Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
327 AM EDT Sat Mar 26 2022

Valid 12Z Sat Mar 26 2022 - 12Z Tue Mar 29 2022

...Upper Midwest/Great Lakes/Central Appalachians...
Days 1-3...

Longwave trough centered over the Great Lakes will maintain broad
cyclonic flow across the East into early next week. Within this
longwave trough, a potent closed mid-level low will dig from
Minnesota to Ohio tonight, and then shift into the Canadian
Maritimes while filling on Sunday. Impressive height falls and PVA
will drive robust synoptic ascent, while a surface low moving
along the international border drags a cold front eastward. While
the synoptic lift is impressive, available moisture is modest
noted by PW anomalies of -0.5 to -1 standard deviations from the
climo mean. This suggests that despite a broad swath of light
snow, the heaviest snow will be confined to the LES snow bands and
into upslope regions where moisture is enhanced, or can be more
efficiently squeezed out into snow.

On D1, the heaviest snowfall is likely SE of Lake Erie along the
Chautauqua Ridge where LES will also upslope to produce heavy snow
rates, especially beginning this evening and persisting through
Sunday aftn. WPC probabilities for more than 4 inches here are
above 70%, and locally more than 8 inches is possible.
Additionally heavy LES is likely into the Tug Hill Plateau,
eastern U.P. southeast of Lake Michigan, and near Traverse City,
MI, where WPC probabilities for more than 4 inches is 10-30%. Also
on D1, enhanced moisture from the lakes will be wrung out
efficiently by prolonged upslope flow into the Central
Appalachians of WV into the Laurel Highlands of PA where more than
6 inches of snow is likely in the higher terrain. By D2, the
continued cyclonic flow and CAA will drive more LES east of Lake
Erie into the Chautauqua Ridge and east of Lake Ontario along the
Tug Hill Plateau and into the western Adirondacks. Additionally
snow accumulations may reach 4 inches on D2, and storm total may
exceed 12 inches near Erie, PA.


Additionally, guidance continues to suggest scattered convective
snow showers developing through Saturday evening as the main PV
anomaly swings eastward from the Ohio Valley into the
Mid-Atlantic. A nearly saturated column with steep lapse rates and
some marginal but sufficient instability favors convective snow
showers beneath the cold pool aloft, with briefly heavy snowfall
rates likely. Although likely to be isolated, the combination of
gusty winds and heavy snowfall may produce embedded snow squalls
as well.


...Sierra Nevada...
Days 2-3...

An anomalously deep upper low characterized by 700mb heights of
more than 3 standard deviations below the climo mean will shift
onshore central CA Monday accompanied by a surface low which will
approach the coast D3 as well. Downstream of this feature, warm
and moist advection will surge onshore as a weak AR (IVT < 500
kg/m/s) within confluent mid-level flow and the LFQ of a 130kt
upper jet streak. Where this flow upslopes into the terrain, heavy
snowfall will become likely late D2 and especially D3 as the core
of the AR shifts across the Sierra. Moderate snowfall is likely
D2, but on D3 WPC probabilities for more than 6 inches of snow
eclipse 70% above 6000 ft, with locally more than 12 inches
possible in the highest terrain, and this will likely produce
hazardous travel across most of the Sierra Passes.


Weiss