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

Valid 12Z Sat Oct 16 2021 - 12Z Tue Oct 19 2021


...Pacific Northwest/Northern California to the Northern Rockies...
Days 2-3...
An upper ridge centered over the western U.S. today is expected to
give way to an amplifying trough moving into the Pacific Northwest
and Northern California late Sunday into early Monday.  A
well-defined shortwave moving through the base of the broader
scale trough is forecast to move across Northern California, with
a closed low developing over the Great Basin by early Monday. 
Precipitation will spread across the Pacific Northwest and
Northern California Sunday into Monday.  Snow levels are forecast
to be around 6000-7000 ft Sunday morning before dropping to around
4000-5000 ft Sunday night-Monday morning behind the system's cold
front.  This will result in some isolated heavier snow
accumulations along the Cascades and northern Sierra Nevada, as
well as the Warner Mountains in northeastern California.

On Monday, models show the upper low moving east across northern
Nevada into northern Utah before continuing east along the
Wyoming-Colorado border Monday night into Tuesday.  Favorable
upper jet forcing north of the low center is expected to help
support organized precipitation, including some areas of high
elevation snow.  This includes the Independence Mountains in
northeastern Nevada, the Teton and Wind River ranges in western
Wyoming, as well as the Absaroka Range in western Wyoming into
southwestern Montana.  For the Day 3 period -- ending 12Z Tuesday
-- WPC probabilities for snow accumulations of 4 inches or more
are between 40-70 percent across much of these areas. 

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

Pereira