Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EST Tue Mar 01 2022

Valid 12Z Tue Mar 01 2022 - 12Z Fri Mar 04 2022

...West...
Days 1-3...

Atmospheric river will focus its moisture plume (PWs around +2 to
+2.5 sigma) over southwestern Oregon Day 1 stretching
northeastward to northern Idaho and northwestern Montana. Snow
levels will remain quite high (6000-8000 ft from north/WA to
south/OR) so snowfall will be remain well above pass level. For
Day2, positively-tilted mid-level trough nearing 130W will push
eastward and split north-south, forming a closed low west of SFO.
Snow levels will start to lower, albeit slowly, down to pass level
over WA but with light accumulations. By Day 3, the upper low is
forecast to move into central or southern CA with a fair amount of
spread in the QPF (west-east timing uncertainty shows up quite
well in the ensemble spaghetti) and therefore snowfall. To the
north, northern portion of the trough may briefly close off as it
heads into western WA with most enhancement over northern ID into
northwestern MT. Formed a QPF and thermal best consensus amid the
spread.


...Northeast...
Days 1-2...

Multi-pronged upper low rotating around Hudson Bay/northern Quebec
will help send a couple clipper systems through the Great Lakes
into the Northeast the next few days. First system will bring warm
advection snow to New England starting this afternoon and evening
into early Wednesday as the surface low skirts astride the
U.S./Canadian border and through northern Maine. Northwest
flow/cold advection behind the low will enhance upslope flow into
the Adirondacks and Green and White Mountains. WPC probabilities
of at least 4 inches of snow are highest over northern Vermont and
low/moderate over northern NY and into Maine.

The second clipper may be more robust as it is driven by stronger
height falls and modest diffluence within the LFQ of an
approaching upper jet streak ~130kts. WAA ahead of the wave will
spread some snowfall northeastward, but again the heaviest snow
may be due to LES and upslope ascent within the trailing CAA. WPC
probabilities are 20-50% for 4+ inches downwind of Lake Ontario
and into the upwind side of the Adirondacks. As the surface low
deepens as it exits Maine, a secondary maximum in snowfall is
possible across Downeast Maine into early Thursday.


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


Fracasso