Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
429 PM EDT Tue Oct 19 2021

Valid 00Z Wed Oct 20 2021 - 00Z Sat Oct 23 2021

...Eastern Wyoming, western South Dakota, and northwestern
Nebraska...
Day 1...
A low pressure system, with a upper low currently centered over
northwest CO with a surface cyclone along the northern CO/KS
border will shift east-northeast over the north-central Plains
through Wednesday morning. The left-exit region of the jet around
the upper low will continue to aid lift of Gulf-sourced moisture
and support widespread precipitation, including areas of heavy
snow over the north Laramie Range and the Black Hills tonight
where Day 1 snow probabilities for 4 or more inches are moderate.

In addition to the strong upper forcing, easterly to northeasterly
flow on the north side of the surface low is upslope over western
SD and northwestern Neb where good low-to-mid level frontogenesis
will lead to mesoscale bands of accumulating snow tonight that
overcome marginal thermal conditions. Day 1 WPC snow probabilities
for 2 or more inches are 30 to 50 percent in at least a few
stripes of areas including the Pine Ridge area of northwest Neb
and areas east/southeast of the Black Hills over the western half
of SD.


...Cascades...
Snow levels remain 6000ft or higher through heavy precipitation
spreading inland both tonight and Thursday night.


For Days 1-3, the probability of significant icing (0.25 inch or
more) is less than 10 percent.

Jackson