Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EST Tue Nov 27 2018

Valid 12Z Tue Nov 27 2018 - 12Z Fri Nov 30 2018


...Great Lakes/Northeast...

Low along the Northeast coast will continue to deepen and track to
the north into New England on Tuesday.  Strong upper forcing and
low to mid level frontogenesis will help support precipitation
across the Northeast, with additional heavy snow accumulations
possible across northern New York and the mountains of northern
New England.  Snows are expected to wane as the low redevelops and
moves by late Wednesday. 

Meanwhile, strong northwesterly flow/cold air advection will
support lake effect snow showers, producing locally heavy
accumulations Tuesday into Wednesday, especially in the lee of
Lake Erie where amounts of a foot or more are possible.  By early
Thursday, showers are expected to diminish as a shortwave ridge
moves across the lakes.

...Western U.S....

Models are showing a brief period of zonal flow across the West as
the upper trough currently off of the Pacific Northwest coast
moves inland later today, breaking down the ridge centered over
the Rockies.  Snow levels will remain relatively high, however low
amplitude energy may help support some locally heavy high
elevation snows over the Cascades into the northern Rockies
Tuesday into early Wednesday.  By early Thursday the flow across
the west is expected to amplify once again as a well-defined
shortwave and strong upper jet move into California.  Snow levels
are forecast to fall considerably as the system moves inland, with
heavy snow accumulations becoming likely along the Sierra.  WPC
probabilities show a Moderate Risk for accumulations of a foot or
more for elevations above 7000 ft on Day 2 (ending 12z Thu),
dropping to 6000 ft on Day 3 (ending 12z Fri), with two day totals
possibly exceeding 30 inches in some locations.

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

Pereira