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

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


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

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


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

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

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

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

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


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

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


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

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


Mullinax/Snell