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

Valid 12Z Fri Mar 21 2025 - 12Z Mon Mar 24 2025

...Northeast...
Day 1...

Low pressure near Cape Cod this morning will move through the Gulf
of Maine and into Nova Scotia this afternoon, helping to draw in
colder air on the back side of the exiting precipitation shield.
Rain will change to snow from west to east with some light
accumulation over most areas, but the higher terrain of the White
Mountains may see a few inches. There, WPC probabilities of at
least 4 inches of snow are 10-40%. In addition, there is a
possibility of some modest snow amounts over eastern Maine outside
the higher terrain as the low deepens in the Gulf of Maine this
afternoon. Snow will end by midnight over eastern Maine.


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

Onshore flow continues in the PacNW with a due east jet off the
northeast Pacific aimed into WA/OR. Current jet max along the
Columbia River will continue eastward this morning, but another
will be right on its heels which will promote a moisture plume into
the OR/WA Cascades this afternoon/evening. Snow levels around
3000-5000 ft will still impact the passes today. Snow will lessen
into day 2 (Sat) as height falls dig into the northern Rockies,
which will continue eastward into day 3. 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. Three-day totals of at least
12 inches of snow are likely (>70% chance) above 4000ft or so but
primarily on day 1.

West-to-east jet will continue to advance the moisture plume into
the northern Rockies, favoring the Blue, Sawtooth, Bitterroots,
Lewis Range, Absaroka, and Tetons through Saturday morning.
Elevations above 5,000ft in the Blue, Sawtooth, Bitterroots, and
Lewis Range have at least a 70% chance of receiving at least 12
inches of snow through tomorrow morning. Probabilities are a little
lower to the south (Absarokas and Tetons), but many areas will
still see at least 8 inches of snow (>70% chance above 7000ft or
so).

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...

Height falls associated with a shortwave exiting Montana Saturday
evening will continue to deepen into MN by Sunday morning in
response to the amplification of the upper pattern upstream. Low
pressure over SD will track eastward into MN with broad WAA ahead
of it over the Upper Midwest. Surface temperatures will be fairly
marginal with some areas starting as rain before mixing with and
changing to snow as the low strengthens on Sunday. As it does,
colder air will wrap around its northwest side over northern MN
moderate snow likely for a time Sunday afternoon. Models have been
wavering on the strength of the upper and sfc features (and thus
the QPF and ultimately the snow), but the eastern Arrowhead (Lake
Shore) may be in a favorable spot for heavier snow due to easterly
flow off Lake Superior. SLRs may start on the lower end below 10:1
then rise as colder air works its way in, but will also combat
afternoon solar insolation where rates are not as heavy. All told,
WPC probabilities for at least 4 inches of snow days 2-3 are at
least 10 percent generally north of I-94, with increasing
probabilities northward and northeastward into the Arrowhead. This
also includes northern WI into the U.P. of Michigan from a
combination of front-end WAA snow and wraparound snow after the low
passes through. Despite likely closing off up to 500mb, the system
will remain progressive but will not clear the area until after
12Z Mon.


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


Fracasso