Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 AM EDT Wed Oct 26 2022

Valid 12Z Wed Oct 26 2022 - 12Z Sat Oct 29 2022

...Pacific Northwest into the Central Rockies...
Days 1-3...

A shortwave dropping out of the Pacific Northwest will move into
the Southern Rockies embedded within broad cyclonic flow across
the western CONUS. This shortwave is progged to deepen into a
closed low as it reaches the Four-Corners before moving into Texas
with 500mb heights of -3 sigma according to the NAEFS ensemble
tables. This impressive upper low will help expand rapid height
falls across the region, which when combined with downstream
diffluence and a jet structure that will become increasingly
coupled by Thursday, will result in robust deep layer ascent,
primarily across the Central and Southern Rockies. The overlap of
mid and upper level forcing will likely result in surface
cyclogenesis in the lee of the Rockies Wednesday night into
Thursday, with moist easterly flow around this low providing
additional ascent through upslope influences. This will likely
result in some enhanced snowfall rates and accumulations in the CO
Rockies, the San Juans, the Sangre de Cristos, and even into the
Raton Mesa. Periods of moderate to heavy snow are likely D1 and D2
across this region, with WPC probabilities indicate a greater than
60% chance for 6"+ in the CO Rockies today and tonight, with a
10-30% chance for 6"+ in the Sangre de Cristos and onto the Raton
Mesa Thursday before the strong upper low pulls off to the east.

Other moderate to heavy snow is possible within the broad trough
across the west where any weak impulses rotate through the flow
and combine with the cool column. The best chance for 6 inches or
more of snow elsewhere is expected across the WA Cascades on
Thursday where confluent moist flow from the Pacific and a weak
shortwave lead to WPC probabilities of 20-40%.


The probability of significant icing is less than 10 percent
nationwide.

Weiss