Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
436 AM EDT Wed Apr 16 2025

Valid 12Z Wed Apr 16 2025 - 12Z Sat Apr 19 2025


...Interior Northeast...
Days 1...

A departing upper low will bring continued snow showers to the
interior northeast today and this evening, winding down by later
tonight. One more reinforcing piece of shortwave energy diving
into New England should support an uptick in snow shower activity
this afternoon, and while snow may fall even into lower elevations,
most of the accumulation will stay in the favored terrain
generally above 1500 feet. These higher terrain areas of VT and NH
could pick up an additional 2-6" of snow today into this evening.

...Northern/Central Rockies...
Days 1-3...

There has been little change in the forecast synoptic pattern that
will yield some impressive snowfall totals across the Northern and
Central Rockies into the Inter-Mountain west. A longwave trough and
embedded closed low will dive south southeast across the region,
with colder air filtering in behind a cold frontal passage.
Northeasterly upslope flow behind the front, combined with ample
large scale lift associated with the trough/closed low, will drive
a heavy snowfall threat across the region. Snowfall will initially
focus across the Lewis and Flathead ranges of northwest MT today
and will likely be heavy at times, with rates exceeding 1"/hr. WPC
probabilities highlight a high chance (>70%) of exceeding 8" of
snow in the favored east facing terrain generally above 4500 feet.

By Wednesday night the snow risk shifts into southern MT, with the
heaviest accumulations expected above 4000 feet. Above this
elevation there is a high chance (>70%) of exceeding a foot of
snow, and localized totals could approach two feet in the highest
terrain areas. The forecast remains less confident over the lower
elevations of southeast MT. Thermal profiles will be marginal, but
the overnight timing and moderate to heavy rates, should be enough
to change rain to an accumulating snow. Just how much accumulation
remains to be seen, but amounts did trend up this cycle, with 4"
exceedance probabilities increasing into the 30-50% range for
Billings and surrounding lower elevation areas. The greatest bust
potential for this forecast is probably over the lower elevations
of southern MT and we could see amounts continue to trend up. The
potential for stronger banding during the overnight hours does
suggest there is at least some potential for snowfall to
overperform across these areas, so will need to to continue to
monitor.

By Thursday the heavy snow is overspreading WY with the greatest
accumulations again focusing across the favored
higher terrain...such as the Absaroka Range, Bighorn Mountains,
Wind River Range, Laramie Mountains, Medicine Bow Mountains and the
Sierra Madre. All of these areas have at least a 50% chance of
exceeding 12 inches of snow with this system. With the colder air
filtering in snow is also likely across the lower elevations, with
forecast snow amounts increasing this cycle across much of central
to southeast WY. The probability of exceeding 4" of snow has
increased into the 50-80% range over much of these lower elevation
areas across this part of the state.

By Thursday night into Friday the snow shifts southward into CO.
With marginal boundary layer temperatures the better accumulations
will likely be confined to elevations above 6000 feet, where
probabilities of exceeding 8" are over 70%. A bit more
uncertainty as you drop into the Front Range and foothills of the
Rockies. We do expect some accumulation to get into these
relatively lower elevations, but marginal boundary layer
temperatures will probably cut into snow ratios. Another negative
factor for higher accumulations in these areas is the fact that the
peak of the event is during daytime hours Fri...thus given the
high sun angle and borderline temperatures...it will likely take
heavier rates to get any efficient accumulation. Nonetheless, WPC
probabilities show a 50-80% chance of exceeding 2" and a 20-50%
chance of exceeding 4" over these areas.


...Central Sierra and Central UT...
Days 1-3...

Elsewhere, high (>70%) probabilities of exceeding 6" of snow
exists across the higher elevations (generally above 8000 feet) of
central UT. This snow will be associated with a southward dropping
cold front Thursday into early Friday, and should be accompanied
by pretty high snowfall rates.

Snow showers are likely today above 8000 feet across the Sierra of
central CA, with a 50-70% chance of seeing some areas exceed 4".

Chenard