Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
443 PM EDT Wed Mar 26 2025

Valid 00Z Thu Mar 27 2025 - 00Z Sun Mar 30 2025


...West Coast through Northern Rockies...
Days 1-3...

An anomalously deep, cold-core low off OR near 140W will further
occlude and curl up toward Vancouver Island through Thursday night
with the occluded front crossing the West Coast tonight. High snow
levels (>8000ft) this afternoon will rapidly drop to around
4000-5000ft after midnight, then to around 3500ft Friday with the
passage of the upper trough axis. Accumulating will eventually
reach to some of the passes in the Cascades by Friday, but the
rates will drop around that time as well. So most of the heavy snow
will be in the higher elevations. Day 2 snow probs for >8" are
50-80% for the higher Cascades, Klamath, and northern Sierra
Nevada.

Moisture will continue inland through the northern Rockies Friday
through Saturday with periodic heavy snow above 5000ft snow levels
on Friday and 4000ft on Saturday. A focus for mountain snow remains
from the Blue Mtns of OR through SW MT (and the Bighorns of WY)
where Day 3 snow probs for >8" are 30-60%.


...Upper Midwest/Northern Great Lakes/Northeast...
Days 2-3...

Flattening upper ridging exiting the High Plains Thursday combined
with lee-side surface cyclogenesis centered over South Dakota
Thursday night will favor broad WAA-driven precipitation along and
north of a surface boundary draped over the Upper Midwest into the
Great Lakes. With the fast zonal/progressive flow, this will
quickly expand eastward through southern Canada and the Northeast
with through Friday night. Temperatures are marginal for most
areas, confining snow to areas closer to the Canadian border.
However, a sub-freezing surface layer will be overrun from the
S/SW with warmer air aloft, promoting a long, but narrow swath of
sleet/freezing rain from northern MN eastward across the U.P. of
Michigan and northern WI across Ontario, the Adirondacks, and
central New England. Ptype from the models (and NBM) show a strong
signal for freezing rain (impressive for late March), but this may
be initially modulated by Friday afternoon insolation before
focusing over the U.P. of MI Friday evening. Day 2.5 ice
probabilities for >0.25" have risen to 20-40% over much of the U.P.
and the far northern L.P. Day 2.5 snow probs for >4" are 30% up at
the top of the Arrowhead of MN, and 30-70% for Day 3 over the
northern Adirondacks, Greens, and Whites into western Maine.


...Northern Plains...
Day 3...

A shortwave trough axis that crosses the PacNW Friday reaches the
northern Rockies on Saturday promotes Colorado lee-side low
development on Saturday. Broad convergence should allow some
moderate to locally heavy snow bands to form around SD into MN
by Saturday afternoon. The 12Z GFS/EC have come into better
agreement, though the EC remains a bit more progressive. Will need
to monitor the threat for heavy fgen snow banding over portions of
the northern Plains into Upper Midwest Saturday/night.



Jackson