Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
248 PM EST Thu Feb 03 2022

Valid 00Z Fri Feb 04 2022 - 00Z Mon Feb 07 2022

...Pacific Northwest and Northern Rockies...
Days 1/2...

A modest shortwave embedded within confluent flow and ahead of a
building ridge across the Pacific will spread onshore Friday
bringing moisture and ascent into WA state before spilling into
the Northern Rockies on D2. Snow levels during this time will be
generally around 3000 ft, and while the feature is likely to be
fast mover, it should have enough of an overlap of forcing and
moisture to produce heavy snow. WPC probabilities are high for 6+
inches on D1 across the WA Cascades, and then high on D2 across
parts of the Northern Rockies. Moderate snowfall is likely at
several of the mountain passes including Stevens, Snoqualmie, and
Marias.


...Mid-South through the Northeast...
Days 1/2...

Ongoing expansive winter storm will continue to shift to the
northeast tonight and Friday before shifting offshore Friday
night. The surface wave is likely to move from the TN VLY tonight
to just south of New England Friday evening, along a cold front
which will gradually be shifting southeast with time through New
England and the Mid-Atlantic. Moisture will be plentiful in the
vicinity of this front and low pressure, upon which deep layer
ascent will be impressive through isentropic upglide, height
falls, and robust RRQ diffluence behind a strong jet streak moving
into Canada. The guidance today has in general been a little too
warm compared to upstream observations, so while this still
appears to be a snow, sleet, and freezing rain event, the threat
for heavy freezing rain seems to be waning in place of very heavy
snow and significant sleet.

Across Upstate NY and trough much of Northern and Central New
England, a persistent band of frontogenesis will align across the
region aiding the already strong lift. Within this belt, snowfall
will likely reach 2"/hr at times, and many hours of heavy snow are
likely. The aftn guidance has increased snowfall potential across
this region, with the NBM 90th% now suggesting more than 20" in
some places while the HREF mean is over 15" in VT and NH. This has
caused an uptick in accumulations, and WPC probabilities for 8+
inches are above 80% from Upstate NY through central ME, and it is
likely many areas will exceed 15" with a few spots to 20"
possible, most likely in the Greens and Whites of VT/NH. South of
the heaviest snow, CAA behind the front will cause rain to change
to freezing rain and sleet, and while there is still some
discrepancy in the timing amongst the guidance which causes
differences in IP/ZR amounts, the trends have been for more sleet
vs freezing rain today. Moderate to heavy freezing rain is still
likely from eastern KY through parts of Southern New England,
especially in the Poconos and Catskills. WPC probabilities for
0.1" across this corridor are as high as 80%, with probabilities
exceeding 50% for 0.25" in the aforementioned terrain. North of
the freezing rain but south of the snow, an extended period of
sleet is becoming more likely as noted by HREF dominant p-type
probabilities. While sleet is counted as snow in accumulation so
the WPC snow probabilities do not adjust, it is important to note
that 1-2" with locally up to 3" of sleet is possible, especially
from central NY through Massachusetts.


...Far northern Minnesota...
Days 2-3...

A fast moving low pressure dropping out of Alberta will clip ND
and MN Saturday with a branch of robust WAA ahead of this feature
leading to expanding precipitation falling as moderate to heavy
snow. The speed of the system will limit total snowfall, but PWs
more than +0.5 standard deviations above the climo mean will allow
for at last moderate snowfall rates which could accumulate quickly
in the extremely cold column. WPC probabilities for 4 inches are
10-20% along the Canada/MN border.

Weiss


~~~ Key Messages for Feb 1-4 Winter Storm ~~

-- An expansive winter storm will shift into the Northeast tonight
with heavy snow, sleet, and freezing rain.

-- Freezing rain and sleet over the Mid-South will progress
northeastward into the Northeast this evening. Significant ice
accumulation is possible from Pennsylvania eastward into Southern
New England. This could make for difficult travel conditions along
with some power outages and tree damage.

-- Heavy snow totals are expected from the eastern Great Lakes
through much of interior New York state eastward into central and
northern New England. Snowfall rates could reach 1-2 inches per
hour tonight and early Friday.

-- Locations impacted by snow and/or ice from this storm will
experience below freezing temperatures into the weekend.