The Weather Prediction Center

College Park, MD

Probabilistic Heavy Snow and Ice Discussion

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 PM EDT Mon Mar 18 2019

Valid 00Z Tue Mar 19 2019 - 00Z Fri Mar 22 2019

...California...Great Basin...Southern Rockies....
Days 1-3...

A shortwave diving through the Northern Plains tonight into
Tuesday will drive a cold front southward through the High Plains
and into the central Rockies in advance of a ridge of high
pressure. This will produce an enhanced temperature gradient and
subtly increased upslope flow to produce a few inches of snowfall
in the Colorado Rockies through Day 1. WPC probabilities are low
for 4 inches of snow, highest in the Sangre De Cristos near the NM

A more robust system will approach the Southern California coast
Wednesday as a deep upper trough cuts beneath an amplifying ridge
over western Canada. A significant moisture plume shifting onshore
beneath a jet max rotating beneath the trough will spread
precipitation from California, across the Great Basin, and into
the Central and Southern Rockies by Thursday. Forcing will be
intense in the favorable upslope regions of the Sierra Nevada on
Day 2, and then the Southern Wasatch and San Juans/Sangre De
Cristos on Day 3. Snow levels will gradually climb through the
period as the ridge strengthens to the north, becoming 5-6 kft in
the California, and as high as 8 kft in NM/CO by the end of the
forecast period. This will confine the highest snowfall to the
highest terrain of the mountain ranges, but WPC probabilities are
high for 12 inches in the Wasatch and San Juans on Day 3, and
moderate in the Sierra on Day 2. Elsewhere, probabilities for 4
inches are moderate across much of the terrain above 6000 ft from
the mountains of Nevada south and east into the White Mountains of
Arizona, the northern Wasatch, and the Colorado Rockies.

Day 3...

A shortwave digging through the Great Lakes Wednesday night will
produce a trough which shifts eastward through New England
Thursday. Increasing diffluence within the RRQ of a departing
100kt upper jet combined with PVA and height falls ahead of the
shortwave will produce snow in the terrain of New York and New
England on Day 3. Additionally, cold advection behind this feature
creates an environment favorable for Lake Effect snow downwind of
Erie and Ontario. The duration and intensity of forcing is modest,
so accumulations are expected to remain light, with WPC
probabilities for 4 inches exceeding 40 percent only in the Tug
Hill Plateau and Adirondacks of New York downwind of Lake Ontario.

The probability for significant (0.25 inches or more) freezing
rain is less than 10 percent all 3 days.


Last Updated: 422 PM EDT MON MAR 18 2019