Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
256 PM EST Thu Mar 03 2022

Valid 00Z Fri Mar 04 2022 - 00Z Mon Mar 07 2022

...West...
Days 1-3...

A northern stream shortwave moving onshore WA state will advect
quickly to the east Friday bringing periods of moderate to heavy
snow along the Canada/US border. This system is fast moving and
has only modest moisture to work with, and WPC probabilities for
more than 4 inches are confined to the higher terrain near Glacier
NP on D1.

A far more significant shortwave will be diving down the CA coast
at the same time on D1, and it is this feature that will evolve
into an amplified longwave trough across the West through the
weekend. This shortwave will deepen into a closed low as it moves
onshore CA late D1, and then dig into the Great Basin D2, and
eventually the Four Corners by D3 with only slow filling at that
time. The pronounced longwave trough will help intensify
downstream jet streaks across the area, which when combined with
WAA ahead of low-level frontal boundaries will drive PWs upward to
+1 to +2 standard deviations across much of the West. This will
lead to widespread snowfall from the Sierra southeast to the
Mogollon Rim, northward through the Absarokas, and all the
surrounding terrain of the Great Basin and Intermountain West.
While there remains uncertainty into the exact evolution of this
trough due to complex shortwave and jet streak interactions, it is
likely that widespread heavy snow will occur both D2 and D3 with
WPC probabilities exceeding 30% for 8+ inches on D2 in parts of
the Sierra, Wasatch, ranges of NV, Wind Rivers, and CO/WY Rockies
including the Park Range. By D3, the heaviest snowfall shifts out
of the Sierra but WPC probabilities for 8+ inches remain 20-30% in
the Wasatch and San Juans. Event total snowfall is likely to
exceed 2 feet in the highest terrain of some of these ranges due
to multiple rounds of moderate to heavy snow.


...Central High Plains through the Great Lakes...
Days 2-3...

A complex trough will amplify across the Intermountain West this
weekend as a series of shortwaves interact to lower heights across
the region. Downstream of this trough, waves of energy will shed
northeast from the Rockies through the Central Plains and into the
Upper Midwest, with a minor shortwave followed by a more
impressive feature Saturday into Sunday. Both of these impulses
will bring a mixture of snow, sleet, and freezing rain.

The lead shortwave will have modest amplitude as it shifts
northeast across the Central Plains and into the Upper Midwest
Saturday morning. This feature will be accompanied by weak LFQ
upper diffluence but impressive warm and moist advection as
low-level confluent flow emerges from the Gulf of Mexico. This WAA
will drive a warm nose and expanding precipitation shield
northward into WI/MN, and the U.P., isentropically ascending a
retreating surface high pressure. Guidance has intensified this
feature today leading to greater precipitation, and a swath of
freezing rain exceeding 0.1" has a greater than 50% chance of
occurring from near Duluth, MN, eastward across northern WI, and
into the western U.P of MI.

A more significant system will develop rapidly in the wake of the
departing lead shortwave, as a closed mid-level low ejects out of
CO and shifts northeast towards Michigan late Saturday into
Sunday. Although this feature will open and weaken with time, it
will be accompanied by increasing upper diffluence as downstream
jet streaks attempt to couple, and at least some interaction with
a northern stream shortwave moving across southern Canada. The
overlap of these features will help drive cyclogenesis in the lee
of the Rockies, with this low intensifying as it shifts rapidly
northeast into Canada by Sunday aftn. Rich theta-e air surging
northward out of the Gulf of Mexico will aid in expanding
precipitation, and a large swath of heavy snow, sleet, and
freezing rain is likely. While there is still some uncertainty
into the location of the heaviest snow, there are likely to be two
areas of greatest accumulation. The first is in the upslope regime
into the Front Range of WY and along the Pine Ridge of NE where
WPC probabilities are greater than 50% for 6+ inches on D2. The
secondary maxima is likely within a strong deformation axis
progged to pivot from northern NE through SD, northern MN, and
into the western U.P. where WPC probabilities suggest a 30-50%
chance for 4+ inches, with some enhancement likely in the
Arrowhead of MN. East of the heavy snow, WAA will lead to more
mixed precipitation including freezing rain from near the Twin
Cities, MN through the U.P. of MI and WPC probabilities are again
high for 0.1" across this region. Event total freezing rain may
exceed 0.25" in parts of northern WI before the system winds down
to the east late D3.

Weiss