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

Valid 12Z Tue Oct 13 2020 - 12Z 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 will cross the northern Cascades today
and the northern Rockies late Tuesday-Tuesday night. Ahead of a
150kt upper jet streak, this shortwave will help amplify the
longwave trough east of the Continental Divide Wed-Thu.

Widespread, high elevation snowfall across the WA Cascades and the
northern Rockies on Tuesday will start to wane Tuesday night into
Wednesday as the amplifying wave digs over the Great Plains (and
ensuing veering, deep-layer northwesterly flow cuts off the direct
onshore moisture connection). Snow levels climbing to 7000-9000 ft
from west to east ahead of the shortwave will drop to 4000-5000 ft
across the region Tuesday night. Day 1 24hr snow probabilities of
8+ inches above 50% will be limited to elevations above 6000 ft in
the northern WA Cascades along with the northern Rockies in
northwest MT. By day 2, as the ridge builds and the
coverage/intensity of the precip diminishes from west to east, the
24hr probs of 6+ inches will be confined to the far northern
Rockies above 7000 ft in northwest MT.

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.

Hurley/Jackson