Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
427 PM EST Thu Feb 07 2019

Valid 00Z Fri Feb 08 2019 - 00Z Mon Feb 11 2019


...Western U.S....

A pair of systems impacting the western U.S. are expected to
produce widespread snows across the Pacific Northwest and Northern
California, including lowland snows over western Washington and
Oregon as well as the North Coast of California.

A compact upper low off of the Pacific Northwest coast will
continue to drop southeast, moving into Northern California Friday
evening.  This system will bring some significant snows to the
Sierra as it weakens and pivots east across California Friday
night into Saturday.

Meanwhile, an anomalously deep upper low is forecast develop over
southern British Columbia and drop south along the Pacific
Northwest coast Friday night into Saturday.  The GFS shows 500mb
heights more than 2 standard deviations below normal across much
of western Washington and Oregon on Saturday.  This will support
significant snow accumulations for portions of western Washington,
including the lowland areas.  As the low continues to drop south,
snows are expected to extend south along the coastal ranges along
the North Coast of California on Saturday, with snow levels
dropping to as low as 500ft by Sunday morning.  Models show the
low transitioning to an open wave and moving east across the
Northwest and Northern California on Sunday.  Shortwave energy
moving through the base of the associated trough will enhance lift
along the trailing baroclinic zone, supporting additional heavy
amounts along the Sierra.  Two-day totals will likely exceed two
feet for portions of the northern Sierra.  As the remnant trough
moves east, expect lighter accumulations across northern Nevada
into the northern Rockies.

...Upper Great Lakes and Northern New England...

The system now entering the Great Lakes will continue to lift
quickly to the northeast, tracking north of the lakes into eastern
Ontario this evening.  On the backside of this departing system,
some additional light to moderate amounts can be expected during
the evening hours across northern Michigan.  In the warm advection
pattern well to the east, high pressure over the Canadian
Maritimes and weak low pressure to the south will help maintain a
cold air wedge, supporting a period of freezing rain across
portions of interior Maine Thursday night into Friday morning.

Pereira