Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
347 PM EST Sun Nov 18 2018

Valid 00Z Mon Nov 19 2018 - 00Z Thu Nov 22 2018


Days 1-3...

...Great Lakes/Northeast...

A broad upper level trough will shift gradually east from the
central into the eastern U.S. this period.  A shortwave trough
embedded within the broader scale trough will drop southeast from
central Canada into the upper Great Lakes region on Monday. 
Models continue to show synoptically driven light snow, followed
by lake effect showers, with some low-end probabilities for snow
accumulations of 4-inches or more in the lees of Lake Superior and
northern Lake Michigan during the Day 1 period (ending 00 UTC
Tuesday).  The shortwave trough will continue to swing east Monday
night into Tuesday, with a surface low developing and tracking
east from the Mid-Atlantic region.  Low to mid level frontogenesis
is expected to help support the development of light to moderate
snows north of the low from northeast Pennsylvania into portions
of Upstate NY and central New England.  WPC probabilities reflect
the trend toward heavier snow accumulations across portions of the
region, with amounts of 4-inches or more becoming more likely
during the Day 2 period (ending 00 UTC Wednesday), especially
across some of the higher terrain.  The surface low will continue
to strengthen and track to the northeast along the New England
coast into Atlantic Canada Tuesday night.  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, followed by lake effect
snow showers as low level westerly winds and cold air advection
increase across lakes Erie and Ontario on Wednesday. 

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

Pereira