Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EST Mon Dec 15 2025

Valid 12Z Mon Dec 15 2025 - 12Z Thu Dec 18 2025


...Great Lakes...
Day 1...

Some lake enhanced snow for Michigan this morning ahead of a
shortwave trough currently over the Arrowhead of MN. The greater
impacts are on the eastern Great Lakes where flow is already
backing westerly. Brief single-banding LES occurs this afternoon
off Lake Erie into the South Towns of Buffalo where Day 1 PWPF for
>4" are around 60%. The greater LES formation is this evening with
single-banding into the Tug Hill Plateau through the night before
tapering off Tuesday morning in notable warm air advection. The
saturated layer gets into the DGZ and the flow is fairly steady
state, so decent snows are forecast. Day 1 PWPF for >8" are around
80% for the Tug Hill.


...Cascades and Northern Rockies...
Days 1-3...

A lead warm atmospheric river (AR) will bring mostly rain to the
PacNW through early afternoon with very high snow levels around
9000ft. A shortwave trough brings a cold front through by this
evening which will lower snow levels this evening amid lighter QPF
to around 4000ft in WA 5000ft in northern OR. Day 1 PWPF for >8"
are limited to the higher WA Cascades.

Snow levels rise back to 5000ft in WA and 6000ft in OR Tuesday as
the next moisture surge pushes inland. However, a sharper shortwave
trough axis pushes across the Cascades by 12Z Wednesday. This
potent cold front brings a sharp drop in snow levels after 06Z
Wednesday to around 2000ft in WA and 4000ft in OR. Again, the
precip rates rapidly drop with the snow levels, but there should be
impactful snow at pass levels including Snoqualmie. Day 2.5 PWPF
for >8" are over 80% for most of the WA Cascades. Low snow levels
and precip rates persist then through Wednesday night.

Moisture and windy conditions will progress eastward over the
Northern Rockies this afternoon and much more so Tuesday night.
Day 1.5 snow probs for >8" are 30-60% over the northwestern MT
ranges. Day 2.5 snow probs for >8" are 50-80% over the western MT,
central ID, and northwest WY ranges with rapid drops in snow
levels.


The probability of significant icing is less than 10 percent.

Jackson