Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
328 AM EST Wed Dec 01 2021

Valid 12Z Wed Dec 01 2021 - 12Z Sat Dec 04 2021


...Upper Midwest/Great Lakes to the Northeast...
Days 1-3...

The first few days of December will be quite tranquil winter-wise
with virtually no widespread heavy snowfall or significant icing
expected across the CONUS. The main weather systems of interest
will be a couple of clipper systems moving across the northern
tier of the US into the Northeast and New England.

With the main jet dynamics and forcing along or north of the US
border, the next clipper system is progged to stay mostly across
central Canada and north of the Great Lakes today through Thursday
morning with little to no significant snowfall expected. As the
system moves from Quebec into Atlantic Canada Thursday night,
westerly to northwesterly flow in its wake will support lake
effect snows as well as upslope snows across the Adirondacks and
northern New England mountains. Even here, probabilities for 4"
are quite low, under 10 percent, with just moderate probabilities
for 2".

By late in the forecast period /Fri Night-Sat/, another fast
moving clipper low will again track along or north of the US
border with the bulk of the precipitation and accumulating snow in
Canada. The 00Z  guidance does suggest that the low may drop
further south into northern New York or northern New England late
Friday night and could be more favorable for accumulating snow
Friday night into Saturday. For now, the latest WPC probabilities
for heavy snow are very low, under 10 percent.


...Northern WA Cascades...

A shortwave trough is expected to approach Washington State and
B.C. late Friday night into Saturday with a weak area of low
pressure crossing the state during that time. Height falls and a
coupled jet streak bringing forcing for ascent should yield
widespread precipitation to the northern Cascades and Olympics.
Lower snow levels between 3000-4000 ft will support better odds of
accumulating snowfall and the latest WPC probabilities for 4
inches are 30-40 percent with a slight signal for 6 inches for the
higher peaks of the northern Cascades.



For Days 1-3, the probability of significant icing is less than 10
percent.   

Taylor