Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
353 PM EDT Wed Mar 30 2022

Valid 00Z Thu Mar 31 2022 - 00Z Sun Apr 03 2022

...Central Rockies...
Day 2...

Modest height falls and PVA will accompany an upper level
disturbance swinging through the base of the parent trough on Day
2. A modest upper jet streak of ~100 kts will promote deep layer
ascent thanks to diffluent flow within the jet streak's left front
quadrant, but total deep layer omega will remain fairly
progressive. Moisture into the region will increase Thursday night
and into Friday as noted by an increase in mid-level RH and PWs
rising up to 1+ standard deviations above the climo mean. Modest
ascent combined with rapid progression of the system keeps
snowfall accumulations relatively light, but WPC probabilities for
more than 6 inches are 20-50% in the Absorokas and Big Horns on D2
with the highest probabilities focused in the tallest peaks.


...Upper Midwest, Great Lakes, Northeast...
Days 1-3...

A strengthening storm system in the Great Lakes will produce a
swath of wintry weather extending from the Midwest to the Upper
Great Lakes tonight and into Thursday morning. This storm system
is working with ample amounts of Gulf of Mexico moisture that is
highlighted by a 3-4+ sigma PW anomaly over northern Michigan this
evening. A deformation zone is set to form over south-central
Wisconsin and into Michigan's U.P. where the axis of heavy snow is
likely to set up. 12Z HREF probabilities for snow fall rates
>1"/hr range between 50-70% from southern and central Wisconsin on
north and east through the Green Bay area and into the eastern and
central U.P. between 06-12Z Thursday. As the low matures on its
northeast trajectory, colder air at low levels will run over Lake
Superior, prolonging the east-central U.P.'s bout of heavy snow
into the daytime hours on Thursday. Snowfall rates exceeding 1"/hr
may persist as late as 18Z Thursday before finally winding down as
the pressure gradient weakens due to the storm's progressive
movement. The U.P. of Michigan does contain the highest WPC
probabilities for >4" (>80% chance) while there is also up to a
60% chance for snow accumulations exceeding 8". It's worth
mentioning there is a 20-30% chance for snow accumulations
exceeding a foot, which lines up with the 13Z NBM's 90th
percentile which contains snow totals over a foot as well. Central
Wisconsin also has a chance for heavy snowfall accumulations with
a 40-60% chance of snow totals >4" for Day 1. The combination of
heavy snow and gusty winds may lead to near whiteout conditions
and drifting snow in affected areas.

The ongoing significant ice event in parts of northern Michigan
and Michigan's U.P. will transition to primarily rain by this
evening, but some lingering freezing rain/sleet may stick around
in the east-central U.P. before precipitation changes back to snow
later tonight.

...Great Lakes, Ohio Valley, Northeast...
Days 2-3...

An upper level shortwave diving south and east from northern
Minnesota tonight will deepen as it interacts with a small but
potent vorticity maximum tracking through Missouri Thursday
morning. As this trough races east, scattered snow showers will
envelope the Lower Great Lakes Thursday afternoon and into the
evening hours. The trough progresses towards the Northeast Friday
morning as lapse rates steepen to ~9C/km and an influx of low-mid
level moisture arrives, resultimg in widely scattered snow
showers. SBCAPE up to 100 J/kg may manifest over parts of
Pennsylvania and upstate New York and snow squall parameters of 3+
are shown on the 12Z GFS & 12Z NAM. This suggests the potential
snow snow squalls in parts of the interior Mid-Atlantic and
Northeast Friday morning and afternoon. It is worth noting that
the air-mass aloft is not in the same class of the one that
triggered intense snow squalls this past Monday. However, lapse
rates are steep and enough low level moisture is available to
support the potential for heavy bursts of snow and gusty winds
embedded within these snow showers, potentially leading to
dramatic drops in visibility and light accumulations.

As the lobe of vorticity tracks across the Northeast on Friday,
snow showers will also break out downwind of Lakes Erie and
Ontario, as well as in the favored upslope areas of the
Adirondacks and northern New England. Some of the highest
elevations may pick up as much as 4" in spots. Snow showers look
to wind down throughout the Northeast by Friday night.

Mullinax