Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
431 PM EDT Fri Apr 05 2019

Valid 00Z Sat Apr 06 2019 - 00Z Tue Apr 09 2019


...Pacific Northwest to the Northern Rockies...

A series of shortwaves and their associated frontal bands are
forecast to move across the region, including a system positioned
along the leading edge of a strong upper jet and long fetch of
Pacific moisture that is expected to move inland on Sunday.  On
average, snow levels are expected to remain at or above 4000 ft,
with the Olympics, northern Cascades and the Sawtooth of central
Idaho expected to see some of the heavier accumulations over the
period.  For the three day period ending 00Z Tue, WPC guidance
indicates a 50 percent chance or greater for total accumulations
of 12 inches or more across portions of those areas.

...Great Lakes to the Northeast...

Strong low level theta-e advection ahead of an amplifying
shortwave emanating from the West is expected to support
widespread precipitation developing across the Upper Midwest-Great
Lakes on Sunday.  Confluent flow downstream, supporting cold high
pressure will produce wintry precipitation mainly north of the
international border through Sunday.  Then as the system moves
farther east into southern Ontario, precipitation extending east
out along the associated warm front is expected to fall as frozen
across portions of northern New England Sunday night into Monday. 
Precipitation may continue as frozen for portions of the region
through the end of th period as a developing low over the Gulf of
Maine helps to lock in the cold air.  For the 24-hr period ending
00Z Tuesday, WPC guidance shows a Slight Risk for accumulations of
8-inches or more across northern Maine with a Slight Risk for ice
accumulations of 0.25 inch or more across portions of northern
Vermont to northern Maine.

Pereira