Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
437 AM EDT Fri Oct 9 2026

Valid 12Z Fri Oct 09 2026 - 12Z Mon Oct 12 2026

...Northern Rockies...
Days 2/3...

The previously outlined scenario remains on track as an upstream
shortwave reinforces a Pacific Northwest upper-trough today,
allowing it to dig and close off over the next 24-48 hours. At the
surface, a strong lee-side cyclone is forecast to develop today in
Alberta, which eventually shifts into the Dakotas tomorrow. Behind
the trailing cold front, a surface ridge indicative of strong cold
air advection will press into the Northern Rockies throughout
Saturday.

As such, precipitation in the Northern Rockies will begin as rain
tomorrow, but will transition to snow as snow levels crash from
8000-9000 feet at the onset of precipitation to 2000-3000 feet by
Saturday evening. Banded snowfall is likely, particularly over
west-central Montana where moderate to heavy blowing snow is
possible near favorable 700 mb frontogenesis and upslope flow.

By late Sunday into Monday, the remnants of Rachel are expected to
quickly approach from the Great Basin. Renewed frontogenetic
forcing beneath well defined right entrance ascent could briefly
reinvigorate snowfall rates in the Northern Rockies, although there
is uncertainty with respect to thermal profiles in the region tied
to the track of Rachel's remains.

Day 3 WPC probabilities for > 6" are 40-60% for eastern slopes of
the Lewis and Flathead Ranges and 50-70% for the Big/Little Belts,
Big Snowy Mtns, and portions of the Montana Absarokas. Accumulating
snow should reach most valley floors over west-central Montana
through this period with 60-80% probabilities for >4" noted
between Great
Falls and Helena, which is also supported by 00Z REFS
probabilities of exceeding 1"/hour rates. The key to this event
remains the placement of mesoscale banding which will overcome the
marginal thermal profiles in place.

The probability of significant ice across the CONUS Days 1-3 is
less than ten percent.


Asherman/Jackson