Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
325 PM EDT Tue May 02 2023

Valid 00Z Wed May 03 2023 - 00Z Sat May 06 2023


...Central Appalachians... 
Day 1... 
As an anomalously deep mid-to-upper level low settles southeast
from the Great Lakes, late-season snow showers are expected to
continue through the overnight into Wednesday across portions of
the central Appalachians, with additional accumulations possible
in parts of the West Virginia mountains.  A series of shortwaves
digging south of the low will support periods of greater ascent as
the air column remains sufficient cold enough for snow across the
higher terrain.  WPC guidance indicates that additional
accumulations of 4 inches or more are likely over West Virginia's
Allegheny Mountains tonight and during day on Wednesday,
especially for areas above 2000 ft.  By Wednesday night, showers
are expected to wane as the upper low continues to move east --
reaching the eastern Atlantic Thursday morning.
 
...California through the Great Basin... 
Days 1-3... 
Encouraged south by a blocking ridge to its east, another
anomalously deep mid-to-upper level low is forecast to bring cool
and unsettled weather across California into Thursday before
beginning to lift northeast as an open wave across the Great Basin
Thursday night into Friday.  While not an unusually moist system,
the notable synoptic-scale ascent associated with this system will
likely be sufficient for at least widespread light precipitation
totals, with orographically focused heavier amounts across
California.  Locally heavy snow accumulations are possible along
the Sierra and the Southern California Transverse Ranges, where
snow levels are expected to generally fluctuate between 4000-5000
ft.  As the low opens up and lifts northeast, generally light
amounts are expected to spread across the Nevada mountains into
the northern Rockies Thursday night and Friday.
 
 
The probability of significant icing greater than 0.25" is less
than 10 percent. 
 
Pereira