FOUS11 KWBC 090719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Thu Oct 9 2025

Valid 12Z Thu Oct 09 2025 - 12Z Sun Oct 12 2025

...Northern Rockies...
Day 3...

By the end of the short range forecast period (Sunday morning) a
sharp, negatively-tilted upper trough is forecast to impact the
northern Rockies with moderate to heavy precipitation and lowering
snow levels. The upper trough configuration is expected to develop
as a closed-low currently off the coast of the Pacific Northwest
opens up and interacts with a diving shortwave out of British
Columbia. Additionally, this pattern is favorable for increasing
upper jet dynamics and is supported by model guidance depicting a
120-140kt southwesterly jet streak extending from the central
Great Basin to the central/northern Rockies. This places the
northern Rockies in the left-exit region of the upper jet and most
favorable for upper divergence and widespread moderate
precipitation. As the upper trough moves over the region Sat night
(500 mb heights estimated to be just below the 10th climatological
percentile per the 12z NAEFS) snow levels are expected to also fall
below 6,500ft across much of the northern Rockies by early Sunday
and below 5,000ft across the Pacific Northwest, where lighter
precipitation will be located.

The most impactful snowfall through this timeframe is expected to
be located across southwest Montana as moderate precipitation
overlaps with the lowering snow levels. Latest WPC probabilities
for at least 6 inches of snowfall are 20-40% across the high
terrain of southwest Montana above 8,000ft, which is still above
many of the major mountain passes. Additionally, WSSI-P values for
moderate impacts reach 30-40% in these areas primarily due to snow
load concerns.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell



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