FOUS11 KWBC 270723
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 AM EST Sat Dec 27 2025

Valid 12Z Sat Dec 27 2025 - 12Z Tue Dec 30 2025

*** Major Winter Storm for the Upper Midwest/Great Lakes Sunday
Night then into the Northeast Monday ***

...The West... Day 1... Maximum impact level from WSSI: Moderate

A healthy shortwave over the MT Divide this morning will continue
to move east-southeastward as a southern stream positively-tilted
trough (last gasp of the long-lived Atmospheric River event) moves
through the Great Basin into the Four Corners region. Moisture
anomalies are highest (>80th percentile) over the CO Rockies into
the Sangre de Cristos and snowfall amounts will be highest there,
generally above 9000-10,000ft.

On Saturday night the cold front associated with the strong trough
will quickly drop through the central High Plains and produce some
light/banded snow for the Denver metro region into the High
Plains. WPC probabilities for at least 8 inches of snow are highest

50%) above 8000ft or so. Lighter snow will affect the I-25

corridor from Fort Collins to Colorado Springs, but probabilities
for at least 2 inches of snow are generally less than 30%.

...Southeastern New Mexico... Day 3... Maximum impact level from WSSI: Minor

Cold front racing southward from the CO Rockies will leave behind
a sfc-700mb baroclinic zone along the Rio Grande as moisture from
the Pacific will still be directed eastward across northern Mexico. Temperatures may be just cold enough even to the valley floors for
snow to accumulate, aided by an onset time overnight. WPC
probabilities for at least 2 inches of snow are >10% over most of
southeastern NM and across the TX border, and are >50% in the
Sacramento Mountains above 5000ft.

...Great Lakes/Northeast... Days 2-3...
Maximum impact level from WSSI: Major

The potent northern stream trough exiting Montana will close off
as it moves across the northern Plains then digs through Iowa late
Sunday. Upper jet will become more amplified overnight and help aid cyclogenesis across northern IL into Lower MI as pressures rapidly
drop through the 990s into the 980s mb after 00Z Monday. Snow
associated with the approaching cold front from the west will merge
into the developing comma-head snowfall to the northwest of the
sfc low Sunday afternoon along an inverted surface trough and on
the edge of the moisture gradient to the southeast (where PW
anomalies in the warm sector rise to >99th percentile). Snow will
expand and increase in intensity over eastern MN through
central/northern WI into the U.P. of Michigan as winds increase
from the NW to NE, picking up additional moisture from Lake
Superior. The low pressure will continue to deepen as it briefly
slows over northern Lower MI very early Monday awaiting the mid-
level low from the west. Shortly thereafter, it should reach peak
intensity (mid 970s mb) over Lake Huron or Georgian Bay with
continued wrap-around moisture as the WCB wraps up and around the
low. Snowfall will maximize over the northern short of the U.P.
where WPC probabilities of at least 12 inches of snow are >70%. As
the low continues through Ontario to Quebec, CAA will bring lake
effect snow to the rest of the Great Lakes into D3. WPC
probabilities for at least 6 inches of snow D3 are highest south of
Buffalo in the Chautauqua Ridge, aided by a multi-lake connection.
The bombing out of the system will induce strong winds over much
of the region, creating additional hazards due to blowing/drifting snow.

Well ahead of the main surface low, warm air advection will
overrun cold <32F surface temperatures in the central Appalachians
into the Northeast. With precipitation starting overnight, and snow
on the ground through much of the region already, the WAA aloft
will have a tough time reaching the surface. This could result in a
widespread icing event to start for central PA northward into the Adirondacks/eastern NY and much of New England. Without a surface
high to the north, temperatures will have an easier time rising due
to the freezing rain process itself, but counteracted by snow-
covered ground which could act to keep the surface warm front
farther south. It may only be when the cold front (or triple point
low) approaches that the surface inversion mixes above freezing,
albeit briefly. This may be especially true over central/northern
New England as the guidance indicates a triple point low could form
and act to keep northern areas below freezing at the surface. WPC
probabilities for at least 0.10" icing are >50% over parts of north
central PA and from the Catskills northward into the Adirondacks
and eastward through central New England (along/north of the Mass
Pike/495) and into western Maine. Greater than 50% probabilities
for at least 0.25" icing exist over the Adirondacks and into
central VT/NH. Over far northern Maine, though some icing may creep
that far north, snow will be the dominant ptype and WPC
probabilities for at least 4 inches of snow are >50% over the North Woods.

Fracasso

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

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