Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
442 AM EDT Tue Oct 27 2020

Valid 12Z Tue Oct 27 2020 - 12Z Fri Oct 30 2020

...Southern Rockies and Plains...
A deep, upper low closing off over the southwestern U.S. is
expected to move east along the U.S.-Mexico border toward Far West
Texas on Tuesday.  Increasing lift ahead of the low, along with an
influx of deeper moisture, is expected to support another round of
organized heavier precipitation across portions of western and
central Texas, and Oklahoma early Tuesday.  With shallow, low
level cold air remaining in place, this will likely result in
another round of wintry, mixed precipitation, especially from the
Texas Hill Country northward into western and central Oklahoma. 
Some areas already impacted by significant ice accumulations
during the first round of wintry weather are likely to see
additional freezing rains, with impactful accumulations on
Tuesday.  Heaviest ice accumulations are forecast to center over
western Oklahoma, where the latest WPC PWPF shows widespread
probabilities of 50 percent or greater for ice accumulations of
0.25-inch or more. 

Meanwhile, well to the west and within the deeper cold air,
additional snows are likely from the moutains of central New
Mexico eastward into the Texas Panhandle.  As the upper low moves
east, strong lift developing along the left-exit region of an
upper jet streak will support heavier amounts forming across
eastern New Mexico into the Panhandle.  With the air column
remaining cold enough to support snow, additional impactful
accumulations are expected across portions of eastern New Mexico
into the Texas Panhandle on Tuesday.  As the associated low-to-mid
level center begins to move out across western and central Texas
Tuesday night into Wednesday, easterly to northeasterly flow on
the back side of the center is expected to keep enough cold air in
place for additional snow accumulations across northeastern New
Mexico, southeastern Colorado and the western Pandhandle region. 
The threat for winter weather is expected to finally come to an
end as the system begins to accelerate rapidly east by early
Thursday.

...Northeast...
As it begins to interact with the northern stream, the upper low
moving out of the southern Plains by early Thursday is forecast to
accelerate eastward, reaching the Mid-Atlantic states by early
Friday.  Models have shown some potential for accumulating snows
developing across portions of Upstate New York and northern New
England as cold high pressure over Canada and low-to-mid level
frontogensis interact with moisture spreading north. 
Unfortunately, models have shown a fair amount of spread regarding
the degree of phasing and the timing of this system, resulting in
a good deal of uncertainty regarding the placement and magnitude
of any accumulating snows.  Latest trends however, including those
shown by the European and UKMET are pointing toward a more
suppressed solution, with lighter accumulations across northern
New York and New England.

Pereira