Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 AM EDT Sun Apr 21 2019

Valid 12Z Sun Apr 21 2019 - 12Z Wed Apr 24 2019

...The mountains from Western Montana south to the Great Basin and
east into the Southern Rockies...
Days 1-3...

A shortwave moving slowly southward into the Great Basin today
produces enhanced low-mid level deformation and convergence within
an area of pooled moisture remaining over western WY.  This should
result in snow showers and accumulating snow in the Wind River and
Tetons through tonight.

On Mon, as the circulation sinks south across UT and the low level
front sinks south across CO, persistent and anomalous Precipitable
water in the CO Rockies,
will produce long duration light to moderate snows.

On Tue, the closed southwest low remains slow moving, with upper
divergence maxima rotating around the circulation in southern CO. 
70 mb convergence maxima should focus additional showers in
northern NM and southern CO early int he period until the upper
trough departs.

Into early next week, snow levels will be quite high. The
accumulations will be in the highest terrain, with local maxima
likely in the mountains of southern MT/WY on day 1, sinking into
the Central Rockies day 2, and focusing in CO/NM on day 3.

Despite overall modest forcing, prolonged snowfall creates
moderate probabilities for 4 inches of snow and low probabilities
for 8 inches in each of the 3 days in the aforementioned areas.
3-day total snowfall may approach 1 foot in the highest terrain of
the Colorado Rockies, San Juans, and CO/NM Sangre De Cristos.

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

Petersen