Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
359 PM EDT Sun Mar 27 2022

Valid 00Z Mon Mar 28 2022 - 00Z Thu Mar 31 2022

...Great Lakes...
Day 1...

Multi-spoked upper low over Quebec will send one last vort max
across the eastern Great Lakes tonight into early Monday which
will help continue some lake bands into NW PA/Chautauqua Ridge in
NY, central NY, the Tug Hill Plateau, and into the Green Mountains
in Vermont. Up to a few inches of additional snow are expected and
WPC probabilities of at least 4 inches are generally low. Snowfall
will end by Monday afternoon as high pressure moves into the
region.


...California to the Rockies...
Days 1-3...

Water vapor shows a deep and wrapped-up upper low in the mature
phase just west of 130W and roughly due west of SFO, which is
forecast to weaken as it comes ashore central CA Monday
afternoon/evening and eventually it will become an open trough on
Tuesday across the Four Corners region. 130+ kt jet will slide
through Southern California on Monday, putting much of the Sierra
in the left front exit region. This will promote broad-scale lift
which will combine with a somewhat narrow surge of moisture (PW
anomalies around +1 to +2.5 sigma) and upslope flow into the
Transverse Range and central/southern Sierra. With the progressive
flow, precipitation will largely end by late Tuesday (end of day
2) west of the CO River as heights quickly rise. Snowfall will be
modest at higher elevations (snow levels roughly 6000ft) with
1-2ft possible from around 7-8000ft and higher. Some significant
pass level snow is likely as well, including Donner Pass.

As the system moves eastward Day 2 into 3, upper dynamics will be
less favorable given the weakening trough but still robust jet
streak. Moisture surge from the East Pacific will flow into the
Rockies from the southwest, supporting PW values of +1 to +2 sigma
in some locations. The system will be in a transition phase as a
northern stream vort max over Canada dives into the Dakotas,
helping to elongate the precipitation shield to the northwest into
Day 3. Higher terrain will capitalize on the available moisture
from Utah/Arizona into Colorado where high snow levels above
8000ft late Monday will lower to around 7000ft as colder air moves
in. WPC probabilities for more than 6 inches of snow are moderate
(40-70%) in the White Mountains of AZ, the San Juans, the Uintas,
the Wind Rivers, and much of the CO Rockies.


...Upper Midwest through the Mid-Atlantic...
Day 3...

System exiting the West/Rockies will transition to a new phase as
a northern stream vort max diving into the backside of the
positively-tilted and sheared upper trough helps spur cyclogenesis
over the central Plains Day 3. Upper jet will take on a classic
"S-shape" curve by late Wednesday with its anticyclonically-curved
northern branch arcing into the western Great Lakes and its
southern branch across the Northwest Gulf. Though the degree of
phasing/interacting remains a bit uncertain as the features may
remain just offset in timing, guidance still supports a deepening
cyclone with broad warm advection to its east and overrunning
wintry precip to its northwest/north in colder air. Gulf moisture
will surge northward on 50-70kts flow bringing PW values of +1 to
+3 sigma and IVT around the 99th percentile into Michigan (higher
to the south) by the end of Day 3. Over Canada, a
quasi-banana-shaped high pressure will attempt to maintain cold
air closer to the Canadian border, especially northern MN into the
Arrowhead, but a mix of snow, sleet, and freezing rain is likely
across a large NW to SE swath from MN all the way through the
Great Lakes into parts of the interior Mid-Atlantic. Precipitation
types will likely be changeable through the event, so confidence
is low at this time range. Snow will likely be heavy and wet with
low SLRs, and ice accumulation may be more sensitive to
time-of-day as it is almost April. Through the end of Day 3 (00Z
31 March), WPC probabilities of at least 4 inches of snow are up
to about 40% near International Falls, MN and above 50% in the
Arrowhead, with more accumulation into Day 4. Freezing rain is
likely in a broad area with the potential for more than 0.1" over
parts of northern Wisconsin into Michigan. This may extend
southeastward into the Laurel Highlands of PA as well. WPC
probabilities of at least 0.25" ice exceed 10% over Lower Michigan.

Fracasso