Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
424 PM EST Fri Feb 26 2021

Valid 00Z Sat Feb 27 2021 - 00Z Tue Mar 02 2021


...Pacific Northwest to the Northern and Central Rockies...
Day 1...
Mid-level energy embedded within northwest flow will support
additional periods of locally heavy snow from the Cascades to the
northern Rockies Friday evening, with WPC PWPF indicating
additional accumulations of 8-12 inches likely, and locally higher
totals possible, for portions of the Cascades, Blue Mountains and
Bitterroot Range.  Meanwhile, mid-level energy moving through the
base of an amplifying trough will support the potential for
periods of heavy snow farther to the southeast from the
northeastern Nevada mountains to the central Rockies beginning
this evening.  Periods of snow are then expected to continuing
into Saturday as the previously noted upstream energy digs to the
southeast.  Areas impacted are expected to include the eastern
Idaho to western Wyoming ranges, the northern and central Utah
mountains, and south-central Wyoming to north-central Colorado
mountains.  WPC PWPF shows accumulations of 6-12 inches, with
locally heavier possible, for those areas.

As the upper trough begins to split, with the northern stream
segment moving east of the Rockies into the Plains, while the
southern stream wave digs farther to the south, the potential for
heavy snow is expected to decrease by early Sunday.  From Sunday
and continuing through Monday, a well-defined ridge is expected to
support dry weather as it moves east across the region.

...Upper Midwest/Great Lakes...
Day 2...
A northern stream shortwave emanating from the trough in the West
is expected to track east-northeast from the central Plains late
Saturday into the northern Great Lakes by late Sunday.  This will
likely bring a stripe of mainly light snows from Nebraska and
South Dakota into southern Minnesota and western Wisconsin
Saturday, with snows shifting northeast across northern Wisconsin
into the U.P. of Michigan on Sunday.  While widespread heavy
amounts are still not expected, models have been trending upward
with amounts, especially from southern Minnesota northeastward. 
Guidance has trended more amplified with the wave as it moves
across the region, along with showing an increasing signal for
mesoscale banding, supporting a narrow stripe of heavier amounts
developing across the region on Sunday.

...Northeast...
Day 1...
Weak southern stream energy lifting from the southeast, along with
a more defined northern stream trough lifting across the Great
Lakes will support precipitation spreading north from the central
Appalachians and Mid-Atlantic into the Northeast Friday night into
Saturday, with precipitation continuing across northern New
England into late in the day.  As high pressure retreats, a wintry
mix at the onset is expected to change over to rain across most
locations.  Exceptions may include the higher elevations of
northern New Hampshire into central and northern Maine, where
precipitation may remain mostly snow and the probabilities for
accumulations of 4-inches of snow or more are highest.

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

Pereira