Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
420 AM EST Thu Feb 13 2020

Valid 12Z Thu Feb 13 2020 - 12Z Sun Feb 16 2020


Days 1-3...

...Pacific Northwest to the Northern Rockies...
A shortwave trough currently centered over the Gulf of Alaska and
the northeastern Pacific will drop southeast, moving across the
northwestern U.S. Thursday night into early Friday.  This system
is expected to bring several inches of snow to the higher
elevations of the Olympics and the Washington Cascades, with
lighter amounts farther south along the Oregon Cascades and east
into the northern Rockies. 

Persistent onshore flow with embedded mid-to-upper upper level
energy will support additional snow showers through Friday before
the next system arrives on Saturday, bringing the next round of
organized precipitation into the region.  This system is expected
to be wetter than the previous, with heavy mountain snows likely. 
Areas impacted will likely include the Cascades, Blue Mountains,
the northern and central Idaho and the western Wyoming ranges. 
For the 24-hr period ending 12Z Sun, WPC PWPF is indicating at
least a localized threat for accumulations of a foot or more
across these areas.

...Great Lakes/Northeast...
Mid-level energy lifting out of the base of a longwave trough
centered over the central U.S. will move quickly off to the
northeast Thursday morning.  Surface low pressure developing along
the northern Mid Atlantic coast is expected to move quickly
offshore.  Light to moderate to snows will continue to move east
across Upstate New York and northern New England, with an
additional inch or two possible after daybreak.  An upstream
shortwave trough will bring additional light snows and much colder
air across the Great Lakes into the Northeast later in the day on
Thursday, with northwesterly flow behind the associated cold front
supporting lake enhanced showers in the lee of the eastern Great
Lakes.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira