Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
433 PM EDT Sat Oct 16 2021

Valid 00Z Sun Oct 17 2021 - 00Z Wed Oct 20 2021


...Pacific Northwest/Northern California, Inter-mountain West
through the Northern Rockies...
Days 2-3...

An deep, positively-tilted trough currently off the BC coast will
amplify as it swings to a neutral tilt upon reaching the into the
Pacific Northwest and Northern California coasts late Sunday. A
well-defined shortwave low will develop on the base of the broader
scale trough over Northern California Sunday night that then
tracks east across the Great Basin and along the CO/WY border
through Tuesday. Precipitation will inland across the Pacific
Northwest and Northern California coasts Sunday afternoon with
snow levels around precip onset in the Cascades of 6000ft before
dropping to around 4000 ft Sunday night before precip shifts
farther inland. Moderate snow probabilities for four or more
inches on Day 1.5 along the OR/CA Cascades and northern Sierra
Nevada, as well as the Warner Mountains in northeastern California.

The upper low moves east across northern Nevada Monday, northern
Utah Monday evening, and along the Wyoming-Colorado border late
Monday night through Tuesday. Favorable upper jet forcing north of
the low center will support organized precipitation, with snow
levels generally 6000ft. This includes the Independence Mountains
in northeastern Nevada on Day 2. On Day 2.5, the Wasatch and Uinta
of northern UT have low probabilities for four or more inches,
with northwestern Wyoming ranges having moderate probabilities for
six or more inches, expanding to the Big Horns and Laramie ranges
for Day 3.


For Days 1-3, the probability of significant icing (0.25 inch or
more) is less than 10 percent.

Jackson