Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 PM EST Fri Feb 15 2019

Valid 00Z Sat Feb 16 2019 - 00Z Tue Feb 19 2019


...Western U.S....
Days 1-3...

The West will remain active, but in a slowly decreasing sense
through the forecast period into early next week. A large
positively tilted upper trough will be periodically reinforced by
shortwaves digging southward along the Pacific Coast, while at the
same time shedding energy into the fast flow to the east. Through
the weekend and into early next week, the main focus for
precipitation will be shunted southward as the Pacific Jet gets
suppressed towards Baja and into the Southwest. This will bring a
decrease in snowfall north of 40N, but an increase to the south,
with the Mogollon Rim favored for heavy snow on Monday. Over the
three day period, heavy snow is likely across all the terrain,
with snow levels falling to as low as 500 ft or less north of 40N
away from the coast, and as low as 3000-4000 ft near the Mexican
border Monday. Snow amounts will likely exceed 2 feet in the
Sierra as well as the Siskiyous and Shasta/Trinity ranges in
California, with 1-2 ft across the Mogollon Rim, San Juans, and
northern Rockies. Amounts will be lighter elsewhere, but with snow
levels falling, even the lower terrain of the mountains around San
Francisco and some of the lower elevations of Nevada and Arizona
may see a few inches of snowfall by early next week.


...Northern and Central Plains...
Days 1-2...

A shortwave shedding from the upper low across the West will push
eastward into the Plains and close off as it interacts with a
northern stream impulse (but doesn't phase). Height falls and
300mb diffluence atop a jet streak to the south will create a
swath of snowfall from eastern MT southeast into the central
Plains through Sunday. This feature will move quickly to the east
as it opens late on Sunday, but a brief period of coincident 700mb
deformation and mid-level divergence will produce moderate snows,
focused from SD into IA, where WPC probabilities are moderate for
6 inches. Elsewhere WPC probabilities are high for 4 inches from
fast eastern MT into southwest WI.


...Mid-Atlantic and Ohio Valley...
Day 1...

A wave of low pressure beneath a weak shortwave will move east
tonight into Saturday bringing a stripe of light snow.
Temperatures will be marginal as the cold air comes in primarily
behind this system, but a brief overlap of cold temperatures and
modest ascent due to height falls and jet level diffluence will
produce snow, generally 1-2 inches, from western KY eastward into
central VA. Some slightly higher amounts are possible in the
terrain of WV/VA where WPC probabilities are 20-30% for 4 inches.
South of this stripe of snow, a small area of freezing rain is
likely across primarily southern KY. Here, WPC probabilities are
moderate for 0.1 inches just east of the Bootheel of MO, with
lesser amounts further east.


...Northeast...
Day 3...

A shortwave opening from the Great Lakes will shear off to the
northeast beneath a potent (180+ kt) 300mb jet will spawn weak
cyclogenesis moving off the coast. Strong synoptic ascent within
the LFQ of this jet will combine with weak lift along the 700mb
trough axis to produce a quick shot of snow Sunday night into
Monday. 1000-500mb RH dries quickly into Monday so total snowfall
is expected to be light, and WPC probabilities are less than 40
percent for the northeast, highest in the Adirondacks of New York
with lesser amounts possible all the way to the coast of Maine.


Weiss