Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Thu Oct 02 2025 18:27:45

FOUS11 KWBC 021827
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 PM EDT Thu Oct 2 2025

Valid 00Z Fri Oct 03 2025 - 00Z Mon Oct 06 2025

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

Dual shortwaves embedded within amplifying troughing across the
western CONUS will result in the first significant snowfall across
the higher terrain of the Northern Rockies beginning Saturday
night.

A closed low exiting the Great Basin will begin to fill as it
pivots northeast and shear out in the westerlies, reaching the
Northern Plains by 12Z Sunday. Immediately in its wake, a secondary
impulse, albeit of weaker intensity, will drop into the Northern
Rockies, driving additional height falls into portions of MT and
WY. This secondary impulse will be accompanied by a cold front
digging southward at the surface, leading to cooling temperatures
and additional ascent through forced upslope. Although the greatest
moisture (PWs above the 90th percentile according to NAEFS) will
shift steadily northeast away from the region, as a surface low
strengthens over the Northern Plains, at least some theta-e ridging
will pivot westward back into WY at the same time mid-level SW flow
re-ignites over the region downstream of the secondary impulse.
This will provide sufficient moisture to regenerate precipitation,
with much of this turning to snow from the Northern Rockies to the
Absarokas, and into the ranges of NW WY including the Tetons, Big
Horns, and around Yellowstone NP. As snow levels fall to as low as
7000 ft late in the period, WPC probabilities for more than 6
inches of snow climb to above 70% across this region, with locally
as much as 12 inches possible (10-30%) in the highest terrain of
the Big Horns and Absarokas.

The probability of significant icing is less than 10 percent.

Weiss





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