Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
239 AM EST Sun Dec 03 2023

Valid 12Z Sun Dec 03 2023 - 12Z Wed Dec 06 2023

...Cascades to the Northern and Central Rockies...
Day 1...
A well-defined shortwave diving across the northern Rockies
towards the central Plains today will be accompanied by surviving
moisture transport from the Pacific. Terrain enhancement will
allow for heavy snow today throughout the northern Cascades and
mountain ranges of Idaho, Montana, Wyoming, Utah, and Colorado.
Here, WPC probabilities are high (>70%) for at least 8 inches of
snowfall through early Monday. This includes elevations mostly
above 8000 feet.

For the Pacific Northwest, snow levels increase to above 7000 feet
and above pass level today before increasing even more early this
week as the next round of heavy precipitation approaches. Thus,
most impacts should be confined to heavy rain and not additional
snowfall.

...Northern New York and New England... 
Days 1-2... 
A shortwave lifting out of the Plains and over-top a western
Atlantic upper ridge will strengthen a surface low into the lower
Great Lakes this afternoon, before reaching the St Lawrence Valley
tonight. Meanwhile, a coastal low is forecast to track northeast
away from the Mid-Atlantic and east of Atlantic Canada. Models
continue to show notable CAD signature with Canadian high pressure
over Quebec helping to hold cold air in place across portions of
northern New England, which has become slightly more pronounced
with the latest 00z guidance over portions of Maine just inland of
coastal regions. By late Sunday and continuing into Monday, strong
ascent afforded in part by a coupled upper jet and low-to-mid
level frontogenesis will support the development of heavy
precipitation ahead of the parent low. The heaviest accumulations
are expected to center from the White Mountains eastward into
interior western and central Maine.  WPC guidance shows high
probabilities (>80%) for accumulations of 6 inches or more across
this area through Monday. For the Adirondacks and the northern
Greens, lower totals are more likely, with WPC guidance  under 50
percent for accumulations of 6 inches or more. For areas farther
south, including much of Upstate New York and southern New
England, thermal profiles indicate a mostly rain event with
limited to no accumulating snow expected.

...Central Appalachians...
Day 3...
By late Tuesday afternoon and overnight into early Wednesday, a
clipper low pressure system diving southeastward from the Ohio
Valley towards the central Appalachians within a positively tilted
eastern U.S. trough will provide sufficient upslope snow potential
for the Allegheny Mountains of western Maryland and West Virginia.
Current WPC probabilities for at least 4 inches of snow are low
(<20%) through Wednesday morning, but this snowfall potential is
likely to extend beyond the day 3 timeframe.

Snell