Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
404 PM EDT Wed Apr 03 2019

Valid 00Z Thu Apr 04 2019 - 00Z Sun Apr 07 2019


...Western U.S....

Ridging over the West on Thursday is forecast to give way to a
series of shortwave troughs, producing widespread precipitation
including locally heavy high elevation snow accumulations from the
Pacific Northwest and northern California to the northern Rockies.
 Models show the initial shortwave weakening as it moves inland
Thursday night, producing generally light snows from the northern
Sierra and Cascades to the northern Rockies late Thursday into
early Friday.  This will be followed by a more robust upper level
wave and surface front that is forecast to move inland on Friday
-- producing heavier precipitation and raising the threat for
locally heavy snows across portions of the southern Cascades to
the northern Sierra.  The front will push through the Pacific
Northwest Friday evening, which along with post frontal onshore
flow will contribute to some locally heavy snow accumulations
across the northern Cascades and Olympics.  As the front continues
to move east Friday night into Saturday, models show high
elevation snows with generally light accumulations spreading from
the Intermountain West into the northern and central Rockies.

...Great Lakes/Northeast...

As it interacts with a retreating high, warm advection
precipitation associated with a weak wave moving out of the
Midwest is expected to begin as a period of mixed wintry
precipitation across the Great Lakes into the Northeast Thursday
night into Friday.  While the models differ on the details, with
the NAM begin the coldest, most agree on at least some minor ice
accumulations from portions of northern Wisconsin and Michigan
eastward into parts of northern Pennsylvania and Upstate New York.

By Friday night, wintry precipitation will shift farther northeast
into northern New England, with the WPC probabilities showing a
low-end chance for snow accumulations of 4-inches or greater
across northern Maine and New Hampshire.

Pereira