Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 AM EST Mon Jan 11 2021

Valid 12Z Mon Jan 11 2021 - 12Z Thu Jan 14 2021

...Central Mississippi into northern Alabama...
Day 1...

Low pressure currently centered over the ArkLaTex early this
morning will continue shifting east-northeast over central MS to
northern AL into this afternoon. The locally moderate snow being
produced on the northern end of the precip shield (over northern
LA into central MS as of 08Z) can be expected to continue as it
shifts east. Day 1 snow probabilities are moderate for a inch or
more after 12Z in east-central MS with some low probabilities in
the Great Smokies tonight. Snow rates are expected to quickly
decrease this afternoon as the system shears out and outpaces the
cold air centered over the southern Plains as it crosses from
northern AL into the Tennessee valley.


...Pacific Northwest and Northern Rockies...
Days 1-3...

An atmospheric river event is set to unfold, with heavy
precipitation likely to develop across across western Washington
and Oregon beginning later this morning and continuing through
Tuesday into early Wednesday. High snow levels (rising to around
5000ft today then up to 7000ft tonight before decreasing to around
4000ft on Wednesday as precip lightens) are expected to confine
the threat for heavy snow to the higher elevations of the Olympics
and northern Cascades -- where several feet are expected by
Wednesday evening. Through late Tuesday there is some threat for
locally heavy snow accumulations across the higher elevations of
the northeastern Washington and northeastern Oregon mountains into
the Rockies. However, the potential is expected to increase on
Wednesday as a well-defined shortwave trough, drives a strong cold
front into the region.

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

Jackson