Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 PM EDT Sat Sep 29 2018

Valid 00Z Sun Sep 30 2018 - 00Z Wed Oct 03 2018


Days 1/2...

...Northern Rockies/High Plains...
Increasing low to mid level frontogenesis and upslope flow will
combine with upper divergence maxima ahead of a closed low to
support precipitation across central and western Montana, with
snow levels decreasing as colder air filters in across the region.


Guidance continues to show the heaviest snow accumulations falling
east of the Divide, centering along the Lewis Range/Glacier
National Park in northwest Montana. WPC probabilities show at
least a Slight Risk for accumulations of 8 inches or more during
the Day 1 period. 

The upper level low is forecast to weaken steadily Sunday night
into Monday. Downstream from the deamplifying wave,
light precipitation is expected to spread further east across
central into eastern Montana and western North Dakota late
Saturday into Sunday.  Some light snow accumulations are possible
across portions of central into eastern Montana and western North
Dakota, however marginal boundary layer temperatures and light
liquid precipitation amounts are expected to hamper the potential
for significant snow amounts. 

As the wave departs further east and a shortwave ridge begins to
build, drier conditions can be expected across much of the
northern Plains on Monday. 

The probability of significant icing is less than 10 percent.

Day 3...

The probability of significant snow and/or icing is less than 10
percent.

Petersen