Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
421 PM EDT Mon Oct 12 2020

Valid 00Z Tue Oct 13 2020 - 00Z Fri Oct 16 2020

Days 1-2...

...Pacific Northwest to the Northern Rockies...
The final shortwave trough in a series of impulses in zonal flow
into the Pacific Northwest reaches Vancouver Island and the
Olympic Peninsula late tonight and cross the far northern Rockies
late Tuesday.

High elevation snowfall coverage picks up again late tonight over
the WA Cascades and through the day Tuesday for the northern
Rockies before slowly waning Tuesday night into Wednesday as the
amplifying wave digs over the Great Plains, veering the deep layer
flow northwesterly and cutting off the direct onshore moisture
connection. Snow levels initially around 5000ft this evening climb
to 8000-9000 ft ahead of the shortwave tonight, then drop to
4500-5500 ft across the WA Cascades Tuesday afternoon and northern
Rockies Tuesday night. Day 1 24hr snow probabilities of 6+ inches
above 50% are limited to the high northern WA Cascades and Day 1.5
for the highest peaks of far northern ID and northwest MT. By Day
2.5 the probabilities substantially drop across the region as
lower snow levels are met by much reduced precip rates.

Day 3...
The probability of receiving at least 6 inches of snow is less
than 10 percent.

Days 1-3...
The probability of receiving at least a tenth inch of ice is less
than 10 percent.

Jackson