Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Thu Oct 12 2023

Valid 12Z Thu Oct 12 2023 - 12Z Sun Oct 15 2023

...North Central Rockies into the Black Hills...
Day 1...

A robust winter storm continues to take shape across the northern
Rockies this morning as a narrow upper jet pushes through the Four
Corners region. Snow will continue over the WY mountains through
the day with significant accumulations. In the mid-levels, the
newly closed off 500mb trough will swing across northern CO and
move into the NE Panhandle this evening as surface low pressure
lifts northeastward into and across central NE. As the upper jet
rounds out across CO and punches northeastward, strong upper
divergence will foster lift through the column in tandem with
cooling in the whole layer over eastern WY into the Black Hills of
SD as well as northwestern NE. Strong moisture flux into the
region from the south will wrap around and into the low via the
WCB which should enhance snowfall as temperatures cool to near and
just below freezing overnight into early Friday. Hi-res guidance
shows potential for several inches of snow into the NE Panhandle,
aided by falling overnight, with more intense rates overcoming
mild ground temperatures.

Snowfall will be generous over the terrain in WY, with an
additional foot likely (probabilities >50%) after 12Z today for
the Bighorns, Absarokas, Laramie Mountains, and Wind River Range.
To the east, temperatures will continue to fall during the day and
especially after dark over southwestern SD and northwestern NE.
Over the Black Hills, WPC probabilities for at least 4 inches of
snow are high (>70%) but are much lower over the NE Panhandle
where there is more uncertainty in accumulation. However,
probabilities for at least 2 inches are >50% there with a higher
end potential of a few times that. Impacts via the WSSI are driven
by snow load (highest over the Black Hills) and Blowing Snow with
strong winds tonight in eastern WY to western SD/NE.


Days 2-3...
The probability of significant snowfall is less than 10 percent.

For days 1-3, the probability of significant ice accumulation
across the contiguous U.S. is less than 10 percent.

Fracasso