Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
306 PM EST Wed Nov 09 2022

Valid 00Z Thu Nov 10 2022 - 00Z Sun Nov 13 2022


...Northern High Plains into Upper Mississippi River Valley and
Western Great Lakes...
Days 1-3...
This afternoon, a deep upper trough continues to move across the
Intermountain West, with an upper low centered over southern
Idaho.  A well-defined shortwave moving through the base of the
broader scale trough is expected to move across the Four Corners
region before lifting northeast and phasing with the low to the
north overnight into tomorrow.  This will support a surface low
developing and tracking northeast from the central High Plains
this evening, across Nebraska overnight, before reaching southern
Minnesota tomorrow morning.  The latest guidance continues to
signal a significant winter storm, with heavy snow and blizzard
conditions likely to develop across portions of the Dakotas
tomorrow.  Supported in part by favorable upper jet forcing and
strong low-to-mid level frontogenesis, the latest HREF guidance
indicates that banded snowfall, producing rates of 1-2 in/hr, is
likely to set up across portions of central to eastern North
Dakota early tomorrow, before shifting into northwestern Minnesota
by the afternoon.  This is where the heaviest snow accumulations
are most likely to occur, with the latest WPC PWPF indicating high
probabilities (greater than 70 percent) for accumulations of 8
inches or more extending from the central North and South Dakota
border into northwestern Minnesota.  Within this area, heavier
amounts of a foot or more can be expected, with the highest
probabilities centered across central North Dakota.  In addition
to the heavy snow, a tightening pressure gradient developing on
the northwest side of the low will support strong winds, resulting
in blizzard conditions across parts of the Dakotas.  There also
remains a good signal for mixed precipitation developing southeast
of the heavy snow band, with warm air aloft supporting sleet and
freezing rain from north-central Nebraska to northeastern
Minnesota.  While widespread heavy accumulations are not expected,
WPC PWPF continues to show significant probabilities (40 percent
or greater) for ice accumulations of 0.10 inch or more centered
across northeastern South Dakota into southeastern North Dakota. 
Overall, the models have remained consistent with system, although
an additional small shift to the north was noted with the daytime
runs.  By tomorrow and continuing into the overnight, the system
is forecast to begin lifting out the northern Plains and upper
Midwest into western Ontario, with the threat for heavy snow
decreasing across northern Minnesota.

A much quieter period is expected late Friday into Saturday.  Low
level northerly flow/cold air advection is expected to reintroduce
the threat for lake effect snow showers, especially over the
western U.P.; however, widespread heavy snows are not expected.  


Key Messages for the Northern Plains and Upper Mississippi River
Valley:

-- A winter storm is expected to bring heavy snow, as well as
sleet and freezing rain, to portions of the northern High Plains,
Great Plains, and Upper Mississippi River Valley through Friday.

-- Heavy snowfall rates of 1-2"/hr are possible tonight through
Thursday from the Dakotas eastward into northwestern Minnesota.
Total snowfall will likely exceed 12" in some areas.

-- Blizzard conditions are possible across portions of the central
Dakotas due to the strong winds and reduced visibility. Travel may
become dangerous in some areas and scattered power outages are
possible.

-- Freezing rain and sleet are likely to the south of the heaviest
snow. Icing may be significant. This may produce hazardous travel,
disruptions to infrastructure, and scattered power outages.

-- Strong northeasterly winds over western Lake Superior may lead
to hazardous waves.

Pereira