506
FOUS11 KWBC 031909
QPFHSD

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

Valid 00Z Fri Apr 04 2025 - 00Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1,2...

A deep upper level trough over much of the Intermountain West and
associated embedded upper level low over the Southwest will
gradually shift east onto the Plains through Saturday. Shortwave
disturbances moving around both the upper low and a secondary wave
moving along the Canadian border will provide the forcing for
wintry weather over and immediately downwind of those upper level
features.

For Day 1/Tonight through Friday, a potent trough over the Canadian
Prairies will dig southeastward into Montana and the Dakotas. This
will lead to pressure and height falls in the region. Troughing
developing as a response will draw a small portion of the Gulf
moisture plume into the northern Plains, supporting a widespread
generally light snowfall over Montana and the Dakotas. For the
mountains from the Bitterroots of Montana south to the Front Range
of Colorado, localized upslope along the terrain will cause much
heavier snowfall rates and amounts, especially in the Beartooths of
Montana and Bighorns of Wyoming, where new snowfall could approach
a foot through midday Friday. WPC probabilities are over 50% for 4
inches or more of snow for the Front Range of Colorado and the
Beartooths of Montana and Wyoming.

For Day 2/Friday Night and Saturday, the shortwave moving along the
Canadian border will shift east into the Great Lakes, leaving the
area. However, the upper level low/southern extension of the
broader upper trough will begin to tap ever-increasing amounts of
Gulf moisture as the lift ahead of the low moves in closer
proximity to the trough. This will draw more of that moisture
westward into the southern High Plains as the low-level jet
increases in both strength and amounts of Gulf moisture it will be
drawing northward into the nation`s mid-section. Upslope will play
an even greater role here, especially as the leeside surface trough
develops over eastern New Mexico. Some of the troughing from the
northern system from Day 1 in the northern Plains will propagate
straight southward along the Front Range and support the heavy
snow. The Sangre de Cristo Mountains of Colorado and New Mexico
will be the range hardest hit with heavy snow, with WPC
probabilities for over 8 inches of snow in the moderate-to-high
(50-70%) range through Saturday evening. The WPC Winter Storm
Severity Index (WSSI) shows areas along the state line near Raton
Mesa with major impacts from the large snowfall expected. The snow
will taper off in the area Saturday night.

...Northern New England...
Day 3...

A strong upper level trough over Hudson Bay Saturday will direct a
strong shortwave along its southeastern periphery towards New
England. Meanwhile, a portion of the moisture associated with the
excessive rainfall over the nation`s mid-section will draw
northeastward into the Northeast and New England. Here, that Gulf
moisture will interact with some lingering cold air over the
region, resulting in a variety of precipitation types over the
area. For areas south and west over northern New Hampshire and far
western Maine, a significant icing event is expected as warmer air
above freezing moves in aloft above the cold air in place,
resulting in precipitation changing over from snow to sleet and
freezing rain as the warm air moves in and deepens Saturday night.
There is a moderate-to-high (50-70%) chance of at least a tenth
(0.10") of an inch of ice across much of northern New Hampshire and
far western Maine near the New Hampshire border through Saturday
night, with a low (10-30%) chance of at least a quarter of an inch
of ice.

Further north where the warmer/above freezing air is unable to
reach, a light snowfall is expected, namely for far northern Maine,
where there is a low-to-moderate (30-50%) chance of at least an
inch of snow Saturday night. The moisture plume will shift east
with the cold front Sunday morning, ending the winter precipitation
threat.

Wegman

$$