Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Tue Oct 13 2020

Valid 00Z Wed Oct 14 2020 - 00Z Sat Oct 17 2020

Day 1-2...

...Pacific Northwest to the Northern Rockies...
Progressive, zonal flow will carry the last in a series of
shortwave troughs across the northern Cascades on Tuesday and then
across the northern Rockies late Tue into the overnight.  Ahead of
a 150kt upper jet streak, this shortwave will help amplify the
longwave trough east of the Continental Divide Wed-Thu.

Ongoing, high elevation snowfall across the WA Cascades and the
northern Rockies will start to wane Tuesday night into Wednesday
as the amplifying wave digs over the Great Plains (and the ensuing
veering, deep-layer northwesterly flow cuts off the direct onshore
moisture connection). Snow levels will drop to 4000-5000ft across
the region Tuesday night.  Day 1 24hr snow probabilities of 8+
inches above 50 percent will be limited to elevations above 6000ft
in the northern WA Cascades, along with the northern Rockies in
northwest MT.

By Day 2, the potential for any additional significant snow
accumulations will likely be confined to the higher elevations of
the western and central MT ranges, as well as the Bighorns in
northern WY.

Day 3...

The probability of receiving at least 6 inches of snow is less
than 10 percent.

The probability of receiving at least a tenth inch of ice is less
than 10 percent during days 1 through 3.

Pereira/Hurley/Jackson