Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
438 AM EDT Thu Mar 24 2022

Valid 12Z Thu Mar 24 2022 - 12Z Sun Mar 27 2022

...Upper Midwest/Great Lakes/Central Appalachians
Days 2-3...

A shortwave digging out of Alberta, Canada will strengthen into a
closed low Saturday morning as it dives across MN and into the
Great Lakes. This feature will continue to dig southeast across
the Mid-Atlantic Saturday night into Sunday before weakening and
ejecting into Canada. This will drive an elongating trough across
the eastern CONUS, with a trailing jet streak strengthening to
130kts across the Upper Midwest Saturday night. A surface wave
beneath the mid-level impulse will move along the international
border and then into the Great Lakes, driving a cold front
southeastward to off the east coast Saturday, followed by a
reinforcing shot of cold air quickly in its wake. While forcing is
transient and moisture is somewhat limited, periods of heavy snow
are likely across the region.

On D2, some moderate snowfall is expected in the vicinity of the
primary shortwave across the MN Arrowhead. The guidance,
especially the high-res members, shows some loss of saturation
within the DGZ, but the global members are a little wetter, and
there is sufficient forcing to squeeze out any moisture as
snowfall. WPC probabilities for 4+ inches have fallen, bu are
still 10-20%. A secondary maxima of snowfall D2 is likely south of
Lake Superior and into the Bayfields Peninsula where CAA will
steepen the low-level lapse rates and produce moderate LES.

On D3, the trough axis swings eastward, and the associated CAA
will spread LES downwind of Lake Erie and Lake Ontario. Snowfall
may be heavy at times, especially along the Chautauqua Ridge and
westerns lopes of the Adirondacks where WPC probabilities for more
than 4 inches are 20-30%. A secondary maxima of snow, and likely
the the most impressive, is forecast along the upwind side of the
Central Appalachians near WV, western MD, and southwest PA, where
pronounced upslope flow will drive periods of heavy snowfall, at
least through Saturday evening before the DGZ begins to dry out.
In the higher terrain, WPC probabilities for more than 4 inches on
D3 are above 80%, and locally 10 inches of snowfall is possible.


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

A wave of low pressure across the Mid-Atlantic this morning will
slowly deepen as it shifts northeast into New England tonight and
then into Canada on Saturday. This low will deepen only slowly as
a broad but deep mid-level trough shifts eastward, and downstream
jet energy pivots eastward placing LFQ diffluence across the
Northeast. A modest warm front extending eastward from the surface
low will weaken, but persistent WAA on southerly low-level flow
will help to expand precipitation into New England through
Saturday, with a mix of snow and ice likely as the cold surface
high gradually retreats. The threat for heavy snow is likely
confined to far northern Maine, generally just Aroostook County,
as the low tracks along the coast. Guidance has gotten a little
colder tonight, but WPC probabilities for more than 4 inches of
snow remain above 50% just in far northern ME on D1 and D2.

Further to the south, the mix of sleet and freezing rain will
likely lead to rounds of accumulating ice, primarily in the
elevated regions of central and northern New England. WPC
probabilities for more than 0.1" of freezing rain are as high as
40% in the White Mountains of NH and Central Highlands of ME, with
lower probabilities extending into the southern Greens of VT and
Monadnocks of NH.


Weiss