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FOUS11 KWBC 020730
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 AM EST Tue Dec 2 2025

Valid 12Z Tue Dec 02 2025 - 12Z Fri Dec 05 2025


...Mid-Atlantic & Northeast...
Days 1...

...Rapidly deepening coastal low will bring heavy snow to the
interior Mid-Atlantic and Northeast today/tonight...

Low pressure will move off the NC/VA coast this morning and then
track rapidly northeast along the coast, passing inside the 40N/70W
benchmark before lifting into the Canadian Maritimes by Wednesday
morning. The overlap of height falls, a coupled jet streak, and the
latent heat release along the offshore baroclinic gradient will
allow the low to rapidly deepen during this period, spreading
heavy precipitation and gusty winds into the Northeast.

As the low moves up the coast, persistent and impressive moist
isentropic ascent will surge a theta-e ridge northward to support
expanding heavy precipitation. The coincident WAA at 850mb will
produce additional ascent, with intensifying fgen driving some
banded precipitation, but also warm the column aloft as the surface
high pressure retreats rapidly to the east. The guidance has
trended just a bit warmer again overnight, and while most areas
along I-95 and points west will likely start as a brief period of
snow/sleet, any meaningful accumulation is anticipated only well
inland and at higher elevations, especially in southern and central
New England. The big cities from Washington, D.C. to Boston, MA may
start as snow before changing over to rain (and Boston may change
back to snow briefly before the system exits Wednesday morning).
However, well NW, WPC probabilities are high (>70%) for at least 6
inches of snow from the Catskills through the Berkshires, the
Worcester Hills, and across much of southern NH and ME (away from
the immediate coast) where locally as much as 12 inches is possible
(10-30% chance).

Additionally, while most of the freezing rain accompanying this
system is expected to wane before 12Z/Tuesday, an additional 0.1"
of ice is possible (10-30% chance) across the Central Appalachians
in the vicinity of Shenandoah NP.

Key Messages remain in effect for this system and are linked below
(Key Message #3)


...Northern to Southern Rockies...
Days 1-2...

A shortwave digging south out of British Columbia into the
northwestern U.S. will be positioned across the interior Northwest
to begin the forecast period /12z Tuesday/. This shortwave will
continue to move southeast through Wednesday, and may become more
amplified as it drops through the Great Basin in response to
secondary vorticity maxima digging through its base. This will
result in a slowing and amplification of the trough, with
downstream ascent maximizing through height falls, PVA, and
downstream intensifying jet energy, especially as it approaches the
Four Corners Wednesday morning.

Available moisture will generally be modest as reflected by near-
normal PW anomalies, but the overlapped synoptic lift will be more
than sufficient to wring this out as periods of moderate to heavy
snowfall across much of the terrain. At the same time, a wave of
low pressure is progged to drop southeast coincident with the
shortwave trough, and a secondary front will also push south out of
Canada to cool the column while additionally leading to localized
upslope flow. Despite a shallow DGZ noted in regional forecast
soundings, the best ascent is progged to intersect within this
snow growth region to enhance snowfall, and this suggests a broad
swath of moderate snow is likely today and Wednesday across much
of the Rockies.

WPC probabilities D1 for 6+ inches are highest in the terrain above
5000 ft from the Salmon River/Sawtooth Range of ID through the
Absarokas, Little Belts, Tetons, and down into the Park Range and
other CO Rockies. During D2, the highest probabilities shift south
with the shortwave and increase, reaching above 80% for 6+ inches
along much of the Sangre de Cristos where locally 12+ inches is
likely. Additionally, as this shortwave digs south, some moderate
snowfall is likely along the I-25 urban corridor of Colorado,
bringing some notable snow to a region that has yet to experience
much so far this winter.

...Great Lakes & Northeast...
Day 3...

A strong arctic front will race across the Great Lakes Wednesday,
likely reaching Upstate NY by Thursday morning before continuing
into New England and crossing offshore into the Atlantic Thursday
night. Environmental signals continue to appear favorable for snow
squalls along this front as it dives southeast, and the GFS and NAM
SnSQ parameter have both increased tonight, especially from western
PA through northern New England where a significant overlap of
0-2km fgen and SBCAPE as high as 200 J/kg exists in a region of
elevated low-level RH. This suggests increasing confidence in
linear snow squalls, especially Thursday. While snowfall
accumulations from this event will likely be minimal, brief intense
snow rates combined with gusty winds may create dangerous travel
across parts of the northern Great Lakes and interior Northeast.

Weiss


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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_3.png



$$