Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EST Mon Feb 28 2022

Valid 12Z Mon Feb 28 2022 - 12Z Thu Mar 03 2022

Corrected to fix time period references

...Pacific Northwest...
Days 1-3...

Strong atmospheric river event will bring copious moisture to the
Pacific Northwest with appreciable amounts into northern Idaho and
northwestern Montana but with mild temperatures and high snow
levels over the Cascades especially Day 1 (above all pass levels
and up to about 8000-9000 ft). Closer to the Divide, snow levels
will rise quickly today to about 7000 ft as snow changes to rain
up in elevation. Precipitable water values will be well above
normal (about +3 sigma even into northern Idaho this afternoon)
and total amounts on just Day 1 may be will be well over a foot at
high elevations and closer to several feet at the highest peaks in
the Washington Cascades. By Day 2 the moisture plume will sink
southward into Oregon as the boundary offshore waits for upstream
troughing, resulting in much less QPF and snowfall overall. On Day
3, troughing is forecast to elongate just east of 130W and bring a
bit more QPF/snow to the Oregon Cascades as cooler air moves in
resulting in snow levels dropping back to about 4000ft to the
north and 5000ft to the south.

...Northeast...
Days 2-3...

Upper low over Hudson Bay will coax a shortwave around its base
through the Great Lakes and into the Northeast Day 2. Surface low
pressure may be able to capitalize on enough digging in the
mid-levels and moisture pull from the Atlantic to bring a few
inches of snow to northern NY eastward to Maine as it zips
through. WPC probabilities of at least 4 inches of snow are low,
generally 10-40%, but some areas could see enhancement via upslope
across the northwestern Adirondacks and Green and White Mountains.
Will have to monitor Maine for a narrow window of more modest snow
as the low deepens just a bit overhead coincident with 0.50" PW in
the Gulf of Maine overnight Tue into early Wed.

On Day 3, another clipper will track in a similar path from the
Upper Midwest across the Great Lakes and into the Northeast, but
with stronger dynamics and a bit more QPF. Upper jet stream
~130kts may support more robust cyclogenesis across southern
Ontario late Wed as the low tracks a bit farther south than its
predecessor through central or southern New England. Snowfall will
focus along its cold front through western, central, and northern
New York Day 3 but with generally light amounts of a couple/few
inches. WPC probabilities for at least 4 inches of snow are low
(10-30%) but may see some enhancement east of Lake Ontario and
into southwestern New York with some elevation gain.


For Days 1-3, the probability of significant icing of at least a
quarter of an inch is less than 10 percent.


Fracasso