Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Sat Apr 20 2019

Valid 00Z Sun Apr 21 2019 - 00Z 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 onshore California tonight will begin to drop
southward towards the Great Basin Sunday and then close off while
embedded within a positively tilted longwave trough over the
Southwest through much of the forecast period. This feature will
be accompanied by favorable upper diffluence, first within the RRQ
of a departing upper jet Sunday, and then within the LFQ of a
secondary jet max rotating through the trough Monday into Tuesday.
These features together with persistent and anomalous PWAT across
the western mountains, along with modest mid-level frontogenesis
as a cold front sags southward will produce long duration moderate
snows.

Throughout the weekend and into early next week, snow levels will
be quite high, only as low as 6000 ft near the Canada border on
Day 1, and rising to as high as 10,000 ft by day 3 across the
Southern Rockies as ridging blossoms atop the weakening low in the
Southwest. This suggests the best accumulations will be in the
highest terrain, with local maxima in accumulations likely in
ID/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 8 inches of
snow 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.

Weiss