Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 AM EST Thu Jan 16 2020

Valid 12Z Thu Jan 16 2020 - 12Z Sun Jan 19 2020


Day 1...

...Western U.S....
A mid-to-upper level shortwave moving south of a low centered west
of British Columbia will continue to amplify as it swings east
across California on Thursday.  This will drive a strong cold
front southeast from Northern through Central California.  Strong
onshore flow in addition to favorable upper forcing will support
heavy precipitation from the coastal ranges of northwestern
California to the Sierra.  WPC PWPF continues to show that
accumulations of a foot or more are likely along a large extent of
the Sierra before snows diminish late Thursday into early Friday.

...Southern High Plains to the Central Plains the Lower Missouri
Valley...
As the trough entering California on Thursday continues to move
east, mid-to-upper level southwesterly flow is forecast to
increase from the southern High Plains into central Plains
Thursday night into early Friday.  Mid level energy and favorable
upper jet forcing interacting with southeasterly low level flow
will support precipitation spreading northeast across the region. 
Closer to the surface, northeasterly to easterly winds will help
keep cold in place -- supporting freezing rain with accumulating
ice likely from the Texas Panhandle to central Kansas late
Thursday into the overnight. 

...Northeast...
As a broad upper trough sliding east across the Great Lakes and
Northeast begins to amplify, surface low pressure will begin to
strengthen as it moves from New England into the Gulf of Maine on
Thursday.  Low-to-mid level frontogenesis north of the low may
produce a period of moderate to heavy snowfall along the coast of
Maine before the system moves south of Nova Scotia Thursday
evening.  Strengthening northwesterly flow with embedded energy
aloft will support lake effect snow showers with locally heavy
accumulations possible downwind of the lakes and into the central
Appalachians.

Day 2...

...Midwest...
Low-to-mid level frontogenesis lifting northeast ahead of an
approaching upper level shortwave will support precipitation
spreading northeast from the central Plains, Ozark region and mid
Mississippi valley Friday morning, before reaching into the Upper
Midwest by late in the day.  From the Ozark region and the mid
Mississippi into the lower Ohio valley -- precipitation is
expected to briefly begin as snow before changing over to a wintry
mix as the air column warms aloft.  Lingering cold air at the
surface is expected to support impactful ice accumulations across
portions of the Ozark region and mid Mississippi valley on before
changing over to rain by late Friday.  Expect primarily all snow
farther the north across the Upper Midwest.  The heaviest
accumulations are expected to center across southern to central
Minnesota into northern Wisconsin.  Models show a period of
moderate to heavy snow associated with the low-to-mid level warm
advection lifting northeast across the region Friday afternoon and
evening, followed by a second period Saturday morning supported by
strong low level convergence on the northwest side of the
departing system.  In addition to the synoptic forcing, a
prolonged period of southeasterly flow will support some lake
enhanced totals off of Lake Superior into the Arrowhead region of
Minnesota.

Day 3...

...Great Lakes/Northeast/Mid Atlantic...
Low pressure will slide east across the Upper Great Lakes on
Saturday.  As the system moves into the St Lawrence Valley, models
show a coastal low beginning to develop near Downeast Maine Sunday
morning.  This has the potential to produce a stripe of
significant snows across portions of northern New England. 
Meanwhile, as the low passes to the north, strong westerly flow
will support lake effect snow showers east of Lake Ontario, with
heavy accumulations possible across the Tug Hill region.  To the
south, snow changing to a wintry mix is expected to produce some
light snow and ice accumulations from the southern and central
Appalachians into the Mid Atlantic on Saturday.

Pereira