Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 PM EST Mon Mar 07 2022

Valid 00Z Tue Mar 08 2022 - 00Z Fri Mar 11 2022

...Northeast & Mid Atlantic...
Days 1-2...
The first storm system to impact the Northeast will be
strengthening as it tracks across central Maine this evening.
Strong vertical motion beneath the right-entrance region of a
250mb jet streak will be positioned over northern Maine.
Meanwhile, 850-700mb frontogenesis will result in a band of
heavier snowfall between 00-06Z tonight. WPC's Snowband
Probability Tracker (SPT) does show a narrow deformation zone
where snowfall rates over 1"/hr are possible. Meanwhile, just to
the south, sub-freezing temperatures at the surface and warm
southerly flow several thousand feet up will result in a profile
favorable for freezing rain. Given the storm's fast progression,
ice accumulations will generally remain below a tenth of an inch
across north-central Maine.

Focus then shifts to an upper trough ejecting out of the Four
Corners region early Tuesday morning that quickly tracks across
the South Central U.S. by Tuesday afternoon. As WAA increases
within the 850-500mb layer out ahead of the neutrally-tilted upper
trough, the 250mb jet streak over the Northeast eventually exceeds
150 kts by 06Z Wednesday. Precipitation is forecast to breakout in
the Mid-Atlantic and the central Appalachians as vertical motion
becomes increasingly robust. Boundary layer temperatures will be
above freezing but drier dew points are expected, which combined
with stronger vertical ascent into the column will result in
dynamic cooling and temperatures wet-bulbing to just below
freezing west of I-95. Elevation will play a critical role in
accumulations given the milder boundary layer conditions along and
just west of I-95 and recent warmth over the last few days. Latest
WPC probabilities indicate up to a 20% chance for >4" of snowfall
in the highest elevations of western Virginia, eastern West
Virginia, and points north into western Maryland and central
Pennsylvania. It is worth noting there have been recent trends in
guidance that suggest the potential for banding in the vicinity of
the 850-700mb front over northern Virginia and into northern
Maryland. Should this occur, heavier rates could lead to increased
snowfall accumulations in future forecasts, especially in the Blue
Ridge and central Appalachians. 

...Western U.S.... 
Days 1-3... 
A pair of shortwave troughs will amplify a broader scale trough
that is set to track through the Northwest on Day 1, dig into the
central Rockies and as far west as the Great Basin on Day 2, and
amplify further into the Four Corners region by Day 3. As the
broader scale trough deepens, diffluent 700-500mb flow will
support the development of snow from the Cascades to the Northern
Rockies on Day 1. Localized accumulations exceeding a foot are
possible, especially across the northern Idaho ranges, including
the Bitterroot and Clearwater mountains. As a strong area of high
pressure in the Canadian Prairies also dives south on Day 2,
easterly upslope flow and much below normal temperatures for
mid-March will further assist in causing periods of heavy snow for
the Wasatch, Teton, Wind River, Bighorn, Park, and Laramie Ranges.
WPC probabilities for snowfall >8" on Day 2 are up to 50% in these
ranges with the Wasatch featuring slightly higher probabilities
(>70% chance). The trough continues to amplify as a trailing
vorticity maximum dives south into the Southwest on Day 3. Heavy
snowfall may occur as far south and west as the Mogollon Rim in
northern Arizona, but the best chances for snow totals >8" reside
in southwest CO. More specifically, the San Juans have a moderate
chances (>50%) for snowfall totals >8" through Day 3. In total
across all three days, the higher mountains ranges of Wyoming,
Utah, and the Colorado Rockies could end up with 1 to 2 feet of
snow by Thursday evening. Heavy snowfall rates and gusty winds may
result in near-whiteout conditions and make for treacherous travel
conditions.

...Central Plains...
Days 2-3...
As the upper trough in the West continues to amplify and dig
southeast, a wave of low pressure will strengthen in lee of the
central Rockies Wednesday afternoon. A tightening 850-700mb front
and diffluent flow in the left exit region of a jet streak over
the Four Corners region will result in banded areas of snow,
falling heavily at times Wednesday afternoon and into Wednesday
night. By Thursday, periods of snow will blanket parts of the
central Plains and Midwest but diminishing upper level support
should lead to diminishing snowfall rates by the time the shield
of snow reaches the Mississippi River. Latest guidance has come in
with slightly colder temperatures aloft but deterministic guidance
continue to show differences in placement of where the heaviest
banding of snow sets up. Latest WPC probabilities indicate as high
as a 60-70% chance for snow totals >6" in southwest Nebraska.
Chances for snow totals of 6" or more are as high as 50% from
southeast Wyoming and across southern Nebraska. There are
solutions that depict snowfall amounts as high as a foot in parts
of southwest Nebraska and it is still possible for higher snowfall
totals in the 8-12" range to expand should guidance come into
better consensus on where the deformation zone sets up in the
coming days.
 
Mullinax