Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 PM EDT Mon Oct 18 2021

Valid 00Z Tue Oct 19 2021 - 00Z Fri Oct 22 2021

...Great Basin to the North-central Rockies...
Days 1-2...

An anomalously deep upper level low closing off over central
Nevada this afternoon will work east tonight, reaching far
southern Wyoming, northern Utah, and northern Colorado by 12Z
Tuesday. The favorable upper level support and forcing will drive
widespread precipitation through the day 1 period -- ending 00Z
Wednesday -- across mainly the higher elevations of the Unita
Mountains in northern Utah, the Wind River Range, southern
Absaroka ranges of western Wyoming, and the Laramie Range of
central/eastern WY. The WPC Day 1 probabilities for accumulations
of 4 inches or more are above 80 percent across these areas.
Accumulations exceeding 12 inches will be possible (30 to 60
percent probabilities) across the highest elevations of these
mountain ranges.

For the Day 2 period -- ending 00Z Thursday -- the upper level low
will move toward the front range of CO/WY while low pressure over
northeast Colorado takes hold and tracks northeast. Thermal
profiles on the northwest side in the vicinity of the inverted
trough will support snow with some rain/snow uncertainty over the
lower elevations of western/north-central South Dakota. This is
where some mesoscale banding may produce some locally higher
accumulations, but critical temperatures are still uncertain. WPC
snow probabilities are confined to mainly eastern Wyoming and
western South Dakota higher elevations including the Black Hills,
where probabilities of exceeding 4 inches are between 20 and 40
percent.

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

Taylor