FOUS11 KWBC 220807
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Fri Mar 22 2024

Valid 12Z Fri Mar 22 2024 - 12Z Mon Mar 25 2024

...Northern Rockies & High Plains, Central Rockies, Upper Midwest...
Days 2-3...

**Significant late season winter storm becoming increasingly likely
from the Northern Rockies and Northern High Plains to as far east
as the Upper Midwest this weekend

In wake of the storm system that tracked through the Upper Midwest
Thursday night, the large dome of high pressure over the Canadian
Prairies working in tandem with lower pressure in the West supports
a prolonged low-level easterly easterly flow regime into the
western Montana Rockies as well as central Montana and as far south
as the Absaroka and Big Horns. Another 700mb FGEN band will
strengthen throughout the day today and into Friday night as 700mb
WAA increases over the northern High Plains. In addition, much of
Montana lies beneath the divergent right-entrance region of a 100kt
250mb jet streak. This is a recipe for periods of snow today,
however snowfall rates will not come down heavily enough during the
day to do much more than Minor Impacts. Snow will accumulate more
effectively Friday night.

By Saturday morning, the approaching upper low in the Pacific
Northwest will spawn a new surface low somewhere over eastern Idaho
Saturday morning that will track into northern Wyoming Saturday
evening. The surface low will continue its trek southeast into
eastern Colorado, where NAEFS suggests it will eventually reach
MSLP values that are <0.5 climatological percentile. Meanwhile, the
850mb LLJ will accelerate over the Great Plains with winds topping
the 97.5 climatological percentile over the southern Great Plains
around 06-12Z Sunday. The LLJ will advect anomalous 850-700mb
moisture northward and wrap around the northern flank of the
strengthening surface low, and give rise to a blossoming shield of
heavy snow early Sunday morning from western Montana and northern
Wyoming to the Dakotas. Strong 850-700mb WAA and copious amounts of
Gulf of Mexico moisture will make its way into the Upper Midwest
where heavy snow will then ensue over southern Minnesota. By 00Z
Monday, a significant winter storm will be well underway, causing
strong winds and heavy snow from the Central Rockies on east
through the Black Hills, the Dakotas, and into the Upper
Mississippi Valley. NAEFS by 00Z Monday shows MSLP values in parts
of southwest Kansas and the TX/OK Panhandles that fall outside the
observed MSLP minimum for this time of year (~980mb), showcasing
the remarkable strength this storm will reach Sunday evening. By
early Monday morning, the storm will track northeast towards the
Missouri River with a pronounced TROWAL over the eastern Dakotas
and western Minnesota being the focus for the heaviest snowfall.

There remains some uncertainty in regards to the position and track
of the storm, but most ensemble members are on board with this
becoming an impressive late March winter storm. Latest WSSI-P shows moderate-to-high chances (50-80%) for Moderate Impacts from
eastern Montana and along the ND/SD border to south-central
Minnesota through early Monday morning. There are similar
probabilities for Moderate Impacts that stretch as far south as the
Sand Hills of northern Nebraska. There are even some low-to-
moderate chances (30-50%) for Major impacts in parts of eastern
South Dakota, southwest Minnesota, and throughout the Twin Cities
metro area. The primary drivers in the WSSI-P algorithm are Snow
Amount and Blowing Snow, the latter of which, shows >60% chances
for Minor Impacts as far south as the Palmer Divide and into
central Nebraska as a powerful cold front passes through these
areas on Sunday. There are more details on the event in the Key
Messages below, but residents in these areas are encouraged to
closely monitor the latest forecasts this weekend as this storm
will likely continue to cause hazardous impacts for parts of the
Northern Plains and Upper Midwest into the start of next week.


Mullinax


***Key Messages for Northern Plains Winter Storm***

--Significant winter storm likely

Confidence continues to increase in a large storm system that will
produce an area of heavy snow over the Northern Plains and into the
Upper Midwest, along with some areas of mixed precipitation this
weekend into early next week.

--Widespread heavy snow expected

Heavy snow is forecast to overspread eastern Montana late Saturday,
then expand into the Northern Plains and Upper Midwest by Sunday
afternoon. There is a high chance (>70%) of at least eight inches
of snow from the North Dakota/South Dakota border eastward into
Minnesota and northern Wisconsin.

--Hazardous impacts due to snow, snow load, and wind

A combination of heavy snow and gusty winds will likely produce
areas of blowing and drifting snow, as well as possible blizzard
conditions Sunday into Monday. Hazardous travel, along with some
disruptions and closures are expected late Saturday into Monday.
The combination of strong winds and heavy, wet snow on trees and
power lines may result in tree damage and power outages.

--Additional forecast changes anticipated

Uncertainty remains with precipitation type for southern-most areas
and a possible sharp northern snowfall gradient in northern-most
areas. Closely monitor the latest forecasts as the storm evolved
over the next 24-48 hours.

$$
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