Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Sat Apr 06 2019

Valid 12Z Sat Apr 06 2019 - 12Z Tue Apr 09 2019


...Pacific Northwest to the Northern Rockies...
Days 1-3...

The strongest shortwave trough of a series rounding a low off BC
will push across the WA coast today. At atmospheric river comes
ashore over the Pac NW coast tonight through Sunday night before
being shunted south to northern CA Monday. Snow elevation will be
3000 to 4000ft over WA ahead of the AR. A strong baroclinic zone
allows very high snow elevation of 7000 to 8000ft south of the AR
axis and generally around 4000ft still over WA. The Olympics,
northern Cascades and the Sawtooth of central Idaho expected to
see the greatest accumulations in Days 1/2. For the two day period
ending 12Z Mon, WPC guidance moderate chances for 18 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 Canadian Prairies Sunday will push
across New England Monday. Confluent flow downstream, supporting
surface high pressure of 1024mb will allow wintry over interior
New England Sunday night through Monday. Then as the system moves
farther east into southern Ontario, precipitation extending east
out along the associated warm front is expected to fall as snow
across portions of northern New England Sunday night into Monday.
Precipitation may continue as frozen for portions of the region
through the end of the period as a developing low over the Gulf of
Maine helps to lock in the cold air. For the 24-hr period ending
12Z Tuesday, WPC guidance shows moderate probabilities of 8-inches
or more across northern Maine with a moderately low probabilities
for a quarter inch of ice across portions of northern Vermont to
northern Maine.

Jackson