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FOUS11 KWBC 050704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sun Oct 5 2025

Valid 12Z Sun Oct 05 2025 - 12Z Wed Oct 08 2025

...Northern Rockies...
Day 1...

A positively-tilted upper level trough stretching from the northern
Plains to Central California is directing much smaller shortwave
troughs around its periphery. As each shortwave moves across the
area, they`ve been producing an area of rain and higher elevation
snow as a surface low develops in response to the movement of the
individual shortwaves. The first shortwave is moving over the
Dakotas and taking a well-developed surface low along with it. The
surface lows have been taking advantage of an anomalous plume of
moisture from the northern Rockies to the northern Plains. This
abundance of moisture has helped support areas of snow at the
highest elevations. As the low pulls away, there may be a brief
break in the steadiest precipitation into the mountains. Meanwhile,
a second trough, not as strong but still potent, is diving south
across Idaho and will slow and turn eastward across southern
Wyoming by Monday morning. Behind this shortwave a strong polar
high will dive southward, bringing with it a much colder and drier
air mass. The combination of subsidence with the high, and the dry
air will very quickly end the snow from north to south. Into the
Beartooths and Absarokas, enough moisture may hang on to keep much
lighter snow ongoing into Tuesday morning in a few isolated areas.
By Tuesday morning, the entire longwave trough will have moved
eastward, allowing strong ridging to build into the West Coast.
This feature too will act to limit the heaviest precipitation in
all areas as subsidence works to end the snow.

With the overall forecast largely unchanged, we will see the back
edge of the precipitation move southeastward out of Canada and into
Montana by Monday afternoon. While localized upslope is a
possibility, the drier air with the advancing area of surface high
pressure will quickly win out, allowing some areas to get some
sunshine this afternoon.

WPC probabilities for over 8 inches of snow are between 60 and 80
percent for the Bighorns and Wind River Ranges through Monday
morning.

The probability of significant icing is less than 10 percent.


Wegman



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