Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EST Wed Feb 19 2020

Valid 12Z Wed Feb 19 2020 - 12Z Sat Feb 22 2020


Day 1...

...Central Plains and Rockies...
Deepening moisture, supported by southerly inflow will support
light to moderate snows along a low-level boundary settling south
across Nebraska Wednesday morning.  While heavy amounts are not
expected, WPC PWPF indicates that snowfall accumulations of two
inches or more are likely from northeastern to southwestern
Nebraska.  By late Wednesday afternoon, models show snows
beginning to develop farther south near a low level wave dropping
south through eastern Colorado.  This feature will help support
light accumulations across western Kansas into the plains of
southeastern Colorado, with locally heavier amounts in the upslope
regions of the adjacent mountains.  WPC PWPF indicates some
locally high probabilities for snowfall accumulations exceeding
6-inches along the Sangre de Cristo mountains for late Wednesday
into early Thursday.

...Central New York...
A secondary shot of colder air. along with northwesterly flow from
the Upper Great Lakes across Lake Ontario, will support lake
effect snow showers with locally heavy accumulations possible
southeast of Lake Ontario late Wednesday into early Thursday.

Day 2...

...Southern Appalachians and Mid Atlantic...
A steady flow of southern stream energy and moisture, along with
favorable upper jet forcing will support widespread precipitation
north of a frontal boundary extending across the northern Gulf of
Mexico and Florida on Thursday.  As a positively-tilted northern
stream trough moves into the Ohio and Tennessee valleys, there is
still a fair amount of uncertainty regarding an area of low
pressure expected to develop along the front off of the Southeast
coast and its potential impacts across North Carolina and southern
Virginia on Thursday.  The NAM, and to a lesser-extent the GFS,
remain at odds with the non-NCEP deterministic guidance.  The NAM
remains more bullish than the remaining deterministic guidance --
indicating a more amplified solution, in-turn directing more
moisture into the cold air north of the front, with moderate to
heavy snows covering a large portion of northern North Carolina
and southern Virginia. WPC preferred a solution more similar to
the ECMWF, but a bit heavier given its most recent trends toward a
solution more similar to the GFS across northeastern North
Carolina and southeastern Virginia. 

Day 3...

...Sierra...
An upper low developing and dropping south along the northern
California coast Thursday into Friday is expected to turn
southeast into southern California by late Friday.  Despite strong
upper dynamics and onshore flow, models do not indicate a lot of
moisture with this system; so overall expect precipitation amounts
to be light, with only a few inches of snow expected along the
central to southern Sierra by early Saturday.

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

Pereira