Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
223 PM EDT Fri Mar 21 2025

Valid 00Z Sat Mar 22 2025 - 00Z Tue Mar 25 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-3...

Onshore flow continues in the PacNW through early next week with
two primary waves of moisture traversing the region with upper
ridging expected to cut off Pacific moisture tap by late D3. For D1
(through 00z Sun), snow levels will drop below 3000 ft across the
Northwest, but also as precipitation quickly dries out and the
focus of upper divergence shifts into the Northern Rockies through
the beginning of D2. Here, snow levels around will start out around
4000-5000 ft but also fall below 3000 ft due to approaching height
falls. By then, upper ridging will move into the PacNW with a
system into the southern AK Panhandle, allowing snow levels to rise
much higher to above 6000ft Sunday afternoon into early Monday as
the next moisture plume clips the Northwest and northern Great
Basin. Totals of at least 12 inches of snow are likely (>70%
chance) above 4000ft or so but primarily on day 1 throughout the
Cascades, Sawtooths, northern ID ranges and western MT ranges, as
well as the Absarokas and Wind River Range of WY. By D2-D3 high
probabilities for at least 6 inches of snow remains confined to the
northern WA Cascades and far northern ID ranges.

On the south side of the jet and moisture plume, northern UT into
the CO Rockies will likely see at least 8 inches of snow above
9000ft or so (>70% chance), starting later tonight into Saturday
then ending Saturday night.


...Upper Midwest & Great Lakes...
Days 2-3...

An upper-level trough exiting the Northern Rockies Saturday
afternoon will track over the Northern Plains and strengthen
Saturday night, providing modest vertical ascent aloft from the
Dakotas to Minnesota. The favorable synoptic-scale source of lift
aloft will provide a favorable environment for a deepening area of
low pressure over South Dakota that will, in turn, generate
increasing 850-700mb WAA in advance of the storm. By Saturday
night, a consolidating 850mb low over the Red River of the North
will wrap modest low-mid level moisture around the northern and
western flanks of the low. As precipitation breaks out from central
North Dakota to as far east as northwest Wisconsin Saturday night,
some precipitation may start out initially as an icy wintry mix.
But as the deformation axis becomes more pronounced, dynamic
cooling aloft will allow for snow to become the primary
precipitation type through Sunday morning. Gusty winds on the
backside of the storm will prompt blowing and rifting snow to ensue
across the Dakota and into northwest Minnesota through Sunday
morning.

The region most likely to witness the heaviest snowfall for this
event is northeast Minnesota or, more specifically, the Minnesota
Arrowhead. The deformation axis is expected to pivot over the
region on Sunday with sufficient vertical velocities throughout
much of the atmospheric column to support heavy snowfall rates
>1"/hr, while the Arrowhead, contending with easterlies off of Lake
Superior, provides a lake-enhanced fetch of moisture into the
region Sunday afternoon and into Sunday night. Meanwhile, farther
east, the Michigan U.P., especially the Keweenaw Peninsula on east
to the Hurons and just west of Sault Ste. Marie, the strong WAA
north of the warm front will be sufficient enough to produce a
burst of heavy snow Sunday afternoon and into the evening hours.
This area is a little more unclear on the SLR's and snowfall rates
as there is some evidence of a potential dry slot within the
700-300mb layer working its way in, but there will still be snow to
contend with on the back side of the storm Sunday night. The storm
will work its way over Michigan's U.P. Sunday night with CAA on
the western flank kicking up lake- enhanced snow showers in its
wake across northern Wisconsin and much of the Michigan U.P.. Snow
should finally taper off by Monday afternoon as winds diminish and
lingering lake effect snow showers over the eastern Michigan U.P.
and the tip of Michigan's Mitten wind down.

WPC probabilities show moderate-to-high chances (50-70%) for
snowfall totals >8" along the Minnesota Arrowhead, with similar
probabilities for >6" in northeast Minnesota and in the Michigan
U.P.. Note that there are moderate chances (40-60%) for >4" of
snow as far west as northwest Minnesota and as far south as
northern Wisconsin. Expect hazardous travel conditions in these
areas on Sunday with poor travel conditions lingering over Michigan
U.P.


...Northeast...
Day 3...

As the Upper Midwest and Great Lakes system slides east by D3, a
brief period of moderate snowfall is possible across northern New
England and elevated regions of the Interior Northeast. Mid-level
WAA will be the driving force behind the precipitation pushing
eastward on Monday, with a triple-point surface low developing near
southern New England also providing for potential weak CAD across
parts of ME and NH. WPC probabilities for at least 4 inches of snow
are currently low (10-30%) from the Adirondacks to Green/White Mts
of New England, with slightly higher probabilities in the highest
elevations.


For days 1-3, the probability of significant icing of at least
0.10" is less than 10 percent across the CONUS.


Snell/Mullinax