Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Thu Apr 23 2020

Valid 12Z Thu Apr 23 2020 - 12Z Sun Apr 26 2020


...Northern/Central Rockies...
Days 1-2...

A shortwave embedded in confluent mid-level flow will advect
southeast within the broad eastern CONUS cyclonic flow, to move
atop the Northern and Central Rockies today, before shifting E/SE
and bringing the associated forcing away from the region on Day 2
/Friday/. This shortwave will be accompanied by jet level
diffluence as a 110kt jet streak pivots southeast, placing the
favorable LFQ for ascent atop the ranges as well. The combination
of these two forcings along with with modest low-level upslope
flow behind a cold front will produce periods of moderate omega
through Friday across the terrain. Moisture is expected to be
modest as evidenced by localized pools of 90% mid-level RH, and
the forcing should advect quickly to the southeast, so total
snowfall is likely to be modest, and generally confined above 8000
ft.

WPC probabilities on D1 are high for 6 inches are high from the
Northern Rockies southeast through the terrain of WY, and into the
Rockies of CO, before lowering and shifting southeast D2 leaving
just moderate probabilities for 6 inches in some of the CO Rockies
and Big Horns. Total accumulation may approach 12 inches in a few
locations during the 2 days.


For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Weiss