Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EDT Sun Oct 18 2020

Valid 12Z Sun Oct 18 2020 - 12Z Wed Oct 21 2020


...Montana and northern Wyoming Rockies onto the adjacent High
Plains...
Days 1/2...
A persistent northwesterly jet over the northern Rockies and above
a surface front will continue to periods of snow into Monday
night. The heaviest snow is expected into this evening as a
shortwave, accompanied by a plume of deeper moisture, slides
across the region. Day 1 snow probabilities are high for 6 or more
additional inches for the interior MT Rockies, the Absarokas into
WY and the Big Horns of WY. While periods of snow are expected to
continue into Tuesday, probabilities for heavy amounts decrease as
drier air moves into the region.

...Northern Plains and Upper Midwest...
Days 2/3...
A shortwave currently over the Aleutians will dive southeast over
western Canada Monday and into eastern MT Monday night. Return
flow ahead of this wave should produce some freezing rain risk
over eastern MT particularly late Monday. The wave crosses the
northern Plains Tuesday with warm air advection precip (snow
changing to rain up to around the weak surface low track).
Favorable upper level jet forcing is expected to help produce a
stripe of accumulating snow across North Dakota to northern
Wisconsin.  However, the progressive nature of this system and
bulk of precipitation on a southerly flow is expected should help
limit the potential for widespread heavy accumulations through
Tuesday night.

For Days 1-3, the probability of significant icing is less than 10
percent.

Jackson