Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
506 PM EDT Mon Mar 28 2022

Valid 00Z Tue Mar 29 2022 - 00Z Fri Apr 01 2022

...California to the Central/Southern Rockies...
Days 1-2...

A closed low will cross southern CA tonight before opening into a
wave over AZ early Tuesday, crossing the southern Rockies Tuesday
evening. Ahead of this main wave, a shortwave trough spins off the
low by this evening, reaching the southern Rockies late tonight.
An overlap of ascent from the low/trough and subtropical jet with
ample Pacific moisture streaming in ahead of the low will lead to
heavy mountain snow, with snow levels generally around 6000 ft
over CA/AZ and closer to 8000ft for CO/NM. Day 1 snow
probabilities are moderate for over 6" for the higher southern CA
ranges and the eastern side of the Sierra Nevada and ranges of
central NV (from cyclonic flow north of the low) and moderately
high for the ranges of southern UT/the Mogollon Rim of AZ/the
ranges of western CO.

Lee side cyclogenesis is over eastern CO tonight with enhanced
northeasterly flow into northeast CO/southeast WY Tuesday which
brings the CO Front Range and Sangre de Christos into moderate Day
2 snow probabilities over 6". There are some 2" Day 2 snow
probabilities onto the Palmer Divide/Raton Message.


...Northern Plains...Upper Midwest to the Central Appalachians and
into the New England...
Days 2-3...

Continued confidence in a rather complex longwave trough/low
development over the Upper Midwest by Thursday morning through the
interaction of 3 or 4 mid-level shortwave trough that will produce
a long duration winter weather event over the Upper Midwest and
Great Lakes Tuesday night through at least Thursday.

The leading shortwave trough from the closed low over southern CA
pushes northeast from the southern Rockies across the central
Plains Tuesday which interacts over the northern Plains with a
northern stream shortwave trough shifting southeast from the
Canadian Prairies Tuesday night. This directs the main wave from
the Southwest to shift east across the southern Plains Tuesday
night and should allow a closed low to form somewhere near IA
Wednesday that lifts to the Upper Midwest Wednesday night. Further
reinforcement from the north on Thursday allows more development
as it likely lifts into Ontario. There is general agreement among
12Z guidance for this scenario though the 12Z GFS is a bit of an
outlier with forming the initial low earlier than the 12Z
ECMWF/UKMET/CMC which are in pretty good agreement synoptically
speaking. Regardless of the exact evolution, moist advection out
of the Gulf of Mexico is progged to be intense on 850mb winds
surging towards 50kts producing IVT exceeding +4 standard
deviations according to the NAEFS ensemble tables lifting into the
Great Lakes. This deep moisture combined with impressive deep
layer ascent will spread rounds of moderate to heavy precipitation
northward, and a mix of snow, sleet, and freezing rain is likely
late Tuesday through Wednesday night with wrap around snow
continuing Thursday potentially into Friday.

With the complex forcing/low structure producing uncertainty,
defining the likely narrow transition zones between wintry mixes
remains difficult. However, some refinement was able to be made
with this forecast. Day 2 snow probabilities for over 4" are 20 to
40% over the eastern border of the Dakotas and northern MN for
bands north of the initial surface low. Day 2 moderate ice
probabilities for over 0.1" extend east of the low across the
Upper Midwest along a low level boundary between the departing
Canadian high and warm air advection over north-central WI into
the western U.P. of MI and moderately high over the northern L.P.
of MI. Some low probabilities for over 0.1" are also over eastern
OH to west-central PA and western MD. 

The main surface low shifts across MI Wednesday night into
Thursday with notable wrap around snow along a pivoting axis
expected. This brings high Day 3 snow probabilities for over 4"
south of Lake Superior (with moderate probabilities for 8") mainly
over the western U.P. with low probabilities stretching into
central WI. Day 3 ice probabilities over 0.1" are low to moderate
over the Upper Midwest and low over interior terrain of the
Northeast - the Adirondacks and Green/White Mtns.


Jackson