Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
354 AM EDT Wed Oct 13 2021

Valid 12Z Wed Oct 13 2021 - 12Z Sat Oct 16 2021

...Eastern Montana/Wyoming to the western Dakotas...
Day 1...

Wrapped-up surface cyclone will continue to move northeastward
through the Dakotas today as the surface low reaches its minimum
pressure. Snow will be confined to the northwestern/western side
of the low this morning in the deformation axis within a thermally
marginal environment. Rain/snow line has wavered east-west as
varying intensities of precipitation move through, but snow will
accumulate in areas seeing higher rates during the first part of
the forecast period. By later this afternoon, the snow will wind
down and pull eastward/diminish as the low moves farther away from
the area. Day 1 WPC probabilities for 4 or more inches of snow are
40-80% over southeastern Montana into the Black Hills. 


...Colorado...
Day 2...

A strung out shortwave at the nose of the North Pacific jet will
dig into Utah by the start of Day 2 (12Z Thu). Westerly flow will
capitalize on upslope enhancement over central Colorado ranges
where WPC probabilities of at least 4 inches of snow are 30 to 70
percent, generally above 9-10,000 ft. Furthermore, lee-side
cyclogenesis will allow some easterly flow which looks to enhance
snow potential over the Palmer Divide where snow probabilities for
4 or more inches are around 10-20%.

Day 3...
The probability for heavy snowfall (4 inches of more) is less than
10 percent.


The probability for significant icing (0.25 inches or more) is
less than 10 percent Days 1-3.

Fracasso