Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
212 PM EDT Sat Mar 22 2025

Valid 00Z Sun Mar 23 2025 - 00Z Wed Mar 26 2025


...Pacific/Interior Northwest to Central Rockies...
Days 1-2...

Shortwave crossing MT/WY this evening will continue areas of high
elevation snow showers and favorable upslope conditions through
early Sunday morning in the Northern/Central Rockies until upper
ridging quickly builds into the West, while directing the next
Atmospheric River event into the Pacific Northwest through D2
(Monday). IVT is forecast to peak on Sunday evening and reach above
the 99th climatological percentile per the 00z NAEFS, with the
maximum corridor of 600-700 kg/m*s IVT directed at WA and the
northern Cascades as moisture also bleeds into northern ID/MT. As
expected, snow levels will quickly rise above 6000 ft and pass
level across the Northwest by D2 after starting out around 3000 ft
for the start of the event. High (>70%) WPC probabilities for at
least 8 inches of snow during the entire forecast period exist
across the WA Cascades and far northern ID/northwest MT ranges,
mainly above 5000-6000 ft.

Snell



...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

An upper-level trough exiting the Northern Rockies this afternoon
will track over Northern Plains and strengthen tonight, providing
modest vertical ascent aloft from the Dakotas to Minnesota. The
favorable synoptic-scale source of lift aloft will provide a
supportive environment for a deepening area of low pressure over
South Dakota. Increasing 850-700mb WAA and moisture advection in
advance of the storm's deepening 850mb will give rise to a
consolidated deformation axis late Sunday night over northern
Minnesota. Precipitation may briefly start out as an icy wintry mix
in parts of the Dakotas and northern Minnesota tonight and early
Sunday morning, but as strong vertical velocities manifest
themselves within the deformation zone, snow will become the
primary precipitation type across northern Minnesota. The heaviest
snowfall is likely to ensue along the Minnesota Arrowhead and
across the northern tier of Michigan's U.P.. Snowfall rates topping
1"/hr are most likely to unfold in these areas Sunday and into
Sunday night. Some of the latest guidance has come a bit farther
south on the storm track (closer to the EC-AIFS/UKMET/CMC solutions
but not completely in their camp), which has led to an increase in
snow over northern Wisconsin. CAA on the backside of the storm
system will keep lake-enhanced snowfall ongoing across northern
Wisconsin and the Michigan U.P. on east to the northern most
portion of Michigan's Mitten through Monday before concluding
Monday evening. WPC probabilities show moderate-to-high chances
(50-70%) for snowfall totals >8" in parts of the Minnesota
Arrowhead and the Michigan U.P.. There are also similar moderate-
to-high chances (50-70%) for snowfall >4" in northern Minnesota,
northern Wisconsin, and the northwestern Michigan Peninsula.

By Sunday night, the storm system's warm front will push into the
Northeast with low-level WAA and 290K isentropic ascent aloft. The
air-mass is marginally cold enough to support snow in the northern
Appalachians Sunday night, with the potential for a burst of heavy
snow in the White Mountains and much of interior Maine on Monday.
Guidance has remained split on whether a coastal low forms along
the Maine coastline, but should it form, locally heavy snowfall
totals (>6") could occur. At the moment, WPC probabilities show
low-to-moderate chances (30-50%) for snowfall totals >4" from the
White Mountains to northern Maine Sunday night and into Monday.
Westerlies over Lake Ontario may kick up a lake effect snow band
that becomes located over the Tug Hill on Tuesday. WPC
probabilities show moderate chances (40-60%) for snowfall totals
>4" in the Tug Hill on Tuesday.


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


Mullinax