Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
402 PM EDT Sun Sep 30 2018

Valid 00Z Mon Oct 01 2018 - 00Z Thu Oct 04 2018


Days 1-3...

...Northern Rockies and High Plains...
Mixed precipitation, resulting in some light snow accumulations,
is expected to continue this evening across portions of eastern
Montana and western North Dakota.  With the warm front lifting
north, any significant snowfall threat is forecast to remain north
of the Canadian border on Monday into early Tuesday. 

However, heavy snows may extend south along the Canadian Rockies
into northwest Montana as a well-defined shortwave trough digs
southwest across western Canada into the northwestern U.S. Tuesday
night into Wednesday morning. Falling heights lead to decreasing
snow levels, so rain should change to snow at higher elevations
first.
There are timing differences as to how soon snow develops in the
Rocky Mountain front/Glacier National Park, resulting in a
differences in several inches of snow among various model
solutions. The 700 mb low opens up into a wave and moves steadily
east out of the northern Rockies and across the northern plains,
with succeeding drying and loss of ascent leading to decreasing
coverage/amounts on Wed.

Combined Day 2 plus Day 3 snow amounts show potential for
accumulations of a foot or more in the higher elevations of the
northern sections of Glacier National Park.

The probability of significant icing is less than 10 percent Days
1-3.

Petersen