Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
435 PM EDT Thu Apr 25 2024

Valid 00Z Fri Apr 26 2024 - 00Z Mon Apr 29 2024


...The West...
Days 1-3...


A series of impulses approaching the PacNW dig southeast tonight to
Friday, which builds a substantial longwave trough over the Great
Basin. This trough then shifts east, closing into a low over the
Four Corners early Saturday before swinging northeast through CO
through Saturday night and into the Dakotas Sunday. Pacific
moisture streaming in ahead of this trough makes for a broad areas
of higher elevation snow to develop across much of the
Intermountain West on Friday. Day 1 PWPF for >6" are 50-90% over
the OR Cascades which sees the most direct lift of Pacific
moisture as this trough crosses tonight (with snow levels dropping
from 6000ft to 5000ft), and generally 40-80% above snow levels of
6000-8000ft over the higher Great Basin ranges in NV and UT as
well as the Absarokas and Wind Rivers.

As the developing low shifts east over the Four Corners Friday
night, the heavy snow focus shifts to the Rockies from CO through
southwest MT. Lee- side cyclogenesis downstream of the low develops
over southeast CO late Friday which focuses flow of Gulf moisture
into the north- central Rockies which provides additional ascent
through upslope flow and periods of enhanced fgen, potentially
overlapping a deformation axis in the Central Rockies, to produce
heavier snowfall rates exceeding 1"/hr at times. Snow levels in the
Rockies will remain generally elevated, primarily 8000 ft, but
with steepened lapse rates beneath the cold trough and some areas
of enhanced ascent, snow is possible into the 6000ft elevation
range. Day 2 PWPF for >8" is 50-90% over the Wind Rivers, Front
Range, and portions of the San Juans and more like 30-70% for the
rest of the higher terrain between southwest MT, UT, and central
CO. The pivot to a northeast direction over CO late Saturday makes
a potential for persistent banding and substantial snowfall at
elevation with 2-3ft likely in the higher terrain of the Wind
Rivers and Front Range.

The low shifts onto the Plains Sunday with a deformation axis
possibly bringing accumulating snow to the High Plains and a
notable reduction in rates and coverage to the Rockies. PWPF for
>4" is generally 40-70% over the CO Rockies into southern WY.

The next low tracks from the southern Gulf of Alaska Saturday night
bringing moderate precip to the PacNW with snow levels around
4000ft. Day 3 PWPF for >4" is 30-80% in the North Cascades of WA.



The probability of significant icing is less than 10 percent.


Jackson