FOUS11 KWBC 100714
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
314 AM EDT Sat Oct 10 2026

Valid 12Z Sat Oct 10 2026 - 12Z Tue Oct 13 2026

...Northern Rockies... Days 1-3...

A mid-level low sinking southward from British Columbia into WA 
will combine with a Pacific shortwave and sink southward into OR 
and NorCal Sunday night into Monday. At the same time, broad SW 
flow will transport moisture from the the subtropics off CA 
including moisture associated with Tropical Storm Rachel. Those 
remnants will move into the Northern Rockies late Sunday into 
Monday. At the surface, low pressure in the Northern Plains will 
continue eastward, allowing colder air to rush southward into 
Montana today. This will set up a modest to locally heavy snow 
event for the terrain with some snow into the valley locations as 
snow levels crash.

Banded precipitation will expand this morning and change from rain
to snow as snow levels crash from 6000-7000 feet this morning to 
3000-4000 feet by this afternoon over western/northwestern MT. Snow
bands are expected to increase in coverage and intensity tonight, 
some of which may be heavy at times. This will aid in cooling the 
column further and bringing snow to the valley floors later 
today/this evening. The 00Z HREF/REFS indicate orographically-
forced snow rates near 1"/hr especially very early Sunday. For Day 
1, WPC probabilities of at least 6 inches of snow are >50% along 
the eastern slopes of the Lewis and Flathead Ranges and >70% for 
the Big/Little Belts, Big Snowy Mtns, and the Anaconda Range.

The cold air shifts south through the rest of western Montana 
through Sunday morning with additional snow bands developing down 
to the Wyoming border. This will be a heavy/wet snow and the WSSI 
shows some moderate impacts from Snow Load over the southern MT 
ranges Sunday into Monday.

As the remnant moisture of Rachel is pulled north-northeastward 
Sunday, a jet streak will pass through the region and help 
invigorate additional snow over western MT. Once again, 00Z REFS 
probs increase over southern MT Sunday afternoon. WPC probabilities
for at least 6 inches of snow Day 2 are >50% for most of the west-
central and southwestern Montana ranges including the Crazy, Red 
Lodge portion of the northern Absarokas, and Gallatin. 

Over WY, snow levels will remain high in the deeper/milder 
moisture plume (around 10,000ft), so only the highest Absarokas and
the Wind River Range will see snow. However, favorable flow and 
plenty of moisture will maximize snowfall in the high terrain where
1-2 ft of snow is expected. 

Snowfall winds down over Montana early Monday and gradually over 
WY into the evening and overnight. 


...Sierra Nevada/Great Basin/Uintas... Days 2-3...

As the western trough drops down the northern CA/NV border on 
Monday, snow levels on the Sierra Nevada drop to around 7000ft with
generally light precip. Probabilities of at least 8 inches of snow
are around 50% on the High Sierra peaks. Overnight Sunday into 
Monday, snow levels will start to lower just a bit over the Great 
Basin and Uintas (8000 to 10,000ft, respectively). A few inches of 
snow is expected on the highest peaks with perhaps >6" over the 
Unitas above 11,000ft. 


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


Fracasso


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