Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
414 PM EDT Wed Oct 27 2021

Valid 00Z Thu Oct 28 2021 - 00Z Sun Oct 31 2021

...Pacific Northwest and the Northern Rockies...
Days 1-3...

Strong, moisture-laden, onshore flow, along with a returning warm
front will support the return of heavy precipitation to the
Pacific Northwest tonight.  Potential for widespread heavy snow
across the Olympics and northern Cascades will diminish quickly as
snow levels climb from 4000-5000 ft this evening to 8000-10000 ft
by Thursday morning.  A trailing cold front will bring lower snow
levels, but also drier air -- bringing heavy precipitation to an
end on Friday. 

As the cold front pushes east of the northern Rockies Friday night
into Saturday, post-frontal upslope flow enhanced by a wave
developing over the High Plains will support the potential for
heavy snows along the Lewis Range/Glacier National Park in
northwestern Montana where snow levels are expected drop below
2000 ft Saturday morning.  During the Day 3 period, WPC
probabilities for snow accumulations of 4 inches or more increase
to 40-70 percent across this region.

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

Pereira