Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 AM EST Fri Jan 08 2021

Valid 12Z Fri Jan 08 2021 - 12Z Mon Jan 11 2021


Day 1...
...Tennessee Valley to the Southern Appalachians...
The closed low currently over the TN Valley will shift east,
crossing the Carolinas this afternoon/evening. With energy
transferring to the surface low along the Carolina coast this
morning, continued heavy snow in the higher elevations in the
easterly flow north of this low is expected into this afternoon.
Light to moderate probabilities for 4 or more inches after 12Z are
on the eastern side to the crest of the Smokies, quickly dropping
off into southwest VA. Low to moderate probabilities for one or
more inches then spread east onto the Piedmont broadly along the
NC/VA border.

...Pacific Northwest...
A well-defined shortwave/upper jet positioned along the base of a
broader scale trough will track inland from the Pacific Northwest
coast this morning. A period of deep westerly flow, along with
favorable upper jet forcing, will support locally enhanced
precipitation, including mountain snows along the Cascades into
the Shasta-Siskiyou region, with the heaviest accumulations most
likely along the higher elevations of the central to southern
Oregon Cascades where Day 1 snow probabilities are low to moderate
for 6 or more additional inches starting at 12Z. A pronounced
ridge immediately following this trough will cut off Pacific
moisture, greatly limiting the heavy snow potential for terrain as
the trough crosses the Great Basin through tonight.

Days 2/3...
...Southern Rockies and Southern Plains to lower Mississippi
Valley...
The previously noted shortwave entering the Pacific Northwest this
morning will dig southeast across the Great Basin tonight and into
the Four Corners region on Saturday. As the system then shifts
southeast into the southern Rockies, increasing low level
southeasterly flow sourced from the Gulf of Mexico, along with
left-exit region jet forcing will support precipitation developing
by Saturday evening from the Panhandle region into the southern
Rockies. Precipitation is forecast to continue through the
overnight across portions of the Panhandle region and eastern New
Mexico, with cold air aloft sufficient for snow across the region.
00Z global guidance continues to depict a closed low developing
over New Mexico Saturday night that then tracks east across the
state through Sunday night. Dynamic cooling is expected to help
draw the rain-snow line farther southeast on Sunday, introducing
the potential for locally moderate snowfall accumulations into
portions of Northwest Texas, northern Louisiana, and southern
Arkansas by Sunday evening.  
Day 2.5 snow probabilities for 4 or more inches (most of which
will fall in 12 hours or less) are 50 to 70 percent from
east-central New Mexico arcing across the southern Texas Panhandle
to northwest Texas by Day 3. Low Day 3 probabilities for 2 or more
inches arc across north Texas to northern Louisiana.


For Days 1-3, the probability of icing of 0.1 inch or greater is
less than 10 percent.

Jackson