760
FOUS11 KWBC 091923
QPFHSD

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

Valid 00Z Fri Oct 10 2025 - 00Z Mon Oct 13 2025

...Northern Rockies...
Day 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 EPS shows a classic
"kissing jets" setup 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. ECMWF 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
plenty of uncertainty with varying solutions on the depth/phasing
of two 500mb disturbances over the Northwest. The GFS is the most
amplified of the bunch but is is more amplified compared to the
GEFS mean, 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. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive 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 Sunday night. 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.

WPC probabilities depict moderate chances (40-60%) for snowfall >8"
in the peaks of the Lewis Range above 7,000ft (including Glacier
Nat`l Park) on south along the Absaroka/Tetons above 8,000ft
through Sunday afternoon. Lighter snowfall accumulations as low as
6,000ft in the Lewis Range/northwest Montana and 7,000ft in the
Absaroka/Tetons are expected. WPC`s Probabilistic Winter Storm
Severity Index (WSSI-P) show similar moderate chances for Minor
Impacts for the event in these mountain ranges. Other mountain
ranges are likely to receive light snow totals (2-4") as far west
as the Bitterroots and as far south as the Teton and Wind River
Ranges in western Wyoming.

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

Mullinax



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