Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
435 PM EST Tue Feb 23 2021

Valid 00Z Wed Feb 24 2021 - 00Z Sat Feb 27 2021


...Northern Plains to the Northeast...
Day 1...
A progressive, but dynamic shortwave will continue to move through
the northern Plains and Upper Midwest this evening, reaching the
northern Great Lakes Wednesday morning.  Strong low-to-mid level
frontogenesis combined with upper level forcing will continue to
support the potential for a narrow band of snow developing and
moving steadily east from eastern North Dakota through central
Minnesota, into northern Wisconsin and northern Michigan Wednesday
evening and overnight.  As the system moves east into southern
Ontario on Wednesday, northerly winds on the backside of the
system may offer a brief window for lake effect snow showers --
bolstering totals across portions of the U.P. and northern Lower
Michigan.  Highest totals through the Day 1 period (ending 00Z
Thu) are expected to center over the eastern U.P. and the Tip of
the Mitt -- with WPC PWPF showing 50 percent or greater
probabilities for accumulations of 4-inches or more across the
region. 

After moving across southern Ontario and Quebec during the day on
Wednesday, this system is expected to impact northern New York and
New England with generally light accumulations as it moves across
the region late Wednesday and early Thursday.

...Pacific Northwest to the Northern Rockies...
Days 1-3...
A shortwave trough dropping across the Northwest this evening may
produce some additional locally heavy snows early in the period
across portions of the northern Cascades, Blue Mountains, and the
northern Idaho ranges before dropping farther southeast during the
evening and overnight.  This will be followed by a brief period of
dry weather as a shortwave ridge moves across the region on
Wednesday into early Thursday.  Unsettled weather is likely to
return during the day on Thursday as another shortwave trough and
associated frontal band approach the region, with heavy snow
accumulations likely across the Olympics and northern Cascades by
late Thursday.  Heavy snow is likely to continue across the
Olympics and Cascades while expanding east into the Blue Mountains
and portions of the northern Rockies late Thursday through Friday.
 Guidance shows strong northwesterly flow ushering a string of
shortwaves across the region during that time.  Two day totals
ending late Friday are likely to exceed two feet across a large
portions of the northern Cascades, as well as parts of the Blue
Mountains and Bitterroot Range.

...Central Rockies/High Plains...
Day 2...
A shortwave trough moving across the Northwest Wednesday night is
forecast to continue to dig southeast through the Great Basin,
with snows developing across the central Rockies Wednesday night. 
As the system approaches, low level easterly flow will support
developing snows across the High Plains and along the foothills as
well.  While some areas along the Colorado I-25 corridor may see
local accumulations of 4-inches or more, widespread heavy amounts
along and east of the interstate are not expected.

For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Pereira