Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
444 AM EST Sat Jan 18 2020

Valid 12Z Sat Jan 18 2020 - 12Z Tue Jan 21 2020


...Lower Great Lakes/Northeast/Central Appalachians/Mid Atlantic...
Low pressure moving across the mid Mississippi valley will
continue to deepen as it tracks northeast into the Upper Great
Lakes on Saturday.  Warm advection precipitation ahead of the low
is expected to move northeast from the Ohio valley into the Lower
Great Lakes, central Appalachians and northern Mid Atlantic region
Saturday morning.  Models continue to show a period of snow,
followed by sleet and freezing rain across much of the region. 
WPC PWPF shows snow accumulations of 4-6 inches likely across the
higher elevations of northwest to north-central Pennsylvania, with
lighter snow amounts in addition to accumulating ice farther
south.  WPC PWPF shows ice accumulations of 0.10 inch or more
likely along the Allegheny Mountains.

Precipitation will continue to spread north and east, with
low-to-mid level frontogenesis supporting periods of moderate snow
as it moves across New York into New England Saturday afternoon
into the evening the hours.  In addition to the larger scale
forcing, orographic enhancement is expected to bolster amounts,
especially from the Tug Hill region eastward into the southern
Adirondacks, Berkshires and Greens.  Low level westerly flow
developing across Lake Ontario Saturday may generate some lake
enhanced snows, further bolstering totals over the Tug Hill
region.

As the primary surface low moves east of the Upper Great Lakes,
models show a coastal low beginning to develop near the
southeastern New England coast.  Strengthening inflow into an axis
of low level frontogenesis may support a stripe of moderate snows
northwest of the low as it tracks along the northern New England
coast Saturday night into Sunday morning.

...Upper Great Lakes...
Enhanced convergence associated with a low level wave moving
east-southeast across northern Michigan is expected to enhance
snowfall potential across portions of Upper Michigan Saturday
morning.  As the low continues to move east, northwesterly flow in
its wake low will support lake effect snow showers that will
continue into Sunday.

...Pacific Northwest...
A warm front lifting across northeast across the region followed
by a weakening cold front will bring period of organized heavier
precipitation, including some heavy mountain snows to portions of
the Olympics and northern Cascades on Saturday.

Pereira