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

Valid 12Z Tue Jan 22 2019 - 12Z Fri Jan 25 2019


...Central Plains to the Great Lakes...

Consensus of the overnight models has shifted a bit further south
with the shortwave moving east-northeast out of the central
Rockies Tuesday morning and its associated deformation band
developing from the central Plains into the upper Great Lakes
Tuesday into Wednesday.  Light to moderate snows are expected to
develop north of the surface low as it tracks east-northeast from
the central Plains into the lower Missouri and mid Mississippi
valleys by Tuesday evening.  Supported by strengthening divergence
aloft and deep low to mid level frontogenesis, heaviest amounts
are expected to center from central Iowa into southern Wisconsin,
with WPC Day 1 probabilities indicating a greater than 50 percent
chance for accumulations of 6-inches or more.  A wintry mix along
the southern extent of the heavier snows is expected to produce
some light ice accumulations from eastern Kansas 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,
supporting the return of lake effect snow showers.

...Ohio valley, Southern and Central Appalachians, Northeast...

Low pressure moving across the upper Great Lakes Wednesday morning
will continue to track to the northeast across eastern Ontario
into Quebec on Wednesday.  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 may produce some
light snow/ice accumulations across portions of the Tennessee and
Ohio valleys into the mountains Wednesday night into Thursday
morning.  WPC probabilities show only a Slight Risk for
accumulations of 4-inches or more from the Ohio valley into the
central Appalachians on Day 2.  As the wave continues to track to
the north, portions of the interior Northeast may see another
round of light snows before the system tracks into Atlantic Canada
late Thursday.

...Pacific Northwest to the Northern Rockies...

Locally heavy snows are possible 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 the region Tuesday night.  This
system as it continues to shear out to the southeast, along with a
cold front pushing south the northern Rockies may produce some
locally heavy mountain snows along the northern Rockies, from
northern Idaho to northern Colorado, Wednesday into early Thursday.

Pereira