Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
338 AM EST Mon Nov 19 2018

Valid 12Z Mon Nov 19 2018 - 12Z Thu Nov 22 2018


...Great Lakes/Northeast...

Days 1-3...
Two shortwave troughs will round the mean trough over eastern
Canada and cross the northeastern CONUS through Wednesday night.
The first shortwave trough is pushing southeast from MN this
morning with generally light snow expected until a coastal low
develops over the Gulf of Maine with the trowal over coastal Maine
where there is a 30 to 50 percent chance of four inches.

A trailing shortwave is forecast to dive southeast from Canada
across the Great Lakes on Wednesday. This will bring a round of
light snows along with the wave to northern and western New York
and Maine before it phases into the stronger low over eastern
Canada. Lake effect snow showers in low level westerly winds and
cold air advection increase across lakes Erie and Ontario in the
wake of this low on Wednesday. 


...West Coast...

Day 3...
A deep trough and surface cold front will push across the west
coast Wednesday night.  A subtropical Pacific fetch into this
system will bring widespread precipitation north from the central
California Coast beginning late Tuesday night that spreads over
the Sierra Nevada/Cascades and into the Great Basin by late
Wednesday night. 1.5 to 2 inches of QPF in preferred upslope areas
of CA will result in heavy snow in higher terrain. NBM snow levels
are generally 5 to 7 kft through this event in CA and 4 to 5 kft
in WA. The central and northern Sierra Nevada are expected to
receive the highest snow totals with 50 to 70 percent chance of
eight inches through Wednesday night. Another cold front will
approach Thursday and make for an active pattern out west through
the rest of the week.


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

Jackson