Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 PM EST Tue Jan 22 2019

Valid 00Z Wed Jan 23 2019 - 00Z Sat Jan 26 2019


...Great Lakes...
Days 1-3...

Surface low development ahead of a deep trough will continue
across northern MO this evening before tracking northeast to MI
through Wednesday morning. Strengthening divergence aloft and deep
low to mid-level frontogenesis will result in locally heavy snow
bands with the heaviest amounts in the developing TROWAL north of
the low from IA/southern WI and across the northern LP of MI.
Moderate WPC Day 1 probabilities for six inches are across
southern WI to Lake Huron. A wintry mix along the southern extent
of the heavier snows is expected to produce some light ice
accumulations from MI to southern Michigan.  The low is forecast
to track into eastern Canada with drier conditions late Wednesday
into early Thursday before an amplifying shortwave over central
Canada sends a weak surface wave and reinforcing shot of colder
air across the upper Great Lakes Thursday, supporting the return
of lake effect snow showers Thursday night into the weekend.


...Southern and Central Appalachians, Northeast...
Days 1-2...

Low pressure moving across MI Wednesday morning will continue to
track to the northeast across eastern Ontario into Quebec into
Thursday. Precipitation ahead of the low is expected to begin as a
wintry mix, producing some light snow/ice accumulations across
portions of northern New York and New England before changing over
to rain on Wednesday.  The trailing cold front will move from the
Ohio and Tennessee valleys into the Appalachians on Wednesday. A
surface wave moving north along the front is expected to send
moisture spreading west of the front, supporting a changeover from
rain to snow and freezing drizzle before precipitation draws to a
close. This should produce some light snow/ice accumulations
across portions of the Tennessee and Ohio valleys into the central
and southern Appalachians Wednesday night into Thursday morning.
Day 2 WPC probabilities show only low probabilities for
accumulations of 4-inches or more from the Ohio valley into the
central Appalachians.

As the wave continues to track to the north, portions of the
interior Northeast should see another round of light snows before
the system tracks into Atlantic Canada late Thursday. Higher
elevations in the Adirondacks and northern New England have
moderate probabilities for 4-inches on Day 2. Wrap around snow
ends over ME Thursday evening with lake effect particularly from
Lake Ontario continuing for Day 3.


...Pacific Northwest to the Northern Rockies...
Days 1-2...

Locally heavy snows are expected across portions of the northern
Cascades, as well as northeast Washington into northern Idaho, as
warm advection precipitation spreads out ahead a well-defined
shortwave dropping southeast into WA tonight. This system shears
out as it moves to the southeast, along with a cold front pushing
south the northern Rockies should produce locally heavy mountain
snows along the northern Rockies, from northern Idaho to northern
Colorado, Wednesday into early Thursday. High probabilities for a
foot are in the Day 1 WPC probabilities for the northern Cascades
and northern ID. Moderate probabilities for 8-inches are on tap
for the CO Rockies for Day 2.

Jackson