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

Valid 00Z Fri Apr 05 2019 - 00Z Mon Apr 08 2019


...Pacific Northwest and Northern California to the Northern and
Central Rockies....

A pair of upper level shortwaves and their associated frontal
bands are expected to impact the region Thursday night into
Friday, including mountain snows from the Olympics, Cascades and
Sierra to the northern Rockies.  Overall, models have trended
warmer over the past day, with the latest guidance showing little
potential for heavy accumulations apart from some of the higher
peaks of the southern Cascades, northern Sierra and Sawtooth
through Day 1 (ending 00Z Saturday).

Shortwave energy embedded within diffluent flow aloft will
continue to support showers across the region into Saturday. 
Shortwave ridging may provide a brief break before the leading
edge of a strong Pacific jet and associated frontal band begin to
move into the Pacific Northwest Saturday night.  Falling snow
levels behind the front may support some heavy snow accumulations
across the Olympics and northern Cascades, with WPC Day 3
probabilities (ending 00Z Monday) indicating a Slight Risk or
greater for accumulations of 8-inches for elevations above 4000
ft.

...Great Lakes/Northeast...

Low level theta-e advection interacting with retreating high
pressure is expected to support a period of mixed precipitation
across portions of the region Thursday night into Friday.  While
widespread heavy snow or significant ice accumulations are not
expected, WPC guidance shows greater than 50 percent probabilities
for measurable ice across portions of northern lower Michigan as
well as the Southern Tier of New York and northern Pennsylvania
eastward into he Poconos and Catskill Mountain regions.

...Northern Minnesota...

Strong warm advection ahead of a shortwave trough emanating from
the West is expected to support increasing precipitation chances
across the Upper Midwest Sunday morning.  Confluent downstream
flow will support high pressure and a chance for mixed
precipitation across northern Minnesota, with WPC probabilities
indicating a Slight Risk for ice accumulations of 0.25 inch or
more over the Arrowhead on Day 3 (ending 00Z Monday).

Pereira