Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Thu Dec 02 2021

Valid 12Z Thu Dec 02 2021 - 12Z Sun Dec 05 2021

Pacific Northwest to the Northern Rockies and Northern Plains...
Days 2/3...

Deep low pressure over the Gulf of Alaska will eject southeast
with an dislodging shortwave trough Friday night. A surface low
associated with the shortwave crosses northern Washington Saturday
then re-emerges as a potent surface low shifting east over the
northern Plains late Saturday through Sunday night. A strong
low-to-mid level frontogenesis band, with an expectation for at
least locally heavy snow, sets up north of the low track along the
U.S.-Canada border from central Montana through northern
Minnesota.

Day 2.5 WPC snow probabilities for 6 or more inches are moderately
high over the WA Cascades and northwest Montana ranges including
the Lewis Range/Glacier NP. Then on Day 3 the 6 or more inches
probabilities are 20 to 60% across northern North Dakota into
northern Minnesota. There is a risk for light icing on the
southern end of the precip swath near the low center, particularly
over northeastern Montana on Saturday.


...Great Lakes to the Northeast...
Days 1-3...

Low pressure over Ontario this morning will shift east across
Quebec through tonight, allowing winds over New England to veer
westerly to northwesterly and support upslope snows across the
northern Adirondacks, Green and White mountains, but with
accumulations of 2" or less.

The next shortwave trough enters western Ontario late Friday and a
slightly more southerly track will take it across central New
England Saturday. Northwesterly winds behind the associated cold
front will bring LES to Lake Superior with Day 2.5 WPC snow
probabilities for 4 or more inches moderately higher over the
eastern U.P. of MI. Then westerly winds are forecast to bring lake
effect back into the Tug Hill of New York later Saturday.


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

Jackson