Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Thu Apr 04 2019

Valid 12Z Thu Apr 04 2019 - 12Z Sun Apr 07 2019


...Western U.S....
Days 1-3...

A series of shortwave troughs round a Gulf of Alaska low and push
into the West Coast starting early this evening and continuing
through the forecast period and continuing into next week. Snow
elevations are high initially 6000 to 7000ft range among the
widespread precipitation with heavy snow for the higher for the OR
and CA Cascades on Day 1 where moderate probabilities for six
inches are present over the volcanoes of northern CA.

The second trough is more robust with both the upper level wave
and surface front that is forecast to move inland on Friday. The
heavier precipitation and snow elevations lowering to 5000 to
6000ft raises the threat for another round of 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. The highest elevations have moderate
probabilities for six inches as the system shifts east on Days
2/3.


...Great Lakes/Northeast...
Days 1-2...

Warm advection precipitation associated with a weak shortwave
shifting east from the Great Plains today is expected to begin as
a period of mixed wintry precipitation for northern MI tonight
into Friday. Light snow is expected late tonight over  northern WI
and The UP, while farther south and east a couple pockets of
freezing rain in northern lower MI into parts of northern PA.

By Friday night, the wintry mix will shift northeast across
interior New England where 1035mb surface high pressure will have
been centered Friday morning. The overrunning flow will cause a
swath of wintry mix south of snow with Day 2 WPC probabilities low
for snow of 4 inches or greater across northern Maine and New
Hampshire. Also on Day 2 are moderate probabilities for a tenth
inch of ice over the Catskills, Adirondacks, and Green/White
Mountains.

Jackson