Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 PM EST Tue Jan 07 2020

Valid 00Z Wed Jan 08 2020 - 00Z Sat Jan 11 2020


Days 1-3...

...Western U.S....
An active pattern is expected to continue across the West as a
series of shortwave troughs move across the region.  The initial
shortwave and associated frontal boundary are forecast to move
through the Northwest into the northern Rockies, bringing
organized precipitation across the region Tuesday evening into the
overnight.  Onshore flow in its wake and ahead of the next system
will continue to support showers across the region through
Wednesday.  Areas impacted by the heaviest amounts late Tuesday
into Wednesday will likely include portions of the Cascades and
northern Rockies.

Models show a compact upper level shortwave diving southeast into
southwestern Oregon and northern California Wednesday night into
Thursday morning. This is expected to produce some moderate to
possibly locally heavy snows along the southern Cascades into the
mountains of northwestern California and the northern Sierra.

As this system dives into the Southwest and an upper ridge shifts
across the West, a brief period of drier weather is expected to
follow Thursday night into early Friday.  However, wet weather is
forecast to return to the Northwest on Friday as the next upper
level shortwave moves inland -- bringing another round of heavy
snows for the Olympics and northern Cascades.


...Great Lakes/Northeast...
The system currently impacting the Mid Atlantic is forecast track
east-northeast from the northern Mid Atlantic coast Wednesday
evening, tracking south of Long Island and southeastern New
England overnight.  This system is expected to spread a few inches
of snow across eastern Long Island and southeastern New England
Tuesday evening, before brushing the Maine the coast with a few
inches as well Wednesday morning. 

Meanwhile, a strong cold front associated with an amplifying upper
trough is forecast to move from the upper to the lower Great Lakes
overnight.  Northwesterly flow and cold air advection across the
upper lakes will support lake effect snow showers, with several
inches possible along the favored locations along the U.P. of
Michigan before snows diminish as high pressure moves into the
region Wednesday afternoon.  The front is expected to move east of
the lower lakes Wednesday morning, with westerly winds becoming
more northwesterly by the end of the day.  Several inches of snow
are possible across the western Southern Tier and Tug Hill regions
of New York.

High pressure will drift across the Northeast on Thursday,
supporting mostly dry weather across the region.  Warm advection
precipitation spreading into the region may begin as a brief
period of freezing rain across portions of Pennsylvania and the
Northeast on Friday.  However, with high pressure moving offshore,
most areas are expected to quickly change over to rain.

The probability of significant icing (0.25 inch or greater) is
less than 10 percent.

Pereira