Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 PM EST Sun Dec 18 2022

Valid 00Z Mon Dec 19 2022 - 00Z Thu Dec 22 2022


...Great Lakes...
Days 1...
A deep closed-low centered north of the Great Lakes continues to
drift slowly east today.  Ongoing lake effect snow showers are
forecast to continue, with additional locally heavy amounts
expected, especially east of Lake Ontario.  Westerly flow will
continue to support a band of heavy snow impacting the Tug Hill
region tonight into Monday.  Additional accumulations of 4 inches
or more are likely from the Tug Hill into the western Adirondack
foothills, with localized amounts of a foot or more possible in
the Tug Hill.  Snows are expected to diminish as the low shears
out to the east and a shortwave ridge begins to shift east across
the Great Lakes.

...Pacific Northwest & Northern Rockies...
Days 1-3...
A deep closed-low is currently centered over western Canada with a
broad upper trough extending from the Pacific Northwest into the
northern High Plains.  A well-defined shortwave is forecast to
move through the base of the trough on Monday.  This will drive an
arctic airmass farther south, with accumulating snow expected for
portions of the northern Cascades, Blues, and northern Rockies. 
While widespread heavy totals are not expected, some locally heavy
totals are possible for the higher peaks. 

A more amplified and wetter system will begin to impact the region
on Tuesday.  While the heaviest amounts will likely fall in the
mountains, cold air in place is expected to support accumulating
snows across the lowlands of western Washington by early Tuesday. 
In addition to favorable upper forcing, strong low-to-mid level
frontogenesis will support heavy mountain snow spreading east from
the Pacific Northwest into the northern and north-central Rockies
on Wednesday.  By late Wednesday the areas most likely impacted
with heavy accumulations are likely to include the northern
Cascades, the northern Idaho and the western Wyoming ranges.  WPC
PWPF shows high probabilities for two-day snow totals exceeding a
foot for parts of those areas.

The probability of receiving at least 0.10" of freezing rain is
less than 10 percent.

Pereira