FOUS11 KWBC 102028
QPFHSD

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

Valid 00Z Sun Oct 11 2026 - 00Z Wed Oct 14 2026

...Northern Rockies...
Days 1-2...

Two rounds will combine for a notable first significant snow of
the season for west-central Montana terrain and valley through
Sunday night.

Ongoing banding over west-central Montana causes further dynamic
cooling, lowering snow levels, and increasing snowfall rates
through this evening. This banded situation then persists over
west-central MT into Sunday morning. Rates lighten for midday
Sunday before shortwave energy containing the remnants of Rachel
shift up the Intermountain West, bringing broad coverage of snow
across western Montana late Sunday afternoon through Sunday night.

Mid-level low over north-central Washington shifts south to
interior Oregon tonight, stretching into a positively-tilted oval
over Oregon/northern California through Monday. Broad
southwesterly flow east of the low continues to transport moisture
from the the subtropic Pacific ahead of Rachel. Those remnants
will shift north over the Intermountain West Sunday and over
Wyoming Sunday night. At the surface, low pressure centered over
the Dakotas will continue to suppress south and east while ridging
from Alberta brings cold air over western Montana through Sunday
night.

12Z HREF mean hourly rates begin to exceed 1"/hr by 00Z in
preferred orographic lift in the Flathead Range and the Big/Little
Belt Mtns. The banding so far has been robust. That should continue
and movement may be small through this evening. The snow level
appears to be rapidly dropping to valley level, so again where the
bands persist, significant snow will occur. Day 1, WPC snow probs
for >6" are >80% along the eastern slopes of the Lewis and
Flathead Ranges then east over the Belts, and 50-70% in the
adjacent terrain down to around 3800ft MSL.

The cold air shifts south through the rest of western Montana
through Sunday with additional snow bands developing down to the
Wyoming border in the morning before tapering off through midday.
This will be a heavy/wet snow and the WSSI continues to have some
moderate impacts for Snow Load over the southern MT ranges for Day
2 and Snow Amount in west-central Montana for Day 1.

As the remnant moisture of Rachel is pulled across Wyoming Sunday,
a jet streak will pass through the region and help invigorate
broad coverage of snow over western MT with some embedded banding.
Day 2 WPC snow probs for >6" Day 2 are >50% for most terrain in 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 highest 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 Ranges/Utah Ranges...
Days 2-3...

As the western trough drops down the northern CA/NV border Sunday
night, snow levels on the Sierra Nevada drop to around 7000ft
before lowering as far as 6000ft as moisture increases through the
Day Monday. Day 2.5 (12Z Mon-12Z Tue) snow probs for >4"
probabilities of at least 8 inches of snow are 30-50% on the High
Sierra peaks and the highest White Mtns.
Snow levels over the Great Basin drop to around 7000ft Monday and
around 9000ft for the Uinta Monday night. Day 2 and 3 snow probs
for >4" are 30-50% for the Great Basin (including Ruby) and
southern Utah ranges) and 50-80% for the Uinta.


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


Jackson


$$
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