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

Valid 12Z Mon Oct 18 2021 - 12Z Thu Oct 21 2021

...Great Basin to the North-central Rockies...
Days 1-2...
An upper low closing off over northern California this morning is
forecast to continue east across Nevada today, before moving
across Utah this evening and overnight.  Overall, the forecast
remains similar -- with widespread precipitation, including high
elevation snow, expected across the Great Basin into the
north-central Rockies today into early Tuesday.  As snow levels
drop to 6000-7000 ft in many locations, areas impacted are
forecast to include the Ruby Mountains in northeastern Nevada, the
Uinta Mountains in northern Utah, and the Wind River and southern
Absaroka ranges in western Wyoming.  WPC Day 1 probabilities --
ending 12Z Tuesday -- for accumulations of 4 inches or more are
greater than 70 percent across these areas.  For portions of Uinta
Mountains and Wind River Range, probabilities for accumulations of
8 inches or more are above 50 percent.  Over the past day, models
have trended slightly south with the track of the low -- lowering
probabilities for significant accumulations farther to the north
along the northern Absaroka Range.

On Tuesday, snow is expected to continue well through the morning
along the Absaroka and Wind River ranges as the low moves east
along the Wyoming-Colorado border.  For the Day 2 period -- ending
12Z Wednesday -- WPC probabilities are above 50 percent for
additional accumulations of 4 inches or more across portions of
the region.  Meanwhile, heavy snow will be developing farther east
across portions of the Bighorn, Shirley, and Laramie mountains --
with Day 2 probabilities above 70 percent for accumulations of 4
inches or more for portions of those areas.  Probabilities are
above 50 percent for accumulations of 8 inches or more parts of
the Laramie and southern Bighorn mountains.

For the two day period -- ending 12Z Wednesday -- WPC
probabilities for accumulations of a foot or more are above 50
percent along much of the Wind River range, as well as for
portions of the southern Absaroka, the southern Bighorn, and the
Laramie mountains.


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

Pereira