Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Mar 26 2024

Valid 12Z Tue Mar 26 2024 - 12Z Fri Mar 29 2024

...Upper Midwest...
Day 1...

The major winter storm that has produced heavy snow, blizzard
conditions, gusty winds, and in some areas an icy wintry mix is in
its final day of producing hazardous impacts across the Upper
Midwest. The storm is currently working its way northeast through
the Upper Mississippi Valley with its deformation axis on the
western flank of the storm producing heavy snow in central and
northern Minnesota. Meanwhile, an icy wintry mix will linger in
parts of eastern Minnesota, northern Wisconsin, and along the
Minnesota Arrowhead early this morning before flipping back over
to snow as the storm tracks northeast. Much of Minnesota can expect
periods of snow and gusty winds causing reduced visibilities and
blowing snow through Tuesday afternoon. As the storm tracks over
Lake Superior and into southern Ontario Tuesday evening, snow will
gradually wind down over northern Minnesota but lingering wind
gusts topping 30 mph may still cause some blowing and drifting
snow. WPC PWPF shows moderate chances (40-60%) for additional
snowfall totals >4" from the Minnesota Arrowhead to as far south
as the Twin Cities metro area. High pressure finally builds in late
Tuesday night and into Wednesday, effectively ending this late
season winter storm in the Upper Midwest.

...Pacific Northwest, Northern California, & Northern Rockies...
Days 1-3...

Modest Pacific moisture streaming in amidst broad northwesterly
flow will result in heavy snow for some of the tallest peaks of
the Cascades, the Blue Mountains, the Bitterroots, and Lewis Range
through Tuesday. For elevations >6,000ft, WPC PWPF shows moderate-
to-high chances (50-70%) for snowfall totals >4" through early
Wednesday morning. By Wednesday morning, the next Pacific storm
system is slated to bring the next slug of Pacific moisture into
the Pacific Northwest and Northern California beginning Saturday
afternoon. The IVT associated with this storm system is a potent
one (ranging between 300-400 kg/m/s, topping out around the 97.5
climatological percentile), but it is on the progressive side. The
IVT supplies not only plenty of moisture for mountain ranges to
work with, but also sufficient upslope flow to further enhance
precipitation rates. Snow levels will initially start out around
6,500ft in the Sierra Nevada Wednesday afternoon, but as the cold
front pushes through and upslope enhancement transpires, snow
levels originally >6,000ft will drop to <5,000ft by Thursday
morning. Farther north, snow levels in the Olympics and Cascades
will hover around 5,000ft initially, then drop to <4,000ft by
Thursday morning.

While the IVT will weaken and push inland on Thursday, the
lingering upper low off the Pacific Northwest coast will continue
to funnel additional Pacific moisture into the Pacific Northwest
that will stream as far inland as the Northern Rockies and as far
south as the Uinta and Wasatch. By Thursday night, a secondary
500mb vort max will track south and lead to a resurgence in the
IVT, but this time into central California and the central Great
Basin for Friday. The Sierra Nevada will once again see another
round of heavy snow Friday afternoon that is likely to linger into
Saturday. Portions of the Salmon/Trinity/Siskiyou are also likely
to receive heavy snow into the first half of the upcoming weekend.

WPC PWPF sports high chances (>70%) for snowfall totals >8" in the
northern Sierra Nevada, the Salmon/Trinity/Siskiyou of Northern
California, the Olympics, and some of the volcanic peaks of the
OR/WA Cascades on Wednesday. WPC WSSI-P shows >60% chances for
Moderate Impacts in portions of these mountain ranges between
Wednesday afternoon and Thursday morning. Thursday is the day
between Pacific storm systems, but the lingering onshore flow does
provide low-to-moderate chances (30-50%) for >6" of snowfall in
the Sierra Nevada, the Northern California ranges, and parts of the
Olympics and Cascades. Meanwhile, the first IVT plume will bring
about mountain snow as far inland as the Sawtooth, the Absaroka,
and the Tetons. Between 00Z Wednesday - 00Z Thursday, WPC PWPF
depicted moderate-to-high chances (>70%) for snowfall totals >8"
in portions of these mountain ranges.

Mullinax