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

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


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

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

As the strong AR and its associated WAA aloft approaches on
Monday, these values increase to above 6,500 ft in the northern WA
Cascades and above 7,000 ft from Mt. Rainer and points south.
Farther east, snow levels will rise across the northern Rockies as
well, topping 6,000ft in many cases before falling on Tuesday as
the AR orients itself farther south as a shortwave trough ejects
into the northern Plains. Then, snow levels once again rise on
Wednesday as levels increase above 6,000 ft from southern
Washington to west-central MT. Through Wednesday night, 72-hr WPC
probabilities for >18" are high (>70%) across the WA Cascades
above 5,000 ft, as well as parts of western MT, and western WY
above 6,000-7,000 ft. WPC probabilities even show speckled areas of
low-to-moderate chances (20-50%) for localized snowfall totals
>30" in the more remote reaches of these regions through Wednesday.


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

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


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

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


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

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

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

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

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


Mullinax/Snell