493
FOUS11 KWBC 101926
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Fri Oct 10 2025

Valid 00Z Sat Oct 11 2025 - 00Z Tue Oct 14 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The synoptic-scale snapshot
of this setup features a classic "kissing jets" setup aloft
Saturday night with the diffluent left-exit region of a strong
120-140 kt 250mb jet over Utah and the diffluent right-entrance
region of a >100kt 250mb jet over south-central Canada, both
located over western Montana. Guidance across the board indicate
PWAT percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
remains the most amplified of the bunch, while the ECMWF/UKMET/EC-
AIFS are in the middle ground compared to the more overly amplified
GFS and weaker/sheared CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. The antecedent air-mass both ahead of the storm
and trailing behind the system are not exceptionally cold for mid-
October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into early Monday morning. Snowfall rates
could approach 1"/hr in the Lewis Range and around Glacier Nat`l
Park Sunday morning, which could also foster hazardous travel
conditions in nearby passes.

Farther west, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. Snow levels to remain rather low for this time of year
(around and slightly below 4,000 ft) across the WA Cascades along
with favorable upper ascent, which may lead to some light
accumulating snow for the major mountain passes. Most snowfall
accumulations topping 4" are likely to be confined to elevations
above 5,000ft.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat`l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC`s Winter Storm Severity Index (WSSI) shows Minor
Impacts from the Bitterroots and Idaho Panhandle on east through
much of Montana`s mountain ranges and on south through northwest
Wyoming. Some localized Moderate impacts in the higher elevations,
largely impacting passes within these ranges, are possible.


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


Mullinax/Snell







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