Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
423 PM EST Fri Mar 08 2019

Valid 00Z Sat Mar 09 2019 - 00Z Tue Mar 12 2019

...Western United States...

The southern stream shortwave that is forecast to impact the
Plains and Midwest will first produce some moderate to locally
heavy snows as it moves across the central Rockies Friday evening.
 WPC probabilities indicate the threat for additional locally
heavy accumulations across portions of the Colorado into the
northern New Mexico ranges late Friday into early Saturday.

Attention then turns to a series of shortwaves dropping south
through the eastern Pacific, with a broad positively tilted
circulation beginning to develop from the Pacific Northwest into
the eastern Pacific late Saturday into Sunday.  While the latest
models did not show a strong signal for widespread heavy
accumulations, there could be some locally heavy amounts develop
from the northwest California ranges and the Sierra eastward into
the Great Basin along a west-east oriented frontal zone.

Models then a show a consolidating upper low dropping south along
the California coast on Monday.  Moisture and forcing ahead of the
low look to be rather limited, however some of the higher terrain
area of the Southwest, as well as the southern Great Basin into
the Rockies may receive some locally significant snowfall
accumulations.

...Northern Plains to the Upper Midwest...

Overall, no significant changes from the previous forecast, with
models continuing to show a strong signal for widespread moderate
to heavy snow developing across the Dakotas Friday night and
Minnesota on Saturday, before shifting east into Wisconsin and the
Upper Peninsula of Michigan Saturday night into Sunday.

A southern stream trough currently moving across the southwestern
U.S. is expected to move east of the Rockies during the early
morning hours on Saturday and then assume a negative tilt as it
continue farther east into the Plains later in the day.  An
associated surface low developing in the lee of the central
Rockies is forecast to track east across the central Plains,
reaching the lower Missouri and mid Mississippi valleys by the
afternoon, before turning more the northeast toward the Great
Lakes late in the day.  Increasing warm air advection and
convergence ahead of a low-mid level wave moving east of the
northern Rockies is expected to support moderate snow moving east
across the Dakotas overnight.  Strong upper forcing ahead of the
approaching trough is expected to support intensifying snow from
the eastern Dakotas into the western Minnesota during the late
morning into the afternoon hours.  Models continue to show the
heaviest amounts centering along an inverted surface trough
extending north of the low into the region, with WPC Day 1
probabilities (ending 00Z Sunday) showing a Moderate Risk for snow
accumulations for 8-inches or more, with a Slight Risk for a foot
or more, centered along the South Dakota/Minnesota border.  Models
continue to show strong warm advection limiting snow amounts
farther to the south, with precipitation changing over to
sleet/freezing rain and some minor ice accumulations possible from
Nebraska eastward into northern Iowa, southern Minnesota and
southern Wisconsin during the Day 1 period.

Snows will continue to shift east into Wisconsin and northern
Michigan Saturday evening into Sunday morning, with the heavier
accumulations expected to occur earlier in the period before
forcing begins to wane in the cold sector. Heaviest accumulations
during the period are forecast to extend from the northern
Minnesota/Wisconsin border to the Upper Peninsula, where WPC Day 2
probabilities (ending 00Z Monday) indicate a Slight Risk for snow
amounts of 8-inches or more.

With the system lifting into eastern Ontario, northwest flow in
the wake of the system may result in some additional light
accumulations in the lee of Lake Superior late Sunday into early
Sunday.

...Northeast...

A warm front lifting north ahead of the previously noted low in
the Midwest will be the focus for light to moderate precipitation
spreading into the northern Mid Atlantic and Northeast Saturday
night and Sunday morning.  Retreating cold air is expected to
support a period of mixed precipitation, changing to rain from the
central Appalachians into the Northeast, with enough cold air
remaining in place to support mostly snow across northern Upstate
New York into northern New England.  WPC Day 2 probabilities
indicate a Moderate Risk for accumulations of 4-inches or more
mainly across the mountains of Upstate New York and central to
northern New England.

Pereira