Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
419 PM EST Fri Mar 05 2021

Valid 00Z Sat Mar 06 2021 - 00Z Tue Mar 09 2021


...Pacific Northwest/California to the Northern Rockies...
Days 1-2...
Ongoing precipitation associated with a frontal band moving inland
across the Pacific Northwest and Northern California is expected
to continue through the evening, with additional mountain snows
likely from the Olympics and Cascades to the northern Sierra. 
While accumulations are expected to be light across most areas, a
well-defined shortwave moving through the base of the broader
scale trough is expected to amplify near the Northern California
coast overnight.  This will likely support some heavier
accumulations, especially across the mountains of northwestern
California into the southern Cascades.  WPC PWPF suggests
widespread additional accumulations of 4-8 inches are likely
across this region during the evening and overnight hours.  Snows
are expected to quickly diminish across this area as the shortwave
lifts northeast of the region on Saturday. 

Shortwave energy rotating out ahead of a closed low centered west
of British Columbia will drive another front into the Northwest
Sunday morning, with heavy snow accumulations likely over the
Olympics.  The potential for organized heavy amounts is expected
to diminish as the front moves east and weakens on Sunday.

...Eastern Great Lakes...
Days 1-2...
Deep northwesterly flow with embedded energy aloft will support
multi-band lake effect snow showers south of Lake Ontario and
eastern Lake Erie Friday night into Saturday.  While widespread
heavy amounts are not expected, at least a couple of inches of
snow are likely, especially north of and along the Finger Lakes
region.  Snows will likely diminish as a surface high pressure
shifts east into the region by late Saturday.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira