FOUS11 KWBC 280650
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
249 AM EDT Thu Sep 28 2023

Valid 12Z Thu Sep 28 2023 - 12Z Sun Oct 01 2023

...California/High Sierra Nevada...
Day 3...

A reinforcing shortwave trough digs around low pressure over
Vancouver Island, amplifying into a closed low over the northern
CA/NV border Saturday night. A plume of Pacific moisture shifts
into central CA Saturday is lifted over the Sierra Nevada. Snow
levels look to be around 8000ft per the NBM with moderately high
Day 3 WWD probabilities for 4 or more inches over the High Sierra
as well as the highest White Mtns.


The probability of any ice accumulation across the CONUS is less
than 10 percent.


Jackson


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FOUS11 KWBC 290749
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Sep 29 2023

Valid 12Z Fri Sep 29 2023 - 12Z Mon Oct 02 2023

...Sierra Nevada through the Northern Rockies...
Days 2-3...

A shortwave trough currently off the southern OR coast amplifies
as it digs south down the California coast through tonight before
closing into a low pressure system along the northern CA/NV border
Saturday night with little movement expected then through Sunday.
A plume of Pacific moisture streams into central/southern CA
tonight with precip spreading over the Sierra Nevada late tonight
and the Great Basin Saturday into Sunday. This anomalous low will
drive snow levels down to around 9000 ft during the heavier precip
Saturday through Sunday in the Sierra Nevada, the Great Basin
ranges, and the Northern Rockies. WPC probabilities for over 4" of
snow peak around 40% in the High Sierra on Day 2. This will likely
produce at least minor impacts at the highest passes including
Tioga Pass. As the precip spreads across the Great Basin to
northern Rockies Sunday, moderate snow is likely on the highest
ranges, though the Day 3 WPC probabilities for over 4" are
negligible.


The probability of any ice accumulation across the CONUS is less
than 10 percent.


Jackson

$$
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FOUS11 KWBC 010749
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
349 AM EDT Sun Oct 01 2023

Valid 12Z Sun Oct 01 2023 - 12Z Wed Oct 04 2023

...Sierra Nevada and White Mountains...
Day 1...

An upper low over southern Nevada lifts over Utah this morning
while a reinforcing trough currently near the OR/CA coastal border
shifts down the CA coast today closing over SoCal this afternoon.
Showers develop over the Sierra Nevada this afternoon from
instability under the upper trough (snow levels generally around
8500ft) with a northeasterly flow developing from surface low
pressure intensifying over southern NV. Day 1 snow probabilities
are moderately high for 4"+ over the High Sierra and the White
Mtns.


...Utah through the Northern Rockies...
Days 1-3...

The low lifting over western Utah this morning sends moderate
precip on a southerly flow over the Wasatch and Uintas today with
snow levels around 9000ft. Day 1 WPC snow probs are moderately
high for 6"+ for the Uintas with the highest Wasatch on a similar
scale. The reinforcing low from the CA coast today and up western
UT late tonight into Monday sends another round of moderate precip
through northern UT and western WY with snow levels dropping to
around 8500ft with Day 2 snow probs moderate for 6"+ over the
Uintas and Wind River with moderate snow over the
Tetons/Absarokas/Bighorns.

Continued troughing over the northern Rockies makes for light to
locally moderate precip with snow levels around 8000ft Tuesday.



The probability of any ice accumulation across the Continental
U.S. is less than 10 percent.

Jackson

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FOUS11 KWBC 020740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Mon Oct 02 2023

Valid 12Z Mon Oct 02 2023 - 12Z Thu Oct 05 2023

...Utah through Western Wyoming...
Days 1-2...

The next wave rounding the positively-tilted upper trough axis
extending from western MT through southern CA is over the NV/AZ
border early this morning and will track NNE over western UT to
western WY today. This track is a bit west of the one from
yesterday morning and the southerly flow east of this wave will
again cross over the Wasatch and Uintas and bring moderate precip
with with snow levels dropping to around 8500ft. An additional
6-10" across this highest terrain is expected today. The moist
southerly flow causes like to moderate precip over the ranges of
western WY through tonight with snow levels generally around
9000ft. The Day 1.5 WPC snow probs are moderate for 6"+ over the
Wind River and Absarokas.

The trough axis ejects east Monday night, bringing an end to
precip through this corridor from UT through WY which only light
snow persisting into Tuesday.

Elsewhere, an atmospheric river pushing over the Pacific Northwest
today is much more potent with precip than previously progged, but
as it most ARs, the snow level is high over the WA/OR Cascades -
generally around 10,000ft.

Ridging then builds over the western U.S. Tuesday into Friday,
making for a quiet stretch precip-wise over the western U.S. later
this week/through the weekend.


The probability of any ice accumulation across the Continental
U.S. is less than 10 percent.

Jackson

$$
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FOUS11 KWBC 030811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Tue Oct 03 2023

Valid 12Z Tue Oct 03 2023 - 12Z Fri Oct 06 2023

...Wyoming Rockies...
Day 1...

The upper trough remnant that was a Great Basin low on Monday will
continue to lift northeast from central WY today. Light to locally
moderate precip will continue today with flow becoming westerly
over the WY Rockies. Snow levels dip to around 8000ft this morning
then rise to around 8500ft this afternoon before precip tapers off
with height rises from the approaching upper trough. Day 1 snow
probabilities for additional accumulations after 12Z are 20 to 40
percent for 4"+ for the higher Absarokas (including the Red
Lodge/Beartooth area in MT), Tetons, Wind River, and Bighorns,
with a localized risk for 8" max.

A warm ridge builds over the West into Friday and persists through
the weekend, bringing an end to this early season wintry weather
(and likely melting all but the highest fresh snow packs.


The probability of any ice accumulation across the Continental
U.S. is less than 10 percent.

Jackson

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FOUS11 KWBC 090847
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
445 AM EDT Mon Oct 09 2023

Valid 12Z Mon Oct 09 2023 - 12Z Thu Oct 12 2023

For Days 1-2, the probability of significant snow or ice
accumulation across the contiguous U.S. is less than 10 percent.

...Day 3...
Northern Rockies...

A mid-upper level trough will move from the Pacific Northwest
Tuesday night to the central/northern Rockies by Wednesday night.
Meanwhile, a near 110-kt jet positions itself across Nevada/Utah,
putting portions of the Intermountain West to Northern Rockies in
the favored left-exit region. A front crossing the region will
bring colder air with 700 mb temperatures falling below 0C,
lowering snow levels initially from 9000+ ft to around 7000-7500
ft. By early Thursday, as the core of the upper low settles over
the region, the colder temps combined with a lingering surface
trough will enhance precipitation, particularly across portions of
WY. WPC probabilities for Day 3 (12Z Wed-12Z Thu) for at least 4
inches are between 10-40 percent for portions of the Colorado
Rockies, the Utah Unitas, and portions of the Snake River region
and southwest Montana mountains. Probabilities for at least 4
inches are highest (40-70+ percent) for western Wyoming ranges
including Tetons, Wind River, and the Big Horns with the greatest
probabilities above 8500-9000 ft where probabilities for at least
8 inches are 10-20 percent.

Taylor

$$
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FOUS11 KWBC 100848
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
448 AM EDT Tue Oct 10 2023

Valid 12Z Tue Oct 10 2023 - 12Z Fri Oct 13 2023

...Pacific Northwest...
Days 1-2...

Mid-upper level troughing moves onshore the Pacific Northwest
through today and tonight and the favored left exit region of the
110+ kt jet will provide plenty of forcing for ascent across the
region. Snow levels will gradually drop through this morning to
under 6000 ft before rising again later today to around 6500 ft.
This will really limit the greatest snowfall accumulations to the
highest peaks of the Cascades where WPC snow probabilities for at
least 4 inches are high. By late tonight into Wednesday, the core
of the upper level low moves overhead and snow levels fall back
toward 6000 ft.


...North-Central Rockies...
Days 2-3...

Strong mid-upper level trough moves through the Intermountain West
and Rockies later Wednesday into Thursday, eventually closing off
in the lee of the Rockies early Thursday. Favorable forcing for
ascent, aided by the left exit region of the upper jet streak,
combined with the orographic upslope, will bring widespread
precipitation to the North-Central Rockies. As a cold front sweeps
eastward, snow levels will fall from around 9000 ft to 7000 ft,
leading to greater snowfall accumulations for the higher peaks.
Meanwhile, a strong surface low is expected to develop in the lee
of the Rockies, with greater frontogenesis and orographic upslope
across portions of the CO Rockies northward into Wyoming and SD
Black Hills. This will enhance precipitation, particularly across
WY. The WPC probabilities for at least 8 inches are moderate
(40-60 percent) for the northern CO Rockies, through WY, and into
south-central MT ranges. The Big Horns have above 50 percent
probabilities for at least 12 inches. This is shaping up to be a
potentially significant early season event for some locations,
with the WSSI-P showing 40-60 percent probabilities for moderate
impacts across the WY mountains and SD Black Hills, driven
primarily by the snow rate and snow load, which makes sense given
the high moisture present with this system. It's possible by the
end of Day 3 (Thursday night), as the core of the upper level low
moves into the High Plains, wet snow may reach the lower
elevations of the eastern Wyoming and western Nebraska.


Days 1-3, the probability of significant ice accumulation across
the contiguous U.S. is less than 10 percent.

Taylor

$$
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FOUS11 KWBC 110825
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Wed Oct 11 2023

Valid 12Z Wed Oct 11 2023 - 12Z Sat Oct 14 2023

...Washington & Oregon Cascades...
Day 1...

A cold front sweeping through western Washington and Oregon early
this morning along with the core of the mid-upper level low moving
onshore will continue to bring unsettled weather and widespread
precipitation to the region through the rest of today and tonight.
The impressive moisture plume and westerly flow resulting in
favored upslope will contribute to some hefty precipitation totals
but the relatively higher snow levels (6000+ ft) will mainly
confine the greatest snowfall accumulations to the highest peaks
of the Oregon and Washington Cascades where additional
accumulations of several inches to localized 1-2 ft are expected.


...North Central Rockies & Black Hills...
Days 1-2..

The upper trough responsible for the heavy snowfall in the
Cascades will also be responsible for the first significant winter
storm of the season in the North Central Rockies. The first round
of precipitation will begin later today with greater height falls
and a steady stream of moisture traversing from south-central
Montana southward toward northern Utah and the Colorado Rockies.
The moisture anomalies and strong forcing for ascent will result
in periods of moderate to heavy snow through Thursday morning, as
the colder temps aloft pour in and the upper level low settles
overhead. At this point, the model consensus is for a deepening
area of low pressure to develop in the lee of the Rockies,
wrapping significant amounts of moisture around the northwest side
of the 700 mb low, leading to a robust deformation band of
precipitation aided by favorable upslope flow. This should
generate some impressive early-season snowfall totals for the
higher elevations of the Absaroka, Wind River, Bighorn, Laramie,
and northern Colorado Rockies ranges between 00Z Thurs - 00Z Fri
where WPC probabilities for at least 8" remain 50-90 percent. In
the Black Hills, there is slightly less confidence (30-40 percent
for at least 8") but still some members in the WSE that show some
significant totals. In the lower elevations, snowfall
accumulations (potentially 1-4") will be driven by snow rate as
boundary layer temperatures are marginal.

Impacts-wise, the WSSI-P shows probabilities of 60-80% of Moderate
Impacts in the Bighorns and Laramie Mountains more specifically,
with around 30% probabilities also depicted in the Black Hills and
Wind River Range. This in turn could mean treacherous travel and
hazardous conditions for outdoor activities in these areas
Thursday and into early Friday. In western Nebraska and southwest
South Dakota, strong wind gusts combined with periods of snow
would result in reduced visibilities. This is accounted for in the
WSSI which depicts Moderate impacts are possible from the Laramie
Range on east to western Nebraska on Thursday.


Days 1-3, the probability of significant ice accumulation across
the contiguous U.S. is less than 10 percent.

Mullinax/Taylor

$$
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FOUS11 KWBC 120758
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Thu Oct 12 2023

Valid 12Z Thu Oct 12 2023 - 12Z Sun Oct 15 2023

...North Central Rockies into the Black Hills...
Day 1...

A robust winter storm continues to take shape across the northern
Rockies this morning as a narrow upper jet pushes through the Four
Corners region. Snow will continue over the WY mountains through
the day with significant accumulations. In the mid-levels, the
newly closed off 500mb trough will swing across northern CO and
move into the NE Panhandle this evening as surface low pressure
lifts northeastward into and across central NE. As the upper jet
rounds out across CO and punches northeastward, strong upper
divergence will foster lift through the column in tandem with
cooling in the whole layer over eastern WY into the Black Hills of
SD as well as northwestern NE. Strong moisture flux into the
region from the south will wrap around and into the low via the
WCB which should enhance snowfall as temperatures cool to near and
just below freezing overnight into early Friday. Hi-res guidance
shows potential for several inches of snow into the NE Panhandle,
aided by falling overnight, with more intense rates overcoming
mild ground temperatures.

Snowfall will be generous over the terrain in WY, with an
additional foot likely (probabilities >50%) after 12Z today for
the Bighorns, Absarokas, Laramie Mountains, and Wind River Range.
To the east, temperatures will continue to fall during the day and
especially after dark over southwestern SD and northwestern NE.
Over the Black Hills, WPC probabilities for at least 4 inches of
snow are high (>70%) but are much lower over the NE Panhandle
where there is more uncertainty in accumulation. However,
probabilities for at least 2 inches are >50% there with a higher
end potential of a few times that. Impacts via the WSSI are driven
by snow load (highest over the Black Hills) and Blowing Snow with
strong winds tonight in eastern WY to western SD/NE.


Days 2-3...
The probability of significant snowfall is less than 10 percent.

For days 1-3, the probability of significant ice accumulation
across the contiguous U.S. is less than 10 percent.

Fracasso

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