Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EST Sun Jan 10 2021

Valid 12Z Sun Jan 10 2021 - 12Z Wed Jan 13 2021


...Southern Plains to the Lower Mississippi Valley...
Day 1...

A low pressure system, currently centered over southern NM and far
western TX will shift east across west TX today and North TX
tonight before weakening as it crosses the Mid-South Monday.
Left-exit region upper jet forcing is supporting large-scale lift
across the southern High Plains of eastern NM and the TX Panhandle
this morning. This lift along with deep moisture, supported by low
level southeasterly flow across Texas is producing organized
heavier snow rates across eastern NM, the TX Panhandle south to
Midland, TX/the Permian Basin. With thermal profiles maintaining
snow from the onset across the Concho Valley and NW TX, sustained
lift interacting with ample moisture is expected to support
several hours of moderate to locally heavy snowfall across this
region and east to the I-35 corridor south of DFW into this
afternoon.
Then, this evening as surface low pressure refocuses on the TX
coast, a secondary area of moderate to locally heavy snow is
expected to develop in east TX and across northern LA to the MS
Delta tonight. Marginal boundary layer temperatures tonight in
this area may limit notable accumulations on the ground except
where dynamics are best with heavier rates repeating in bands
allowing 2 to perhaps 5 inches accumulating near the TX/LA border
south of I-20. Day 1 snow probabilities which begin at 12Z are
moderately high for 6 or more inches across Northwest TX with 20
to 30 percent probabilities for 4 or more inches extending from
the southern TX Panhandle all the way east across TX into northern
LA. 
The system then weakens/fills and outpaces cold air limiting heavy
snow to the Day 1 period with some notable light snow up to an
inch Monday morning in northern MS.


...Northwest...
Days 2/3...

A potent shortwave trough rounding a Gulf of Alaska low pushes
into BC Monday night with an Atmospheric River pushing into the WA
coast. Snow levels generally rise from 4500ft to 6000ft in the
Olympics and WA Cascades Monday night with particularly heavy snow
above these levels. Day 2 snow probabilities are moderately high
for 8 or more inches in the northern WA Cascades. Zonal flow on
Tuesday focuses the Atmospheric River into the OR/CA border into
Wednesday with very high snow levels (around 8000ft) in the very
moist air. Deep Pacific moisture will make it past the Cascades
with Day 3 snow probabilities for 8 or more inches likely for the
Blue Mtns of OR and the Bitterroots on the ID/MT border and high
probabilities for the northern WA Cascades.
  

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

Jackson