FOUS11 KWBC 221903
QPFHSD
Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
203 PM EST Sat Nov 22 2025
Valid 00Z Sun Nov 23 2025 - 00Z Wed Nov 26 2025
...Southern Rockies...
Days 1-2...
An upper-low over Baja California will move northeast today and
tonight, spreading rain and high mountain snow across AZ then into
CO/NM tomorrow. Healthy subtropical moisture directed at the
Southern Rockies will at the same time be co-located beneath
diffluent flow aloft. Upslope enhancement into some of the
mountain ranges such as the Gila Mountains, the San Juans, and the
Sangre De Cristo will aid in producing periods of moderate-to-heavy
snow across these mountain ranges. The upper low will cross over
the Four Corners region on Sunday and deliver heavier snowfall to
the San Juans and Sangre de Cristos, but primarily in the
higher/remote elevations. Snow tapers off by Monday as the upper
low tracks into the central Great Plains.
Due to the lack of a cold antecedent air-mass, snow levels will
struggle to fall much lower than 7,000ft. Elevations above 9,000ft
in the Mogollon Rim and Gila Mountains and the more remote
elevations above 10,000ft in the San Juans and Sangre De Cristos
are the most likely candidates to see the heaviest snowfall amounts.
WPC probabilities for at least 8 inches of snow are >50% above
about 11,000ft in the more remote/higher ridge lines of the San
Juans and Sangre De Cristo range.
...Pacific Northwest & Northern Rockies...
Days 1-3...
A Pacific disturbance embedded within quasi-zonal flow will usher
in a progressive, but potent, frontal system into WA/OR/ID and
northwestern MT Sunday. As the cold front traverses the Pacific
Northwest, snow levels around 5000-6000ft Sunday afternoon will
drop to as low as 2,000ft on the windward side of the Cascades by
early Monday as precipitation begins to taper off. WPC
probabilities for >4" of snow do range between 40-60% in both
Stevens and Snoqualmie Passes, with potentially upwards of 6"
possible. A brief lull in mountain snow Monday night and into
Tuesday morning concludes by Tuesday afternoon when the next
Pacific storm system delivers another round of mountain snow to
the Cascades and Olympics with snow levels as low as 2,500ft.
Additional snowfall totals of 1-4" are possible through Tuesday
afternoon with more snow still to come into the middle of the week.
Farther east, snow will also spread across northern ID into
western MT late Sunday and through Monday as moisture associated
with the Pacific system passes through. Minor snowfall
accumulations (1-4") are possible as far south as the Tetons and
Big Horns. The focus for the heaviest snowfall resides along the
Lewis Range on Monday as snowfall rates become enhanced by
easterly upslope flow due to strengthening high pressure over
southwest Canada. Snow should taper off across all of the northern
Rockies by Early Tuesday morning. WPC probabilities for >8" of
snowfall are >70% across the Lewis Range above 5,000ft. In the
highest elevations of the Lewis Range (>6,000ft), WPC probabilities
show moderate chances (40-70%) for snowfall totals >12". The WSSI
does show mostly Minor Impacts in the Lewis Range, the Bitterroots,
the Crazy Mountains with some localized Moderate Impacts (hazardous
driving conditions) in the higher peaks of the Lewis Range.
...Northeast...
Day 2...
A clipper system rotating beneath the base of an broad upper-low
over Quebec will push quickly through northern NY/New England
Sunday afternoon/evening and exit to the east by Monday morning.
QPF and the resulting snowfall will be somewhat limited due to its
fast movement and the clipper being relatively moisture-starved,
but some upslope enhancement may allow for anywhere between 1-4"
of snow across the Tug Hill, Adirondacks, and both the Green and
northern White Mountains. WPC probabilities for at least 4 inches
of snow remain on the lower side (10-40%) in these areas generally
above 1500-2000ft in the Adirondacks and Tug Hill. Still, some
snow covered roads could make for slippery driving conditions
Sunday night and Monday morning.
...Northern Plains...
Day 3...
The shortwave trough responsible for the snow across the Northern
Rockies to start the week moves into the northern High Plains on
Monday night. There are ongoing differences on model guidance in
terms of the speed/strength of this feature as it enters the
northern High Plains. Most guidance does agree, however, that as
the 500mb trough tracks over the Dakotas, a compact 500mb low
develops and with an inverted low-to-mid level trough on the low's
western flank. This becomes effectively a TROWAL that helps to
focus a narrow band of 850-700mb FGEN and WAA that, when combined
with sufficient lef-texit region jet streak dynamics, gives rise to
a band of moderate-to-heavy snow starting over eastern MT Monday
night. As the 500mb low forms over the Dakotas on Tuesday, EC-AIFS
shows the TROWAL develops a formidable band of heavy snow over the
Dakotas Tuesday morning that then tracks into central MN by
Tuesday afternoon.
It is worth noting guidance over the last 12-24 hours is still
trying to synthesize a better forecast track with this developing
storm system, and the placement of where the heavier snowfall
occurs is still coming into focus. This is also looking like a
fairly progressive system, but could still pack a punch with
snowfall rates >1"/hr in play as it tracks through the northern
High Plains and Upper Midwest through Tuesday night. At this
moment, WPC probabilities are focusing on ND (20-50% chances for
4" of snow) as the most likely to witness impactful snowfall, as
well as gusty winds that greatly reduce visibilities. Heavy snow
will likely translate into northern MN by Tuesday evening, and SD
could also contend with wind blown snow that causes travel delays.
Interests in the Northern Plains and Upper Midwest should keep a
close eye on the forecasts from their NWS WFOs and WPC in the
coming days given this storm could prove a headache for those
traveling in the lead up to Thanksgiving.
The probability of significant ice across the CONUS is less than
10 percent.
Mullinax
$$
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