Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
421 PM EST Thu Dec 15 2022

Valid 00Z Fri Dec 16 2022 - 00Z Mon Dec 19 2022

...Significant winter storm gradually transitioning from the
Northern Plains/Upper Midwest to the Northeast...

Days 1-2...

...Northern Plains/Upper Midwest...

A significant winter storm continues to unfold across the Northern
Plains and Upper Midwest as a strong area of low pressure lingers
over the region and gradually begins to wind down. Thee vertically
stacked system continues to have multiple shortwave vorts/impulse
rotating around it that will continuing to maintain the threat of
moderate to locally heavy snowfall tonight and early Friday across
the Dakotas in particular and to a lesser extent adjacent areas of
the Upper Midwest involving MN/WI. The deep layer low center will
be shifting east across the Upper Great lakes region by Saturday,
and much of the additional snowfall potential at least for the
Upper Midwest by Friday night and Saturday will be light as
forcing steadily weakens, mid-level dry air wraps around the
system, and the system begins to pull away. However, the snowfall
over the next 24 hours will be on the order of 4 to 8 inches
locally across the Dakotas, and strong northwest winds on the
western side of the low center will continue to result in strongly
reduced visibility with blizzard conditions likely to persist at
least into Friday morning. Several inches of additional snow are
expected for areas of MN/WI will also likewise couple with strong
winds for blowing snow concerns heading through Friday and into
Saturday.


Days 1-3...

...Great Lakes/Northeast...

The large and evolving winter storm over the Northern Plains and
Upper Midwest will continue to gradually translate downstream into
the Northeast as the leading edge of height falls/troughing favor
developing low pressure across the Mid-Atlantic coastal plain
which is forecast to deepen and move northeast just to the
southeast of Long Island by Friday evening and then across the
Gulf of Maine on Saturday before exiting into far southeast
Canada. Already there is a large swath of moderate to heavy
precipitation including a wintry mix of sleet and freezing rain
lifting through the northern Mid-Atlantic, and this will be
encountering an increasingly deep cold airmass farther north
across interior sections of New York and New England going through
tonight and into Friday. There is a notable punch of warm air
aloft in the 750/850 mb layer at least initially that could favor
some mixed precipitation at least through early this evening for
areas of northern PA and southern NY, but cold air will become
increasingly tucked in around the northwest flank of the
aforementioned surface low, and coupled with increasing mid-level
dynamical ascent, this warm nose aloft will be eroding. Thus,
gradually areas of northern PA and southern NY, and especially the
adjacent areas of central to northeast NY and central New England
should see any mixed precipitation rather quickly changing over to
all snow, with snow becoming moderate to heavy at times. However,
the boundary layer thermals across the Hudson Valley and up
through the Capital District are likely to still be relatively
warm and there will be a tendency for rain or a rain/snow mix to
linger across these areas for longer at least for tonight before
becoming all snow Friday morning. The environment from midday
Friday through early Saturday will become increasingly conducive
for some banded snowfall potential owing to strong 850/700 mb
fronotgenetical forcing and pockets of negative EPV. The greatest
potential for this will tend to be across eastern NY up across
VT/NH and western ME. Some occasional 1 to 2 inch/hour snowfall
rates are expected with this evolution and this will be aligned
with the strengthening mid-level deformation zone that will be
unfolding around the northwest flank of a new 850/750 mb low
center that crosses southern New England and gradually the Gulf of
Maine.

Very heavy snowfall totals of 1 to 2 feet are expected across much
of central/northeast NY, VT/NH, and western ME with an emphasis on
the Adirondacks, Mohawk Valley, Catskills, and the Green and White
Mountains. Some spotty locations over these areas with the aid of
robust upslope flow into the terrain may see in excess of 24
inches. The Berkshires of western MA may also see some spots of at
least a foot of new snow as the deformation zone clips this
region. The latest PWPF shows moderate to high probabilities (40%
to 70%+) of seeing 12+ inches across many of these areas with a
sharp cut-off in probabilities for heavy snow down across the
lower elevations.

As the Northern Plains/Upper Midwest portion of this larger scale
storm begins to wane, and as the secondary Northeast low center
begins to edge away, the theme will be rather strong cold air
advection with cyclonic west to northwest flow over the relatively
warm/ice-free areas of the Great Lakes, and this will set the
stage for areas of heavy lake-effect snow. All of the downwind
areas of the lakes will be impacted, but the heaviest amounts over
the next 2 to 3 days will be off Lake Michigan and especially Lake
Erie and Lake Ontario. Convergent low-level flow along with a
relatively moist mid-level column associated with the pre-existing
trough/closed low evolution will set the stage for some enhanced
long-fetch lake-effect snowbands that will be capable of producing
2 to 4 inch/hour snowfall rates. Areas near and to the south of
Buffalo, NY downwind of Lake Erie, and especially the Tug Hill
Plateau downwind of Lake Ontario may see 2 to 3+ feet of new snow
just for the Saturday and Sunday time frames combined.


Key Messages for December 9-17 Winter Storm:
- Blizzard conditions will continue into Friday across the
Northern Plains and parts of the Upper Midwest as additional areas
of heavy snow and strong winds gusting to 45-60 mph persist.

- Near zero visibility and snow covered roads will maintain
difficult to impossible travel, along with scattered power
outages, and harsh livestock conditions.

- Increasing winter storm impacts are expected tonight and Friday
across the interior of New York and New England as the large storm
system gradually transitions from the Northern Plains and Upper
Midwest to the Northeast.

- Very heavy snowfall rates reaching 1 to 2 inches/hour will be
likely across areas of interior New York and central New England
with storm totals reaching 1 to 2 feet by Saturday across portions
of the Adirondacks, Mohawk Valley, and the Green and White
Mountains. Dangerous travel conditions and scattered power outages
are expected from the snow.

- Lake-effect snow will develop downwind of the Great Lakes in the
wake of the storm across parts of western New York south of
Buffalo, and near the Tug Hill Plateau. Very heavy snowfall
impacts will begin Saturday and continue into Sunday across these
areas.

Orrison