong baroclinic
boundary as it runs into the warm air associated with the
subtropical high. Finally, a strong area of low pressure, fed in
part by this same baroclinicity, will move into the British
Columbia coast today. The low and it's trailing cold front moving
into the coast is adding substantial lift to the atmosphere where
the A.R. is located in western Washington. The result of these
various forcings is a "hose" of deep tropical moisture aligned
right into Washington State, then continuing inland through Idaho
and Montana. The low and its front are locally enhancing the rain
rates, especially on the upwind/west-facing slopes of the coastal
ranges and the Cascades. This latest round of heavy rain is coming
after 2+ days of nearly steady rainfall into this same region.
Saturated soils, full rivers, and abundant additional rainfall are
all contributing to flooding concerns through this area.

Heavy rain is likely to continue for much of the day, gradually
diminishing in intensity tonight, but unlikely to stop completely
most anywhere in western Washington. Since the forecast is little
changed, particularly with expected rainfall amounts, the Slight
Risk area is also little changed. A higher end Slight remains in
effect for portions of the western slopes of the Cascades. Very
high snow levels between 8,500 and 9,000 ft are keeping all but the northernmost Cascades as rain. A wedge of colder air trapped in the
northern Cascades are locally keeping snow levels there down closer
to 6,500-7,000 ft. The higher end Slight includes much of the I-90
corridor between Seattle and Snoqualmie Pass. Land and rockslides
remain a concern, and numerous Flood Warnings remain in effect for
much of the western slopes of the Cascades.

...Northern Idaho and Far Western Montana...

The Slight Risk of excessive rainfall also remains in effect for
much of the northern Idaho Panhandle. This includes the I-90
corridor roughly between Coeur d'Alene on the west side to Missoula
on the east side. The strong atmospheric river moving in from the
Pacific will drop the lion's share of its moisture into the coastal
ranges and Cascades. However, plentiful leftover moisture will then
continue east and be re-lifted into the Bitterroots of Idaho and
Montana. While rainfall amounts will be tempered greatly compared
to areas further west, they will still be significantly impactful
for this region, especially when considering it's been raining
off-and-on in this region from this same atmospheric river for the
past 48-72 hours. Thus, soils are saturated and rivers are already
running high in this area. All additional rainfall will convert to
runoff, both worsening and prolonging any resultant flooding
impacts. The area south of I-90 and east of Lewiston with west-
facing slopes will be hardest hit. It is in this area that a higher
end Slight remains in effect.

The heaviest rain across this region will be through the day today,
with some modest diminishing of rainfall rates through tonight.
Regardless, most upslope areas should see steady rainfall
throughout this period.

Wegman


Day 2
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHERN IDAHO...

...Northern Idaho...

Thursday will be the final day of the atmospheric river across all
of the Pacific Northwest, including into Idaho. A fast moving
shortwave trough diving southeast in the jet streak will
reinvigorate the heavy rain across northern Idaho and western
Montana during the day Thursday. This shortwave will also usher in
an Arctic front to the east of the Rockies across much of the rest
of Montana. This much colder and drier air will finally allow
conditions to dry out as upper level ridging shoves what's left of
the A.R. northward into Canada, and a large low well out over the
Pacific cuts off the tropical feed as it moves towards Alaska. The
ceasing of tropical moisture will effectively end the heavy rain
threat everywhere, though lingering flooding is likely to continue
in this area for multiple days to come.

Heavy rain will likely be ongoing across northern Idaho at the
start of the period on Thursday morning. A surface low will form
along the advancing Arctic air, which will draw the Arctic front
south across much of Montana Thursday night, turning what moisture
is left over to snow east of the range, while putting northern
Idaho into the "dry slot", ending the heavy rainfall. While rain
rates may stay elevated for much of the day Thursday across
northern Idaho, the Slight Risk is at least equally for the ongoing
impacts going into the period from the heavy rain that is likely to
occur tonight. Rock and mudslides will remain a threat until
conditions begin to dry out Thursday night, as well as a
continuation of both ongoing flooding and potentially some new
flooding as the rain ends across the area.

...Western Washington...

A Marginal Risk remains in place across portions of Western
Washington, specifically the foothills of the Cascades on Thursday.
The Marginal Risk reflects the end of the heavy rainfall from the
A.R. from Wednesday and Wednesday night...i.e. diminishing rainfall
rates...and the likely much higher impacts that will be ongoing by
then along all of the Washington Cascades. Thus, expect Slight
level impacts over this corridor to continue, but the heavy rain
ending should spell the end of new or worsening impacts going
forward. The Marginal attempts to strike a balance between these
two competing concerns.

Meteorologically, the A.R. will still be in full swing at the start
of the period 12Z Thursday, but as the forcings from inland lows,
rapidly weakening westerly flow orthogonal to the ranges, and
surface high pressure builds in from the south, rain rates will
rapidly diminish through the morning, ending entirely for many
areas of western Washington by Thursday night. Since the tropical
flow responsible for the A.R. will be cut off by Thursday night,
this will be the end of the event for the area, and a much needed
and "mostly" dry period of weather will follow across most of
western Washington, and those areas that do see additional rain
into the weekend will find it will be a fraction of the intensity
that this A.R. produced, and should be essentially non-impactful.

Wegman


Day 3
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 110734
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
234 AM EST Thu Dec 11 2025

Day 1
Valid 12Z Thu Dec 11 2025 - 12Z Fri Dec 12 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WESTERN WASHINGTON AS WELL AS FOR NORTHERN IDAHO INTO FAR WESTERN MONTANA...

...Western Washington...

The multi-day atmospheric river (A.R.) event of much of the past
week will finally conclude across western Washington today.
Northward-building ridging both at the surface and at the jet
stream level will push the remaining moisture plume from the
already weakening A.R. north into Canada, leaving much of western
Washington with residual moisture from the weakening and drying
westerly flow. Heavy rain is ongoing across much of western
Washington, roughly from Tacoma's latitude north. CAMS guidance
shows the rain should progress a bit further south over the next
few hours as a cold front offshore pushes inland. After that it
will stall out, and the rain rates will diminish in place. Thus,
the heaviest rain over the area for this period will be over the
next few hours this morning, followed by tapering through the
afternoon and into tonight.

Record and in some areas historic flooding is ongoing from the
multiple consecutive days of heavy rain with the A.R. Comparatively
speaking, today's rainfall totals won't be anything near previous
days' totals. Nevertheless, the ongoing moderate to heavy rain
across northern Washington will continue to keep river levels up,
or even rising through the morning until rain rates can diminish a
bit. The Marginal Risk therefore is a compromise between the
ongoing highly impactful flooding and steady rain expected to
continue into the morning, and the fact that the second half to
two-thirds of the period should feature only light rain with the
conclusion of the A.R. event. That is to say that for all of the
Marginal Risk area, ongoing major flooding will continue through
today despite the diminishing rain, and precautions and avoidance
of flooded areas should be taken. The Marginal Risk may be able to
be dropped with the evening update.

...Northern Idaho and Far Western Montana...

Continuous steady rain is expected to continue through the entire
period across the Marginal Risk area in northern Idaho and far
western Montana today. While the A.R. is ending out west, it will
take longer to do so for Idaho and Montana as the forcings
supporting the steady rain will persist throughout the period.
Despite the heavy rain on the order of 1-2 inches over the past 24
hours, in addition to the multiple inches that fell in this same
area in days prior, impacts from flooding have been minimal across
this region. Now, with today being the tail end of the A.R., it's
probable that if flooding impacts were to occur, they would happen
today. Thus, balancing these two offsetting factors, and in
coordination with OTX/Spokane, WA forecast office, the inherited
Slight Risk for this region was downgraded. Isolated instances of
flash flooding are still possible given the expectation of another
24 hours or so of steady rain into the west facing slopes of the
Bitterroots. However, given the lack of impacts thus far, it seems
probable that the same trends will continue through tonight. Steady precipitation should taper off soon after the 12Z Friday end time
for the period, as an Arctic air mass further east also works to
transition any remaining rain over to snow.

Wegman


Day 2
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman


Day 3
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 120826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 AM EST Fri Dec 12 2025

Day 1
Valid 12Z Fri Dec 12 2025 - 12Z Sat Dec 13 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 2
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON...

Introduced a Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. Much of the rainfall on Sunday is currently expected to
fall north of the international boarder with rainfall in the
Pacific Northwest not increasing in coverage or intensity until
late in the Day 3 period. The 11/12Z UKMET was most aggressive with
QPF and there were several global models that limited QPF to under
a quarter of an inch. Based on the expected IVT plume increasing
to over 600 at about the time that the flow begins to take on an
on-shore component...am inclined to follow the ensemble idea of
0.75 inches to locally 1.5 inches of precipitation focused in the
terrain. The area is sensitive given the nearly week-long soaking
so any additional rainfall is expected to bring renewed hydrologic
concerns. Given a fairly tight window of opportunity for rainfall
in the Day 3 period and at least some prospect that the arrival of
higher rainfall rates and amounts will occur after 15/12Z...issued
a Marginal Risk for now. Later shifts can adjust if needed.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 130824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
324 AM EST Sat Dec 13 2025

Day 1
Valid 12Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. The models have shown some run to run differences with QPF
but no real clear trend. One consistent signal is that the
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still
points to the idea that rainfall may not increase in coverage or
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow
reaches the coast and begins to take on more of an on- shore
component...am inclined to follow the ensemble idea of 0.75 inches
to locally 1.5 inches of precipitation focused in the terrain. The
area is sensitive given the nearly week-long excessive rainfall
event...so any additional rainfall is expected to bring renewed
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions
about timing of the onset....still think a Marginal Risk is
sufficient for now although later shifts can adjust if needed.

Bann


Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

Areal coverage of rainfall expands and rainrates increase on Monday
as a well defined atmospheric river continues to direct abundant
moisture into the Washington coastal ranges and Cascades that
gradually makes its way southward into Oregon. Given antecedent
conditions from the excessive rainfall event from earlier in the
week plus whatever falls on Day 2...the concern is for renewed
flooding potential in addition to worsening on-going flooding
especially in the terrain with potential for additional landslides
or mudslides. Saw little reason to modify the Slight risk area that
propagated into the Day 3 period from yesterdays Day 4 outlook
especially given the magnitude of the IVT and precipitable water
values forecast by the global models. The focus of the heavy
rainfall should gradually shift southward into an area that did not
receive as much rainfall from the previous atmospheric river.
Opted to extend a Marginal risk area along the coast as far south
as northwestern California more in deference to uncertainty of
timing as to the rainfall amounts.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 140821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
321 AM EST Sun Dec 14 2025

Day 1
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
WESTERN WASHINGTON...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next real push of
moisture approaches later tonight into the early morning hours of
Monday. Any rainfall in Washington before then should be light and
on the periphery of a rain area directed on-shore north of the
international border. By 15/00Z...precipitable water values should
be approaching 1 inch along the coast as 850 mb winds approach the Washington/Oregon coast. Initially the 850 mb winds should have
more of a southerly than a westerly component...but eventually they
do take on a more orthogonal component to the Washington coast
ranges and Olympics. That is when the best chance for any excessive
rainfall is expected. Model guidance remains in the 0.5 to 0.75
inch range with locally 1.5 inches of precipitation focused in the
terrain. While these amounts are pretty modest for this part of the country...the area remains hydrologically sensitive given the
recent heavy to excessive rainfall event from earlier in the week
and even this amount of rainfall could result in renewed hydrologic concerns.

Bann


Day 2
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER WESTERN
WASHINGTON AND NORTHWEST OREGON...

Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades.
IVT values approaching 800 is currently forecast along or near the
Washington coast as the Day 2 period begins...then weakens
somewhat as the axis progresses southward into Oregon. Given
antecedent conditions from the excessive rainfall event from
earlier in the week plus whatever falls on in the Day 1
period...the concern is for renewed flooding potential in addition
to worsening any on- going flooding. Given how water-logged the
soils have been...the potential is there for additional landslides
or mudslides. Saw little reason to modify the Slight risk area too
much...but continued the idea from yesterday in shrinking the
Slight risk area to minimize the overlap with heavy snow areas
(especially in the northern part of the Cascades as depicted by the
WPC Winter Weather desk). That being said...the overall forecast
reasoning changed little given the consistent magnitude of the
IVT/precipitable water values and QPF forecast by the global
models. The focus of the heavy rainfall should gradually shift
southward into an area that did not receive as much rainfall from
the previous atmospheric river.

Introduced a Marginal Risk area mainly focused over the Idaho
panhandle and a small portion of neighboring eastern Washington
mainly for later in the period. The Atmospheric River moisture
plume will be spreading increasing amounts of moisture into the
eastern part of Washington and northern Idaho. Deterministic QPF
approaching an inch is forecast for areas that had hydrologic
problems recently and concern is for additional problems.

Bann


Day 3
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL LINGERING OVER
PARTS OF THE PACIFIC NORTHWEST INTO FAR NORTHWEST CALIFORNIA...

Precipitation lingers from Washington southward along the Cascades
and the coastal ranges into northwest California on Tuesday and
into the early morning hours on Wednesday. With much of that
falling post-frontal and the heavier precipitation amounts falling
in the form of snow in the northern Cascades...will maintain the
Marginal Risk area for the time. Once again the main adjustments to
the outlook areas were to limit the overlap of excessive rainfall
with heavy areas mainly in Washington. The complex terrain of
northern Idaho and northwest MT made it difficult to avoid
overlapping but the idea is for any excessive rainfall to occur at
lower elevation locations in light of lowering thickness vales/snow levels.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 150832
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Mon Dec 15 2025

Day 1
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WASHINGTON AND OREGON TODAY AND TONIGHT...

Overall...the changes were fairly minor as yesterday's Day 2
Excessive Rainfall Outlook propagated into today's Day 1 outlook.
There were a few run to run differences in the deterministic and
probabilistic runs...especially over northeast Washington- northern
Idaho and northwest Montana. The broad forecast reasoning did not
fundamentally shift.

The areal coverage of rainfall expands and rain rates increase
early today as a well defined atmospheric river continues to
direct abundant moisture into the Washington coastal ranges and
Cascades. IVT values in excess of 700 kg per meter per second early
today will be spreading inland but weaken as the axis makes its way
inland and as the axis of best moisture transport gets directed
southward into Oregon. Given antecedent conditions...the forecast
of another 3 or 4 inches in the terrain raises concerns of worsening
any on-going flooding and result in new areas. In
addition...considering how water-logged the soils became in the
recent heavy to excessive rainfall event...the potential is there
for additional landslides or mudslides. Latest guidance still
showed the nose of the moisture plume getting as far east as parts
of eastern Washington....northern Idaho and northwest Montana where
a second and more focused Marginal Risk area remained. The focus
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous atmospheric
river and has had a chance to drain off some of that water.

Bann


Day 2
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California on Tuesday and early Wednesday. Latest
deterministic and ensemble guidance showed the highest QPF in the
complex terrain...rivaling the QPF on Day 1 in some places in
Washington. The main reason for holding with a Marginal Risk area
was due to the lowering snow-levels given post-frontal lowering of heights/thickness values that result in snow. Even so...did expand
the eastern boundary of the Marginal Risk area a bit to the east in
Washington and a portion of nearby Oregon. While this resulted in
some additional overlap with snow areas...the idea was to capture
some of the higher QPF amounts from regions where (presumably) the precipitation started as rain and then transitioned to snow. Tried
to avoid overlap with the Winter Weather Desk snow amounts of 6
inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann


Day 3
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

...THE MARGINAL RISK OF EXCESSIVE RAINFALL AREA LINGERS OVER PARTS
OF THE PACIFIC NORTHWEST. ON WEDNESDAY...

There should be a relative lull in activity across parts of
Washington...Oregon and northern California in the wake of a system
on Tuesday into early Wednesday. Even though there may still be
some rainfall that lingers into Day 3...the Marginal Risk area was
maintained in deference to the approach of the next and seemingly
stronger AR on Day 4 and to account for the possibility that the
guidance could be too slow with the onset of rainfall with this
system. Refer to guidance from the WPC Medium Range Desk for
additional info. Even if the rainfall associated with the next
system does not arrive prior to 12Z Thursday as shown by the
models...any lingering rainfall still has the potential for be
impactful in the most hydrologically sensitive areas.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 160825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
325 AM EST Tue Dec 16 2025

Day 1
Valid 12Z Tue Dec 16 2025 - 12Z Wed Dec 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Maintained the previously issued Marginal Risk area from
Washington southward along the Cascades and the coastal ranges into
northwest California today and tonight. Yet another round of
precipitation will be spreading from west to east across portions
of Washington and Oregon. Cooler air coming in behind the system
should result in mountain snows and rain for the lowlands and
mountain passes today into tonight. There should be a separate area
of mainly rain and some higher level snows that gets directed into
the southwest portion and northwest corner of California with
amounts locally enhanced by orographic influences. The previous
outlook largely covered this scenario so few changes were
needed.Once again...some overlap between the excessive rainfall
areas and mountain snowfall amounts was unavoidable but we tried
to keep the ERO away from the placement of the WPC Winter Weather
Desk snow amounts of 6 inches or greater.

The overall synoptic pattern continued to show the deepest moisture
and broadest coverage of rainfall arriving in association with the
surface cold front around 17/00Z and the diminishing QPF as the
area gets whisked eastward.

Bann


Day 2
Valid 12Z Wed Dec 17 2025 - 12Z Thu Dec 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

QPF from the 16/00Z operational and ensemble guidance continued to
trend down with a correspondingly smaller risk of excessive
rainfall. That...combined with the higher precipitation amounts
being confined to higher elevations in Washington where
precipitation type would mainly be snow...should limit the overall risk
of excessive rainfall to less than 5 percent.

Bann


Day 3
Valid 12Z Thu Dec 18 2025 - 12Z Fri Dec 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER MUCH OF
WESTERN OREGON AND PORTIONS OF ADJOINING STATES...

The next in a series of Atmospheric Rivers will arrive early
Thursday with its axis of greatest moisture transport being
directed primarily along the western coast of Oregon...with maximum
IVT values in excess of 800 kg per meter per second largely being
directed perpendicular into the coastal ranges early in the period.
Global models continue to advertise the possibility of 6 inches or
more of rainfall during the period...and comparing the WPC 24hr
QPF to ARI yielded a broad swath exceeding the 2-5 year return
intervals. It was also worth noting that the highest ARIs were just
to the east of the crest of the Cascades where an axis of 25-100
year exceedance intervals was depicted. This does seem like a
scenario where more spillover into the normally drier downslope
areas is plausible, so could be an impactful event even into some
of those areas. Consequently, the Day 3 excessive rainfall outlook
expanded the Slight Risk eastward in Oregon to cover areas with QPF
in excess of 5 inches and the highest ARI values mentioned above
given the concern for spillover. Snowfall within this area should
be confined to the higher elevations.

Bann
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 310814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 AM EST Wed Dec 31 2025

Day 1
Valid 12Z Wed Dec 31 2025 - 12Z Thu Jan 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

A slow-moving upper level low centered well west of the California
coast will move towards California through the Day 1/New Year's
period. The upper low will remain negatively tilted as it
approaches the coast. This will allow a surface low, already formed
at the start of the period, to move north along the coast.
Southerly winds ahead of the low will drive plentiful Pacific
moisture into southern California. Upslope into the Transverse
Ranges will wring out much of that moisture, resulting in multiple
inches of rainfall, especially New Year's night, into the L.A.
Basin and adjacent Transverse Ranges. Once the center of the
surface low moves north of the Bay Area, its trailing cold front
will move into southern California. This will turn the flow to out
of the southwest, which will further enhance the upslope flow into
the Transverse Ranges, causing heavier rainfall Wednesday night.

The inherited Slight Risk for much of the L.A. Basin and higher-end
Slight for the Transverse Ranges themselves was left largely
unchanged with this update. The forecast weather pattern remains
largely unchanged, with more parallel southeasterly flow into the
Ranges supporting mostly light rain through much of New Year's
Eve and into the evening, then the rain turning heavier around the
stroke of midnight for the L.A. Basin. While soils across Southern
California have dried out a fair bit since the Christmas rainfall
event, both soils and rivers are still running above normal even
several days later. Thus, the renewal of heavy rainfall Wednesday
night should quickly refill any rivers, with much of the lighter
rain during the day Wednesday saturating the soils in time for the
heavier rains Wednesday night to largely convert to runoff. Thus,
the Slight Risk looks to be in good shape, with no major changes to
rainfall amounts expected requiring any further major changes to
the excessive rainfall forecast.

Wegman


Day 2
Valid 12Z Thu Jan 01 2026 - 12Z Fri Jan 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

Heavy rain will be ongoing at the start of the period Thursday
morning across much of southern California. As the upper level
shortwave moves into the coast, the winds will turn out of the
west-southwest, or exactly orthogonal to the Transverse Ranges.
This will maximize the upslope enhancement of the rainfall just as
the maximum forcing is moving ashore. Through 18Z, this period New
Year's morning will be when the heaviest rain of the event is
expected into southern California. PWATs between 1 and 1.25 inches
will be between 3 and 4 sigma above normal for this time of year, a
sign of how much moisture will be available to convert into
rainfall and runoff from the Transverse and to a lesser extent,
Peninsular Ranges. Once the shortwave moves ashore and inland by
Thursday evening, the combination of weakening of both upper level
and surface lows, as well as rapid weakening of the onshore west-
southwesterly flow behind the low, will lead to rapid diminishing
of the rainfall across Southern California, such that by Thursday
evening, little if any rainfall will be left.

The Slight Risk inherited is largely unchanged both from the
previous forecast and from the Day 1/Wednesday Slight Risk area.
Both days' Slight Risks will be splitting the two halves of the
same event, so little should be different. There is a higher-end
Slight in effect for most of the Transverse Ranges from about
Malibu east through San Bernardino. This will largely be for the
morning hours, as once the rain weakens, the flooding threat
associated with additional rainfall should also rapidly diminish,
likely resulting in an early downgrade of the Slight Risk Thursday
afternoon.

Further north, along the track of the aforementioned upper level
shortwave, rainfall will persist for much longer into the northern
Coastal Ranges and much of the Sierra Nevada foothills, especially
those along the Sacramento Valley. However, this area has more
thoroughly recovered from the Christmas rainfall event and also is
better equipped naturally to handle long duration rainfall. As
such, only an isolated flash flooding threat, consistent with the
unchanged Marginal, is expected.

Wegman


Day 3
Valid 12Z Fri Jan 02 2026 - 12Z Sat Jan 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CALIFORNIA...

Light rain over most of northern California from about 06Z Friday
through 18Z Friday will end as another large upper level low begins
to make its way towards northern California and Oregon. This upper
low, while bigger, will be less amplified/elongated as compared
with the last upper low. That should focus most of the rainfall
into northern California. Further, the surface low will be a
vertically stacked one, whose occluded front has wrapped clear
around the low center. It is this occluded front making its way
ashore that will restart any heavier rain into the southward facing
slopes of the coastal ranges, Klamath, and the northern Sierra
Nevada foothills. Rainfall totals will generally fall in the 2-3
inch range in most of the mountains, with around an inch into the
Sacramento Valley. This amount of rain should be enough to raise
river levels with perhaps an isolated instance or two of flash
flooding in some of the flashier creeks and streams, but overall
impacts should still be minimal, despite some precipitation
occurring prior to this on Day 2. Much of northern California is
well-suited to handle rainfall amounts such as these, so widespread
impacts are not expected. The area's forecast will be monitored
for any potential Slight Risk upgrades needed.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 010803
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Thu Jan 1 2026

Day 1
Valid 12Z Thu Jan 01 2026 - 12Z Fri Jan 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN CALIFORNIA...

A 500mb trough with a small, yet potent, closed circulation will
become part of a negatively tilted 200-500mb upper-trough axis
that is partially responsible for the slug of highly anomalous
moisture that will engulf much of the West today. The focus remains
on Southern California where the Transverse Ranges soils remain
quite sensitive in wake of last week's significant flooding. IVT
values are encroaching upon 500 kg/m/s and embedded within SSWrly
flow that is aligned orthogonally to the Transverse Ranges.
Additional forcing will be located along the frontal boundary that
will trigger additional convection over the East Pacific upon
approach. PWATs are forecast to be just over 1.25" off the Southern
California coast through this morning, but around 18Z, a dryslot
in the 700-300mb layer should result in the conclusion of today's
heaviest rainfall. Some lingering heavy rainfall may be possible in
the Peninsular Range east of San Diego beyond 18Z, but most
rainfall around the L.A. region should be just about over (aside
from lingering upslope into the Transverse Ranges).

Latest HREF guidance does show minor instability present (<250
J/kg on average) between 09-18Z, which may be just enough when
taking into account sensitive soils to result in additional flash
flooding in not just the Transverse Ranges, but also the greater
Los Angeles metro area as well. The new 00Z HREF 24-hour QPF
probabilities for surpassing 3" of rainfall peaks around 50% over
the San Bernadino and low chances (15-25) for localized totals
eclipsing 5". Snow levels remain very high, making just about all
of the expected QPF to be in the form of rain. The lack of higher-
end instability is what is keeping the Slight Risk in place, but
make no mistake-- there remains a heightened risk for flash
flooding this morning in Southern CA with rock slides and debris
flows in/around burn scars possible, including urbanized flash flooding.

Farther north, most area have recovered a bit better from last
week's significant rainfall, but the copious amounts of moisture
combined with sufficient synopitc-scale forcing aloft and
supportive upslope flow along the Coastal Range and as far inland
as the Sierra Nevada does suggest a Marginal Risk for flash
flooding is still warranted. The 00Z HREF does show a small area
between Santa Maria and Big Sur where MUCAPE >250 J/kg could
materialize between 15-18Z and foster more potent instantaneous
rainfall rates as convection moves through. Still, the line of
showers and thunderstorms would be progressive and keep the flash
flooding potential to a very localized area.

Mullinax


Day 2
Valid 12Z Fri Jan 02 2026 - 12Z Sat Jan 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CALIFORNIA...

An expansive upper level cutoff low over the Pacific well west of
the northern California coast will approach the northern California
coast Friday night. The occluded front wrapping around a surface
low will be the primary forcing for heavy rainfall into northern
California Friday night. The occluded front will turn the flow a
bit more onshore (southeast before the front to south-southwest
behind it). This will allow the coastal ranges to upslope some of
that moisture, locally enhancing rainfall rates, particularly into
the northern Coastal Ranges and the Klamath Mountains. Some heavy
rain may impact the Bay area and the coastal ranges south from
there in the waning couple hours of the period, assuming the timing
of the front moving into the coast remains unchanged. IVT values
between 500 and 750 kg/ms are far from impressive, and moisture
anomalies rise to around 2 sigma above normal, a common occurrence
in this part of the world, especially the past few weeks. Thus,
with the rainfall event just getting going, coming in in the middle
of the night, and with less-than-impressive dynamics, the Marginal
Risk for much of the central and northern California coast remains
largely unchanged with this update, and the Marginal looks on track.

Wegman


Day 3
Valid 12Z Sat Jan 03 2026 - 12Z Sun Jan 04 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CALIFORNIA...

A series of upper level disturbances rotating around a large upper
level low will impact much of California and the West Coast this
weekend. With each upper level disturbance, there will be a
commensurate surface front that also makes its way ashore into
northern California. The result will be an almost non-stop rain,
especially for upslope areas on southerly flow, as well as for all
of the coastal ranges. That said, each disturbance will briefly
increase rainfall rates, with those rates decreasing back down in
between disturbances. Thus, Saturday's rain looks to be a long-
duration relatively light (for most areas) rain, rather than there
being big concerns on any one area seeing prolonged heavy rain.
Given the area's good ability to drain rainwater quickly, a
Marginal Risk remains in effect for northern California. The area
will continue to be monitored for a possible Slight Risk upgrade
with future updates.

Wegman
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 021540
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1040 AM EST Fri Jan 2 2026

Day 1
Valid 16Z Fri Jan 02 2026 - 12Z Sat Jan 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE CENTRAL
CALIFORNIA COAST NORTHWARD INTO NORTHERN CALIFORNIA...

1600Z Update...

The 12Z HREF guidance supports no changes to the Marginal Risk area
for the central CA coast northward into northern CA. The offshore
upper trough/front will be moving east later today and tonight and
will bring periods of locally heavy inland. Some localized runoff
issues will be possible overnight and early Saturday morning given
moderate to locally heavy rainfall rates (isolated 0.50+"/hour) and
the moist/wet antecedent conditions.

Orrison

Previous discussion...

No major model disagreements with the eastward push of the strong
mid to upper level low off the northern California coast day 1. The
low level southerly flow will strengthen Friday along and ahead of
the associated frontal boundary pushing toward the central to
northern California coast. While PW values are only 1 to 1.5
standard deviations above the mean, the 850-700 mb moisture flux
values are more anomalous, 2-3+ standard deviations above the mean.
Precip should increase in intensity along the northern CA coast
after 0000 UTC Sat, and spread south into coastal central CA in the
0600-1200 UTC time frame. The frontal boundary is expected to be
fairly progressive, limiting very heavy rainfall totals. HREF and
RRFS neighborhood probabilities for .50"+ hourly amounts are
generally less than 30%, with a few localized 60%+ probabilities
along the central CA coast range to the south of Monterey, and
across the northern Sierra. Areal average 1 to 1.5" amounts
expected along the central to northern CA coast and 1.5-2" in the
northern Sierra with isolated heavier totals of 2.5-3"+ possible.
No significant changes made to the previous marginal risk, with
localized runoff issues possible where soils remain fairly
saturated from recent rains, especially across northern CA.

Oravec


Day 2
Valid 12Z Sat Jan 03 2026 - 12Z Sun Jan 04 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN SIERRA AND SOUTHERN CALIFORNIA...

The axis of anomalous 850-700 mb moisture flux values...2 to 4
standard deviations above the mean...along and ahead of the inland
moving frontal boundary at the end of the day 1 period will impact
the upslope areas of the northern Sierra and spread through the
Transverse Ranges of Southern California day 2. The primary change
from the previous outlook was to add a small slight risk area in
the upslope area of the Northern Sierra. HREF neighborhood
probabilities for .50"+ hourly rainfall amounts are fairly
high...50%+ at the beginning of the day 2 period and again in the
2100 UTC Sat to 0000 UTC Sun period. This will result in day 2
rainfall totals of 2-4"+ in a region of fairly saturated soils from
recent heavy rains. No changes of note made to the previous slight
risk area over Southern CA in the vicinity of the Transverse
Range. The south southwesterly low level flow will have a
significant upslope component into the Transverse Ranges during
the first half of day 2. This is reflected in both the HREF and
RRFS .50"+ hourly probabilities which are high, 50-80%+ during this
period. Localized runoff issues are possible where soils remain
fairly saturated from recent heavy rains.

Oravec


Day 3
Valid 12Z Sun Jan 04 2026 - 12Z Mon Jan 05 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE
CALIFORNIA COAST AND IN THE UPSLOPE OF THE SIERRA...

Additional shortwave energy expected to rotate through the mean
trof position along the West coast and inland across California day
3. This will support a continued wet showery pattern with
additional moderate to locally heavy precip totals along much of
the California coast Ranges and into the upslope of the Sierra. A
broad marginal risk area was maintained from the previous outlook
this period with changes mostly to better fit the latest model and
WPC qpf. The slight risk area over Southern California in the
vicinity of the Transverse Range was removed given consensus of
additional moderate totals.

Oravec
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 040830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Sun Jan 4 2026

Day 1
Valid 12Z Sun Jan 04 2026 - 12Z Mon Jan 05 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN SIERRA...

Precipitation is expected to increase in coverage and intensity
Sunday morning across northern to central California as the next
batch of shortwave energy rotates through the mean west coast trof
and inland across central CA. PW values and 850-700 mb moisture
flux are expected to increase Sunday associated with this next
batch of shortwave energy. This will support locally heavy precip
totals along much of the California coast Ranges and into the
upslope of the Sierra. Hourly rainfall rates in the .25-.50" range
possible along the central CA coast and into the upslope of the
northern Sierra. A small slight risk area was maintained in the
upslope of the northern Sierra where model consensus is for
potential of additional 1 to 2" of rain. The HREF probabilities of
3 hr precip exceeding 3 hr FFG values shows an area of 15-30%
probabilities sinking southward along the upslope of the northern
Sierra Sunday where the slight risk area is drawn. Overall, no
changes of note made to the previous outlook for the upcoming day 1 period.

Oravec


Day 2
Valid 12Z Mon Jan 05 2026 - 12Z Tue Jan 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL
TO NORTHERN CALIFORNIA COAST AND NORTHERN CALIFORNIA...

There are large scale differences developing day 2 with the
amplification of a closed low in the base of the mean trof off the
Central to Southern CA coast. The NAM and GFS are showing a more
southwest solution compared to the EC, CMC and UKMET. This farther
southwest solution is resulting in a trend of less precip along
the central CA coast to the south of San Francisco and into the
Northern Sierra in the GFS and NAM as the low level flow has a
much weaker onshore component compared to the EC, CMC and UKMET.
Models often struggle with closed formation downstream of
flattening upper ridges with overall low confidence at the moment.
The latest WPC qpf did trend towards less precip across the central
CA Coast Range and over the Northern Sierra, but not as dry as the
GFS and NAM. Subsequently, the previous marginal risk area was
decreased in size. There may be additional changes needed to the
risk area with future model cycles, depending how the evolution of
the closing off mid to upper level center evolves.

Oravec


Day 3
Valid 12Z Tue Jan 06 2026 - 12Z Wed Jan 07 2026

...THE PROBABILITY OF RAINFALL EXCEEDING FLASH FLOOD GUIDANCE IS
LESS THAN 5 Percent...

Oravec
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 050745
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Mon Jan 5 2026

Day 1
Valid 12Z Mon Jan 05 2026 - 12Z Tue Jan 06 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ALONG THE CENTRAL
TO NORTHERN CALIFORNIA COAST AND NORTHERN CALIFORNIA...

Upper disturbance off the California coast will meander to the
southeast closer to the coastal plain, eventually pinching off the
mean trough centered to the north and closing off into an ULL as it
migrates down near the latitude of the Bay area. Proximity of the
disturbance and prevailing flow will send a modest IVT pulse
(300-400 kg/ms) crashing into the northern CA coastal plain with
some minor protrusion of the IVT signature inland with a secondary
QPF maxima forecast around the Trinity Mountains over into Shasta
National Forest domain. Hi-res deterministic output is pretty
consistent with the axis of heaviest precip focused from the King
Range down towards Santa Rosa, north of the Bay area with the
latest HREF EAS probs for 1" running between 60-90% for much of
that location with another prob max focused near Mount Shasta.

The main threat for this setup is easily over any urbanized zones
and remnant burn scars across northern CA leading to mainly a
lower-end flash flood concern in the grand scheme of the setup. IVT
signature is one that historically yields more isolated flash flood
threats with the primary focus typically aimed at that coastal
urban centered from the Bay area up towards Eureka, and over the
northern valley locations like Redding. This is where the MRGL
risk was maintained during the forecast as the trend for the
southern edge of any heavy rain prospects south of San Jose has all
but disappeared on guidance. It's still something we'll monitor
for any last minute trends back, but guidance favors mainly the
area north of the Bay at this time. Total QPF for the impacted
areas will be between 1.5-3" with a max between 4-5" for the
coastal ranges north of the Bay area, and over the Shasta National Forest.

Kleebauer


Day 2
Valid 12Z Tue Jan 06 2026 - 12Z Wed Jan 07 2026

...The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Kleebauer


Day 3
Valid 12Z Wed Jan 07 2026 - 12Z Thu Jan 08 2026

...The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Kleebauer
$$
--- SBBSecho 3.28-Linux
* Origin: Capitol City Online (618:250/1)

FOUS30 KWBC 061455
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
955 AM EST Tue Jan 6 2026

Day 1
Valid 16Z Tue Jan 06 2026 - 12Z Wed Jan 07 2026

The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Cook/Kleebauer


Day 2
Valid 12Z Wed Jan 07 2026 - 12Z Thu Jan 08 2026

The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Kleebauer


Day 3
Valid 12Z Thu Jan 08 2026 - 12Z Fri Jan 09 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS NORTHERN ILLINOIS...

Surface low over the Southern Plains will spawn and move northeast
through the period with an established meridional flow projected to
usher elevated moisture poleward, even as far north as the Great
Lakes. Instability will be limited, but non-zero across the Mississippi
Valley with relatively modest MUCAPE on the eastern periphery of
the cyclone. PWAT anomalies approaching record territory would
normally spur greater emphasis on heavy precipitation, but the
relative nature of the PWAT anomaly being in January stunts the
maximum potential limiting more widespread nature of flash flood prospects.

That said, north of I-70, grounds are mostly frozen from the long
stretch of sub-freezing temperatures maintaining a lower prospect
for rainfall absorption and a higher propensity for run off. Areas
along and north of I-80 across northern IL has the deeper sub-soil
layers frozen with grounds likely to encounter majority run off
during the period as moderate to locally heavy rainfall spreads
north. In collaboration with the local Chicago WFO, a small MRGL
was maintained across northern IL to account for the local flooding
threat given the parameters of elevated PWATs and higher risk for
run off. Urbanization in this area is also very prevalent, so heavy
rains could even spur some flooding risks due to poor drainage in spots.

Kleebauer
$$
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FOUS30 KWBC 070740
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
240 AM EST Wed Jan 7 2026

Day 1
Valid 12Z Wed Jan 07 2026 - 12Z Thu Jan 08 2026

The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Kleebauer


Day 2
Valid 12Z Thu Jan 08 2026 - 12Z Fri Jan 09 2026

The probability of rainfall exceeding flash flood guidance is
less than 5 percent.

Kleebauer


Day 3
Valid 12Z Fri Jan 09 2026 - 12Z Sat Jan 10 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN OHIO VALLEY INTO THE SOUTHEASTERN U.S...

Large scale amplification of a trough over the Central Rockies into
the Central Plains will generate a broad axis of ascent from the
Mississippi Valley to points eastward with a cold frontal
progression slowly migrating east across the aforementioned areas.
Meridional component of the pattern evolution will benefit from the strengthening mean trough with multiple shortwave ejections
rounding the trough base across the Lower Mississippi Valley,
advancing northeast through the Southeastern U.S. before migrating
into the Tennessee Valley by the end of the D3. Deep moisture plume
ahead of the trough will usher anomalous PWATs on the order of +2
to +4 sigma spanning east TX through much of the Southeast into
the Southern Ohio Valley. Ample shear and deep moist axis will
maintain a prevalent fixture for much of the period with flow
running close to, if not parallel to the frontal axis that will
bisect southwest to northeast across the Lower Mississippi Valley
through Central and Northern MS/AL into TN. Current ensemble trends
favor a rather broad axis of 2-3" precip totals just within the
means with the deterministic output pushing closer to 4-5" with the
maxima focused over central MS up through northern AL to south-
central TN. This aligns well with the pattern evolution progressing
the front into those confines with a multi-wave ejection riding
into the front as they eject out of the broad deep-layer
southwesterly flow situated across the region.

This setup is classic for a winter time flash flood prospect across
this area of the CONUS as broad ascent coupled with ample deep-
layer shear and highly anomalous moisture tends to amplify the
threat for heavy rainfall repeating over the same areas. This is
being forecast within the Southeast and far southern edge of the
Ohio Valley with the ensemble overlap generally in that corridor
from east-central MS to points north and east with a maxima
oriented over northern AL into southern TN. This is likely the area
to watch, however don't be surprised if areas south across the
southern half of MS into parts of LA see a greater heavy convective
signature that tends to crop up in the short range as the
instability maximum tends to verify a bit further south compared
to what global deterministic output has at this lead. For now,
maintained general continuity in the grand scheme, but adjusted the
SLGT and MRGL risks based on QPF trends and alignment with the
greatest potential for training, and elevated theta_E placement.

Kleebauer
$$
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FOUS30 KWBC 080715
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
215 AM EST Thu Jan 8 2026

Day 1
Valid 12Z Thu Jan 08 2026 - 12Z Fri Jan 09 2026

...THERE ARE MARGINAL RISKS FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MIDWEST & LOWER MISSISSIPPI VALLEY...

Midwest/Lower Mississippi Valley...
A strong shortwave preceding the incoming upper level trough is
expected to bring 500+ J/kg of MU CAPE into portions of the region
during the day on Thursday. The 00z NAM's 2000+ J/kg bulls eye in
KS/MO right at the beginning of the period appears unrealistic/too
high based on recent SPC mesoanalysis MU CAPE trends, though its
trailing instability appears more reasonable, reinforced by the 03z
RAP. The mesoscale guidance advertises small areas of a low risk
of 3"+ across portions of KS, MO, IL, IN, and eventually LA and MS
Thursday night/early Friday morning. While precipitable water
values are in the 1-1.25" range for northern areas and 1.5"+ range
for southern areas, the atmosphere should be well saturated. There
appears to be enough instability to realize local hourly amounts of
1.5"+ where a sufficient number of organized thunderstorms are
able to materialize. Right now, that appears to be the biggest
issue. While it has been dry lately, flash flood guidance values
are modest across much of the area, with 3 hour guidance closer to
3" for the Lower Mississippi Valley, 2.5" for portions of KS/MO,
and 2" for IL/IN. The guidance indicates that the heavy rainfall
should move through quickly, so local amounts of 2-3" within a
couple hours could be enough for isolated to widely scattered
issues, particularly in urban areas. This led to the introduction
of Marginal Risk areas for the areas mentioned above.

Roth


Day 2
Valid 12Z Fri Jan 09 2026 - 12Z Sat Jan 10 2026

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE TENNESSEE VALLEY AND DEEP SOUTH...

Lower Mississippi Valley/Southern Appalachians...
A positively tilted trough with minimal eastward progression due to
the parent cyclone's progression northeast will generate a broad
axis of ascent from the Mississippi Valley to points eastward with
a cold frontal progression slowly migrating east. An anomalously
moisture plume ahead of the trough, noteworthy for January and near
summer averages with a range of 1.50-1.75", will be accompanied by
500-1500 J/kg of MU CAPE. Ample shear for convective organization
is expected, with low- level convergence more or less fixed from
the Atchafalya Basin in LA into the southern Appalachians. The
guidance is wet, with local 4-7" totals forecast locally. The
guidance has shifted southwest,. which caused a southwest shift in
the risk areas.

This synoptic setup is classic for a flash flood prospect across
this region. Deep layer southwest flow should lead to cell
training, and enough effective bulk shear exists for mesocyclone
formation. Hourly rain amounts up to 2.5" are possible here, which
would overwhelm urban environments. The 00z HREF for the first half
of the period advertised a 30-35% of 5"+ near Laurel MS, which if
it occurred within a few hours would overwhelm non-urban
environments as well. At the moment, this appears to be a high end
Slight Risk, but it wouldn't be surprising if a Moderate Risk
was considered as we get further inside the mesoscale guidance
window. The eastern bounds of the Marginal Risk area were
coordinated with the RNK/Blacksburg VA, GSP/Greer SC, and
FFC/Peachtree City GA forecast offices.

Roth


Day 3
Valid 12Z Sat Jan 10 2026 - 12Z Sun Jan 11 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN APPALACHIANS...

Heavy rainfall early in the period is expected over what should be
at least partially saturated ground across portions of the
Southern Appalachians before heavy rainfall ejects into the
southern Mid- Atlantic States. Added a Marginal Risk as a
precaution for this reason; the threat not expected to persist past
18z Saturday.

Roth
$$
d
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FOUS30 KWBC 090754
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
254 AM EST Fri Jan 9 2026

Day 1
Valid 12Z Fri Jan 09 2026 - 12Z Sat Jan 10 2026

..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN MISSISSIPPI AND ADJACENT LOUISIANA...

The classic synoptic setup for a winter flash flooding event
continues to slowly adjust to the timing/orientation of the
upstream shortwave over the Southwest U.S. The very strong leading
cyclone across the Great Lakes will continue to zip along to the
east-northeast with well above normal (4 Standard Anomaly/99th
percentile) moisture and flux still streaming across the Ohio and
Tennessee Valley. Ongoing thunderstorms are expected across the
Lower MS Valley as morning surge of Gulf air streams northward
becoming increasingly confluent/convergent well ahead of the
upstream synoptic front in the Plains.

The strong upstream base of the positive tilt trof will be
advancing throughout the day into the Plains, though the upper-
level jet streak also be expanding and strengthening across the
Ozark Plateau into the Ohio River Valley from 110kts to over 150kts
by the end of the forecast period. The trough will also be shearing
into the confluent, increasingly unidirectional low to mid-level
flow allowing for a deep southwest to northeast atmospheric river
from the western Gulf up the Lower Mississippi and through the
Tennessee River Valley into the southern Appalachians/Cumberland
Plateau through the majority of the day. While the low level flow
will be weaker than Thursday, 850-700mb 40-45kts and 1.5-1.75"
total PWat values will allow for high moisture flux convergence and
support efficient rainfall production.

As the trends have slowed the upstream shortwave, this allows for
greater flux of unstable air northward and forcing to
overlap/intersect with 1000-1500 J/kg of MLCAPE across the Coastal
Plain reducing toward 500 J/kg near the southern TN border, pulsing
with northward surges as the shortwave lifts out. This will provide
enough ascent and low level shear for organized bands of
convection that will likely have training elements throughout the
day. Rain-rates of 1.5"/hr are probable though 00z Hi-Res CAMs
support occasional up-ticks to 2"+/hr locally. Combined with the
training profiles, 00z HREF shows solid 15-25% 3"/3hr probability
across Southern MS into far northeast LA, with nearly 50%
neighborhood probability of 5". As such, and in coordination with
local forecast offices, WPC is introducing a small Moderate Risk of
Excessive Rainfall for S MS and adjacent NE LA. It should be
noted, there is solid agreement within the guidance suite of 5-8"
total streaks but there is limited agreement in the placement
particularly west or east.

Thunderstorms will train, but as they move northeast into Middle to
eastern TN and northern and central AL, intensity and rainfall
totals are likely to diminish, given instability will be limited
to 200-300 J/kg. Yet, prolonged duration and sizable totals of 2-4"
are still possible and so the Slight Risk continues to be in place
downstream across much of AL, northern GA, and southeast TN.

Upstream, as the main forcing exits, a secondary axis of
convergence along instability/moisture gradient across eastern
Texas will produce additional, slightly more elevated
thunderstorms. Similar rates of 1.5" to 2"/hr are possible with
some repeating/training tracks across NW LA, though overall
duration and coverage should limit rainfall totals to 2-4" relative
to the Moderate Risk area further southeast. As such, the Slight
Risk was also expanded westward along the axis of best overall
model agreement.

Gallina


Day 2
Valid 12Z Sat Jan 10 2026 - 12Z Sun Jan 11 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN APPALACHIANS...

Heavy rainfall early in the period is expected over what should be
at least partially saturated ground across portions of the
Southern Appalachians before heavy rainfall ejects into the
southern Mid-Atlantic States. Added a Marginal Risk as a
precaution for this reason; the threat not expected to persist past
18z Saturday.

Roth/Gallina


Day 3
Valid 12Z Sun Jan 11 2026 - 12Z Mon Jan 12 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 (five) percent.

Gallina
$$
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FOUS30 KWBC 101057 AAA
QPFERD

Excessive Rainfall Discussion...UPDATED
NWS Weather Prediction Center College Park MD
557 AM EST Sat Jan 10 2026

Day 1
Valid 12Z Sat Jan 10 2026 - 12Z Sun Jan 11 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN APPALACHIANS TO THE GULF COAST...

Update:

Expanded the Marginal Risk area southwest from the initial issuance
based on radar and satellite trends suggesting the risk of
excessive rainfall will persist beyond 12Z. Confined the expanded
Marginal risk along the axis of highest dew[point ahead of a cold
front moving eastward. Signals still suggest a downward trend
fairly early in the day. For additional details...refer to WPC
Mesoscale Precipitation Discussion 0013.

Bann

Previous Discussion...

Heavy rainfall should be on-goingacross portions of the Southern
Appalachians as the Day 1 period. Some of that rainfall will be
falling on at least partially saturated ground which has the
potential to produce flash flooding. The expectation is that the
threat for excessive rainfall should wane by 18Z today as the area
of rain moves out of the region.

Bann


Day 2
Valid 12Z Sun Jan 11 2026 - 12Z Mon Jan 12 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Mon Jan 12 2026 - 12Z Tue Jan 13 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann
$$
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