Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Fri Sep 28 2018

Valid 00Z Sat Sep 29 2018 - 00Z Tue Oct 02 2018



Days 1/2/3...

...Northern Rockies and High Plains...

Greatest potential for significant snow accumulations is expected
to occur Saturday into early Sunday and focus mainly across the
mountains of northwest Montana, with accumulating snow in several
other ranges.  Precipitation is forecast to redevelop across the
region as low to mid level frontogenesis and easterly flow will
enhance precipitation east of the Divide while a reinforcing shot
of colder air brings snow levels down late Saturday into early
Sun.  Snow in the mountains commences Sat with 700 mb convergence
combining with the low level frontal circulation to generate lift.

WPC probabilities continue to signal the potential for significant
accumulations along the Lewis Range and Glacier National Park,
showing a Slight Risk for accumulations of 8-inches or more during
the Day 2 period.  The models are converging the forecast areas
impacted by the event, so equal weighting was given to each
solution.

Precipitation is expected to wane on day 3 (Monday) as the 500 mb
wave deamplifies in the model forecasts as it crosses the northern
Plains.  The reduced magnitude of low level frontogenesis and
convergence leads to the accumulations being a couple of inches in
parts of western ND and northeast MT.

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

Petersen