Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 PM EST Sun Dec 02 2018

Valid 00Z Mon Dec 03 2018 - 00Z Thu Dec 06 2018

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

Potent mid-level shortwave and accompanying strong jet maximum
will rotate through the west coast longwave trough and into the
Southwest tonight. By Monday afternoon, the jet energy providing
ascent through diffluence will outrun the best moisture, so
snowfall is expected to be confined to a stripe from the mountains
of Utah southwest into the Panhandles of Texas and Oklahoma. The
progressive nature of this system and gradual reduction in
mid-level RH suggests snowfall accumulations will be modest, and
WPC probabilities for 4 inches are moderate only in the high
terrain of Colorado. Lesser amounts are likely elsewhere.

On Day 2 into Day 3, a closed mid-level low and associated surface
reflection will drop southward just offshore the coast of
California. Moisture will stream onshore ahead of this feature on
increasing low and mid level south/southwest winds which will
impinge upon the Sierras of California, especially by Wednesday.
Heavy snow is likely above 8000 feet, and WPC probabilities are
high for 8 inches in the central and southern Sierra Nevada range.
Also during day 3, mid-level moisture will stream eastward into NV
and UT along a 700mb confluent axis. This may produce light snows
into the terrain of these states as well, but WPC probabilities
are low for 4 inches at this time.

... Great Lakes ...

Low pressure moving northeast from the Great Lakes towards New
Brunswick, Canada, will drag a cold front across the Upper Midwest
and New England through today. Moisture associated with this
feature is progressive, but trajectories behind the front will
become aligned along the Lakes to produce light lake effect snow.
The heaviest snow is likely south of Lake Superior and Lake
Michigan where winds will become uniformly from the north to
produce unidirectional shear, with lesser snow expected downwind
of Lake Erie as winds begins to shift. Instability is limited and
equilibrium levels are only 5-6 kft, so accumulations are likely
to remain low. WPC probabilities for 4 inches are moderate in the
U.P. of Michigan, but otherwise only 1-3" of snow is forecast
downwind of the lakes.


The probability of significant icing (0.25 inches or more) is less
than 10 percent.

Weiss