Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 AM EDT Sun May 4 2025

Valid 12Z Sun May 04 2025 - 12Z Wed May 07 2025



...Intermountain West...
Days 1-3...

Stagnant but impressively amplified upper pattern characterized by
dual closed lows across the CONUS will result in increasing
precipitation beneath the slow moving vortex across the western
CONUS beginning today. The core of this low will emerge from the
Desert Southwest today before drifting slowly across the Four
Corners through Tuesday. On D3 /Tuesday into Wednesday/ a northern
stream impulse pushing a cold front southward will phase with the
larger gyre across the Four Corners bringing more widespread height
falls to the region, while also amplifying moist advection out of
the Gulf. This will lead to more impressive precipitation focused
across CO and northern NM, with snowfall occurring in the higher
terrain of the Front Range and Sangre de Cristos above generally
9000 ft. It is likely that the heaviest snowfall of the period
will occur D3 in this area as upslope flow combined with modest
fgen in the vicinity of the cold front and the large scale, but
broad, synoptic lift combine. This will result in heavy snow, for
which WPC probabilities suggest have a 70-90% chance of exceeding 8
inches in the Front Range and Sangre de Cristos, with 2-day
snowfall of 1-2 feet possible above 9000 ft. With periodic heavy
snow rates dragging down some colder air, especially in areas of
pronounced upslope, some light accumulations are possible in the
highest terrain of the Palmer Divide as well, impacting I-25.

Otherwise, during D1 and D2, heavy snow is likely across the San
Juans, generally above 10,000 ft, with more moderate snowfall
expected in the Sangre de Cristos (for the latter, this is separate
from the heavier snow D3). WPC probabilities across these areas are
high (>70%) for 6+ inches D1, and moderate (30-50%) D2.

Additionally, lighter snow accumulations are progged from the
Northern Rockies through the Absarokas and into the terrain around
Yellowstone NP, including the Wind River Range from D1 into D2
where WPC probabilities suggest there is a 30-50% chance for at
least 4 inches, and locally more than 8 inches is possible.

The probability of significant freezing rain across the CONUS is
less than 10%.


Weiss