811
FOUS11 KWBC 030740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Thu Apr 3 2025

Valid 12Z Thu Apr 03 2025 - 12Z Sun Apr 06 2025


...Northeast...
Days 1 & 3...

An icy wintry mix will continue from the White Mountains and
through much of interior Maine this morning as ongoing WAA and
intense 850mb FGEN sustains an icy setup over northern New England.
The lingering sub-freezing boundary layer will gradually erode as
the warm front advances northward with only northern Maine holding
on to any notable wintry mix through midday. WPC probabilities
depict low chances (10-30%) for additional ice accumulations >0.1"
in the White Mountains and western Maine through this morning.

Following a break in the action Thursday night through Saturday
morning, the next round of wintry mix arrives Saturday afternoon
as moisture from the Mississippi Valley streams northward into New
England. Similar to the Day 1 setup, low-mid level WAA and 850mb
FGEN are the primary mechanisms of lift that will promote
precipitation. The antecedent air-mass is not nearly as cold as the
Wed-Thurs air-mass. However, the modestly cold air-mass will be
tough to erode in the higher terrain, thus making the White
Mountains and western Maine the most likely areas to see a mix of
snow and freezing rain through Saturday night. WPC probabilities
show moderate- to- high chances (50-70%) for >0.1" of ice, with low
chances (10-30%) for ice accumulations >0.25".


...Intermountain West & Southern High Plains...
Days 1-3...

The weather pattern over the western third of the Lower 48 is
primarily driven by a pair of upper level disturbances; one
tracking across Montana today and early Friday, and the other is a
closed upper low over the Southwest. Starting in Montana, a cold
front at the leading edge of the 500mb shortwave trough will act as
a trigger for snow showers, some of which could have snow squall-
like impacts with bursts of snow and gusty winds Thursday
afternoon. With high pressure building in from Alberta, easterly
upslope flow into the Lewis Range and Absaroka through Thursday
evening. Snow associated with this upper trough is also expected as
far south as the Big Horns and even as far east as western North
Dakota Thursday night. By Friday morning, the cold front makes its
way south through the Central Plains and Central Rockies with
NErly upslope flow aiding in minor snow accumulations along the
Front Range of the WY/CO Rockies through Friday morning.

Farther south, the closed upper low will make its way toward New
Mexico with 200-500-700mb heights along the AZ/NM and Mexico
borders below the 10th climatological percentile. As the 700mb low
reaches western New Mexico Friday afternoon, winds over southeast
CO and northeast NM will turn easterly at the same time the
aforementioned cold front to the north plunges south. Southern CO
and northern NM will also be co-located beneath the divergent left-
exit region of a 500mb jet streak located over northern Mexico. The
heaviest snowfall looks to ensue Friday afternoon and into Friday
night across the Front Range, Palmer Divide, San Juans, and Sangre
De Cristo (including Raton Pass). By Saturday morning, snow is
forecast for most of the Southern Rockies and even parts of the
southern High Plains as the cold front continues to dive south and
the deformation zone on the northern and western periphery of the
700mb low moves in overhead. Note that with the time of year, it
will have to snow exceptionally hard (>1"/hr) for snow to
accumulate outside of the mountain ranges given the higher sun
angle and warmer soil temperatures. Still, periods of moderate snow
combined with 30-40 kt 850mb winds will cause poor visibilities
through Saturday afternoon before the snow finally tapers off
Saturday evenings.

WPC probabilities depict moderate-to-high chances (50-70%) for
snowfall >8" along the >9,000ft peaks of the Sangre De Cristo and
San Juans between Friday afternoon and Saturday afternoon. Along
the I-25 corridor, the most concerning area for heavy snowfall is
along Raton Pass where up to 12" of snow in the forecast. WSSI
depicts Moderate impact potential in the Sangre De Cristo, Raton
Mesa, and San Juans. Note that there are some Moderate Impacts in
the plains of eastern NM and the TX Panhandle with Blowing Snow the
primary impact in these areas.


Mullinax





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