Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
429 PM EDT Tue Oct 02 2018

Valid 00Z Wed Oct 03 2018 - 00Z Sat Oct 06 2018


Day 1...

...Northern Rockies across the Central US/Canada border...
A potent shortwave will race eastward from Washington spawning
surface cyclogenesis. There is good model consensus in snow along
the border from Montana into North Dakota through through
Wednesday as warm advection aloft drives strong lift. Upslope
enhancement on low-level northeasterly winds is expected to
produce the heaviest amounts in the higher terrain of the northern
Rockies including Glacier National Park, where high probabilities
for up to 1 foot of snow exist by 00 UTC Thursday. The probability
for 4 inches of snow decreases significantly from northeastern
Montana into northern North Dakota.

The probability of significant icing is less than 10 percent.

Day 2...

Return flow developing around high pressure moving into the
Central Plains will increase moisture into the Rockies while a
filling shortwave ejects northeast from southern California.
Temperatures will be generally too warm for snow except in the
highest elevation above 9000 ft in the southern Bitterroot range
as well as the Uinta Mountains.

The probability of significant icing is less than 10 percent.

DAY 3...

...Northern Rockies...
A trough diving from the Pacific Northwest will spawn weak low
pressure which will drop southeast into the northern plains before
dissipating Friday night as it gets absorbed into a more
significant low in the lee of the Rockies. This will result in
mountain snows across the central and northern Rockies. The
highest amounts are likely in the higher terrain of southern
Montana into northwest Wyoming where moderate probabilities exist
for 4 to 8 inches of snow.

The probability of significant icing is less than 10 percent.

Weiss