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

Valid 00Z Fri Oct 13 2023 - 00Z Mon Oct 16 2023

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

The storm system responsible for today's winter storm in the North
Central Rockies and Black Hills will advance eastward throughout
the afternoon and into this evening. The closed mid-upper low
circulation is quite anomalous for mid-October as NAEFS shows
700mb heights that are three standard deviations below normal over
the Central Plains. Wind speeds are also strong with 35-45 knots
winds in the 850-700mb layer that are above the 90th
climatological percentile from eastern WY and western NE to
southern SD. Periods of moderate-to-heavy snow will continue this
afternoon and into the early evening hours, largely due to
persistent upslope flow. Snowfall rates this afternoon could top
2"/hr according to the Snowband Probability Tracker (SPT) in the
Laramie Range above 8,000ft and the Black Hills above 6,000ft.

Over western NE and eastern WY, strong dynamic cooling will prompt
rain to switch over to snow. With the aforementioned winds
referenced above, wind gusts of 40-50 mph would help to
drastically reduce visibilities to near whiteout conditions. WPC
probabilities for >2" of snowfall in western NE, specifically
north of Scottsbluff, are topping out between around 50%, with
even areas closer to Cheyenne having 20-40% probabilities. Ground
temperatures have been warm enough to limit accumulations, but
hourly snowfall rates >1"/hr could quickly cause problems
overnight. The 12Z HREF does show as much as a 60% chance for
several hours of 1"/hr snowfall rates over the Pine Ridge of NE
and north of I-80 from Kimball to Cheyenne. Just an inch or two of
snow combined with strong wind gusts would result in blowing snow,
dramatic reductions in visibilities, and in general, hazardous
travel conditions.

Latest WSSI charts show Moderate impacts will continue to be felt
in the mountain ranges of WY, southern MT, and the Black Hills
with Snow Load as the primary driver. In the High Plains of
eastern WY and western NE, Blowing Snow is the primary driver
thanks to the combination of 40-50mph wind gusts and snow.
Overnight tonight, snow will taper off from west to east across
the region as the storm system tracks into the Midwest. By Friday
morning, only a few lingering snow showers in the mountains ranges
will remain.


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.


Mullinax