Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Sun Apr 13 2025

Valid 00Z Mon Apr 14 2025 - 00Z Thu Apr 17 2025


...Colorado Rockies...
Day 1...

Shortwave will move from UT to CO tonight and help wring out some
snow for the high Rockies and lighter snow below 7500ft as colder
air comes into CO by Monday. WPC probabilities for at least 6
inches of snow after 00Z tonight are moderate (40-70%) across a
narrow region of the northern CO Rockies along the Front Range
(above 10,000ft) just west of Boulder.


...Western Great Lakes...
Days 1-2...

The mid-level low exiting MT today will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure at the tip of this jet will deepen over
northern WI and help foster an expanding area of precipitation
throughout the region. Temperatures will be mild initially (upper
50s into central MN/WI), but once the low tracks into Lake
Superior, north to northwest winds will rapidly bring in colder air
to northern areas of MN and eventually into the U.P. of Michigan
Monday night into early Tuesday. Rain will change to snow and
become more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. and northern Lower
Michigan. By Tuesday, with the surface low well into Ontario,
northerly winds will advect in 850mb temperatures of around below
negative 6C which may be enough to spur some lake enhancement
(Lake Superior temperatures around 4-5C). The snow will end from
west to east on Tuesday. WPC probabilities for at least 6 inches
of snow through 00Z Wed are moderate (30-50%) in northeastern MN.
For areas downwind of Lake Superior (far northern WI through the
U.P. of Michigan), higher amounts are likely Monday night through
Tuesday, with WPC probabilities depicting 20-60% chances for at
least 8 inches of snow in the favored areas just inland from the
lake shore and with any elevation (e.g., Porcupine and Huron
Mountains). For northern Lower MI, WPC probabilities for at least 4
inches of snow are low (10-30%).


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

Low pressure will continue through Canada with its cold front
rushing across the Northeast on Tuesday. Behind it, colder air will
filter in with lingering precipitation downwind of the eastern
Great Lakes with some upslope in the central Appalachians as well.
Temperatures will be marginal for some lower elevations and also
near the lake waters, but light to moderate accumulation is likely
over much of western and northern NY (Chautauqua Ridge, Tug Hill
Plateau, Adirondacks). WPC probabilities for at least 4 inches of
snow are 10-30% in far western WY, with highest chances (50-80%) in
the Adirondacks and Tug Hill Plateau.


...Northwest Montana...
Day 3...

Active and wintry weather returns to northwest MT by the end of D3
and is expected to expand further into much of the Intermountain
West/Rockies on D4. Deepening upper troughing is forecast to
develop over the West anchored by a meandering upper low
approaching southern CA on Wednesday. Meanwhile, a sharp shortwave
diving southward from British Columbia into northern WA/ID by
Wednesday evening will help start the event. Behind a cold front
racing southward across northwest MT, ample lift underneath a
strengthening mid-level low combined with upslope flow along the
Lewis Range could support locally heavy snowfall on Wednesday.
Here, WPC probabilities through 00Z Thursday are currently 30-50%
for at least 4 inches of snowfall, but should increase once the
entire event enters the forecast period.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Snell