FOUS11 KWBC 020626
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Thu Oct 2 2025

Valid 12Z Thu Oct 02 2025 - 12Z Sun Oct 05 2025

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

An upper low over the Great Basin on Friday opens into a trough and
shifts east over the Rockies late Saturday. Lee-side cyclogenesis
over western South Dakota occurs during this time enhancing flow
from Gulf-sourced moisture over the Plains through the northern
Rockies. Snow levels through Saturday are around 9000ft over the
Absarokas, Wind Rivers, and Bighorns, above which probs for >6"
snow from 12Z Saturday to 12Z Sunday are 40-80%.


The probability of significant icing is less than 10 percent.


Jackson


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FOUS11 KWBC 030808
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Fri Oct 3 2025

Valid 12Z Fri Oct 03 2025 - 12Z Mon Oct 06 2025

...Northern Rockies...
Days 2-3...

A pair of shortwaves moving across the Intermountain West will
interact with well above normal amounts of atmospheric moisture in
the area to cause the area's first winter storm of the season at
the higher elevations from Glacier NP in northern Montana south and
east through the ranges of northern and western Wyoming through
Sunday. The first shortwave begins the period Saturday morning over
Utah, and then tracks northeast towards the northern Plains by
Sunday morning. As the stronger of the two shortwaves getting first
dibs at the excess moisture across the area, expect heavier and
longer duration snow across the ranges of far southern Montana and
northwestern Wyoming, including Yellowstone and Grand Teton NPs.
Snowfall amounts of 6-12 inches are expected at the highest
elevations where the snow is most persistent.

As that first shortwave tracks into the Plains Sunday morning, the
second shortwave rounding the back of the longwave trough will dive southeastward out of Alberta through much of Montana from Saturday
night through much of the day on Sunday. This shortwave will result
in a period of heavy snow across much of Glacier NP late Saturday
night through Sunday morning. This secondary forcing will keep the
snow that began with the first shortwave Saturday ongoing through
Sunday. The snow will end from north to south Sunday and Sunday
night. WPC probabilities for more than 6 inches of snow remain over
50% for the Beartooth and Absaroka Ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 040724
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
324 AM EDT Sat Oct 4 2025

Valid 12Z Sat Oct 04 2025 - 12Z Tue Oct 07 2025

...Northern Rockies...
Days 1-2...

The weather pattern across the northern Rockies remains very
similar to previous runs of the guidance. The dynamic upper level
pattern will feature a deep upper level low over Utah ejecting
northeastward into the northern Plains by early Sunday morning.
Anomalous moisture to 2.5 sigma above normal will support waves of
showers and a few thunderstorms tracking northeastward as a
developing leeside low becomes the dominant surface feature through
the weekend. The leeside low will take advantage of a shortwave
trough also pushing northeastward. This will allow the surface low
to intensify as it makes its way to the Plains. Combined with
upslope enhancement, these ingredients all coming together will
lead to a prolonged period of heavy snow. The Beartooth, Absaroka,
and Big Horn Ranges will all come in with over 50% probabilites
for 6 inches or more of snow or more through Sunday. Behind this
first, stronger shortwave, a second shortwave will dive south out
of Alberta and into the Northern Rockies on Sunday. The presence of
this second shortwave will support maintaining heavy snow into
northern MT, especially Glacier NP. This digging second shortwave
will allow the larger longwave trough to remain in place, even
expanding and growing south and west. Similarly important to the
presence of these 2 shortwaves moving through the flow and taking
advantage of the abundant low level moisture, a large polar surface
high will effectively end the wintry threat from north to south.
This is because the polar high will also be quite dry, so it will
move the moisture feeding the snow on towards the north and east.
With that polar low in place, expect temperatures to tumble well
down into the 30s. Thus, as is very common in the wintertime, the
limited time between the advancing cold/dry air and the retreating
atmospheric moisture will favor certain areas, such as the
Beartooth Range, while keeping many others on the Plains bone dry.
With the advancing cold air, snow levels will fall to as low as
5,000 ft, but the dryness should hold any heavy snow occurring to
Sunday morning, before the snow ends from north to south.

WPC probabilities for 6 inches or more of snow remain between 50
and 90% for the Beartooth and Absarokas, while probabilities are a
bit lower, between 60 and 80% for the Wind River and Bighorn
ranges.

The probability of significant icing is less than 10 percent.

Wegman



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FOUS11 KWBC 050704
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
304 AM EDT Sun Oct 5 2025

Valid 12Z Sun Oct 05 2025 - 12Z Wed Oct 08 2025

...Northern Rockies...
Day 1...

A positively-tilted upper level trough stretching from the northern
Plains to Central California is directing much smaller shortwave
troughs around its periphery. As each shortwave moves across the
area, they've been producing an area of rain and higher elevation
snow as a surface low develops in response to the movement of the
individual shortwaves. The first shortwave is moving over the
Dakotas and taking a well-developed surface low along with it. The
surface lows have been taking advantage of an anomalous plume of
moisture from the northern Rockies to the northern Plains. This
abundance of moisture has helped support areas of snow at the
highest elevations. As the low pulls away, there may be a brief
break in the steadiest precipitation into the mountains. Meanwhile,
a second trough, not as strong but still potent, is diving south
across Idaho and will slow and turn eastward across southern
Wyoming by Monday morning. Behind this shortwave a strong polar
high will dive southward, bringing with it a much colder and drier
air mass. The combination of subsidence with the high, and the dry
air will very quickly end the snow from north to south. Into the
Beartooths and Absarokas, enough moisture may hang on to keep much
lighter snow ongoing into Tuesday morning in a few isolated areas.
By Tuesday morning, the entire longwave trough will have moved
eastward, allowing strong ridging to build into the West Coast.
This feature too will act to limit the heaviest precipitation in
all areas as subsidence works to end the snow.

With the overall forecast largely unchanged, we will see the back
edge of the precipitation move southeastward out of Canada and into
Montana by Monday afternoon. While localized upslope is a
possibility, the drier air with the advancing area of surface high
pressure will quickly win out, allowing some areas to get some
sunshine this afternoon.

WPC probabilities for over 8 inches of snow are between 60 and 80
percent for the Bighorns and Wind River Ranges through Monday
morning.

The probability of significant icing is less than 10 percent.


Wegman



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FOUS11 KWBC 090719
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
319 AM EDT Thu Oct 9 2025

Valid 12Z Thu Oct 09 2025 - 12Z Sun Oct 12 2025

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

By the end of the short range forecast period (Sunday morning) a
sharp, negatively-tilted upper trough is forecast to impact the
northern Rockies with moderate to heavy precipitation and lowering
snow levels. The upper trough configuration is expected to develop
as a closed-low currently off the coast of the Pacific Northwest
opens up and interacts with a diving shortwave out of British
Columbia. Additionally, this pattern is favorable for increasing
upper jet dynamics and is supported by model guidance depicting a
120-140kt southwesterly jet streak extending from the central
Great Basin to the central/northern Rockies. This places the
northern Rockies in the left-exit region of the upper jet and most
favorable for upper divergence and widespread moderate
precipitation. As the upper trough moves over the region Sat night
(500 mb heights estimated to be just below the 10th climatological
percentile per the 12z NAEFS) snow levels are expected to also fall
below 6,500ft across much of the northern Rockies by early Sunday
and below 5,000ft across the Pacific Northwest, where lighter
precipitation will be located.

The most impactful snowfall through this timeframe is expected to
be located across southwest Montana as moderate precipitation
overlaps with the lowering snow levels. Latest WPC probabilities
for at least 6 inches of snowfall are 20-40% across the high
terrain of southwest Montana above 8,000ft, which is still above
many of the major mountain passes. Additionally, WSSI-P values for
moderate impacts reach 30-40% in these areas primarily due to snow
load concerns.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell



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FOUS11 KWBC 100748
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
348 AM EDT Fri Oct 10 2025

Valid 12Z Fri Oct 10 2025 - 12Z Mon Oct 13 2025

...Northern Rockies & WA Cascades...
Days 2-3...

A strong upper-level trough traversing the Pacific Northwest on
Saturday will provide ample upper-level ascent over the Northern
Rockies Saturday night and into Sunday. The EPS shows a classic
"kissing jets" setup Saturday night with the diffluent left-exit
region of a strong 120-140 kt 250mb jet over Utah and the diffluent right-entrance region of a >100kt 250mb jet over south-central
Canada both located over western Montana. 18z ECMWF depicts PWAT
percentiles are likely to remain above the 90th climatological
percentile through early Sunday morning with ample moisture aloft
to saturate the DGZ over the Absaroka, Lewis Range, and Tetons.
There remains some uncertainty with varying solutions on the
depth/phasing of two 500mb disturbances over the Northwest. The GFS
is the most amplified of the bunch and is more amplified compared
to the GEFS mean, while the ECMWF/UKMET/EC-AIFS are in the middle
ground compared to the more overly amplified GFS and weaker/sheared
CMC solution.

With a lack of sub-freezing air ahead of the trough, even with a
encroaching colder, western Canadian high pressure system on
Sunday, this setup tends to favor the higher elevations of the
Northern Rockies. While a more amplified solution like the GFS
cannot be ruled out yet, the antecedent air-mass both ahead of the
storm and trailing behind the system are not overly impressive for
mid-October. As high pressure builds in from the north, colder
temperatures and easterly upslope flow will keep snow lingering
along the Lewis Range into Sunday night. Snowfall rates could
approach 1"/hr in the Lewis Range and around Glacier Nat'l Park
Sunday morning, which could also foster hazardous travel conditions
in nearby passes.

Additionally, a separate upper low is forecast to drop south into
the Pacific Northwest on Sunday within the same longwave western
U.S. trough. This will allow for snow levels to remain rather low
for this time of year (around and slightly below 4,000 ft) across
the WA Cascades along with favorable upper ascent, which may lead
to some light accumulating snow for the major mountain passes.

WPC probabilities through early Monday depict moderate chances
(40-70%) for snowfall >8" in the peaks of the Lewis Range above
6,000ft (including Glacier Nat'l Park) on south along the
Absaroka/Tetons above 8,000ft through Sunday afternoon. Lighter
snowfall accumulations as low as 5,000ft in the Lewis
Range/northwest Montana and 7,000ft in the Absaroka/Tetons are
expected. WPC's Probabilistic Winter Storm Severity Index (WSSI-P)
show similar chances for Minor Impacts for the event in these
mountain ranges. Other mountain ranges are likely to receive light
snow totals (2-4") as far west as the Bitterroots and as far south
as the Teton and Wind River Ranges in western Wyoming.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell/Mullinax




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FOUS11 KWBC 110736
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
336 AM EDT Sat Oct 11 2025

Valid 12Z Sat Oct 11 2025 - 12Z Tue Oct 14 2025

...Northern Rockies & WA Cascades...
Days 1-2...

Forecast remains on track for heavy snow to impact the high terrain
of the northern Rockies and WA Cascades beginning late tonight/early
Sunday morning and lasting through early next week, with certain
valley locations also potentially seeing the first snowflakes of
the season. Upper dynamics responsible for this October mountain
snow include a sharp upper trough crossing the northern Great Basin
today before taking on a negative tilt over the northern High
Plains on Sunday in tandem with a favorable duel jet structure.
This places the northern Rockies in an area of enhanced upper
divergence and lift, as well as crashing snow levels to allow for
precipitation to transition from rain to snow for areas above
5,000-6,000 ft. Snow levels are forecast to drop even lower on
Sunday across northwestern MT, where cold Canadian air noses
southward due to high pressure building to the north. This will
also allow for enhanced easterly upslope flow into the Lewis Range
and Glacier Natl Park region. Snowfall rates could peak at 1-2"/hr
in this part of northwest MT Sunday morning according to WPC's
Snowband Probability Tracker and make for difficult driving
conditions, especially at some of the major mountain passes in the
region.

Meanwhile, a separate deepening upper low will rotate southward
within the broad western U.S. trough by Sunday night over western
WA and provide additional lift along with a sinking cold front into
northern WA. Here, snow levels are expected to drop below 3,500ft
across the northern Cascades and contain light to moderate
snowfall at times into early Monday. WPC probabilities for greater
than 8" through Monday morning are high (70-905) across the Lewis,
Swan, and Mission ranges of northwest MT, as well as the northern
Cascades above 6,000ft. Probabilities for at least 8" of snow are
moderate (40-70%) across southwest MT and the northern Absarokas.


...Sierra Nevada...
Day 3...

By the end of day 3 (12Z Tuesday), the aforementioned upper low is
expected to rapidly drop south along the northern/central CA coast
and orient a corridor of 500-600 kg/m/s IVT (above the 99th
climatological percentile per the 12z NAEFS) orthogonal to the
central Sierra Nevada. There does remain some uncertainty regarding
exact track of the upper low and timing of heavy precipitation,
with the GFS and UKMET remaining on the slower end. Regardless, as
the plume of moisture approaches the central Sierra on Tuesday snow
levels are expected to remain around 6,000-7,000ft and snow ratios
should remain capped at around 8-10:1 given the moist fetch off
the Pacific. WPC probabilities for at least 8" of snow in the
central Sierra are currently moderate (30-60%) above 8,000ft through
the end of day 3, with more snow potential likely into the day 4
timeframe.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell


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FOUS11 KWBC 120744
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
344 AM EDT Sun Oct 12 2025

Valid 12Z Sun Oct 12 2025 - 12Z Wed Oct 15 2025

...Northern Rockies & Pacific Northwest...
Days 1-2...

By the start of the forecast period (12Z Sunday), a potent
shortwave upper-level trough will be quickly exiting the northern
Rockies along with an associated strong surface low pushing
northeastward into southern Saskatchewan. Gradually increasing
heights are then expected across the northern Rockies through the
remainder of the day 1 forecast period, while a rapidly deepening
upper low drops southward along the coast of the Pacific Northwest.
At the surface, cold Canadian high pressure nosing southward into
northwest MT will allow for favorable upslope ascent in this
region, with general low-to-mid level convergence extending across
northern WA and ID along a sinking frontal boundary. This will
favor light to moderate snow across areas above 5,000ft, but with
snow levels dropping enough for flakes to reach into parts of the
MT Front Range and adjacent High Plains at times on Sunday night.
For the Cascades of WA and OR, snowfall will be tied to the
dropping upper low as snow levels start around 4,000-5,000ft
(lowest in the northern WA Cascades) before eventually lowering to
around 3,000ft in WA and 4,500ft in OR on day 2.

WPC probabilities show moderate-to-high probabilities (50-80%) for
storm-total snowfall amounts >8" from the Cascades on eastward into
the northern Idaho Panhandle to the Lewis Range of Montana.
Mountains within and around Glacier Nat'l Park even have moderate
chances (40-60%) for over 12" of snow, particularly above 7,000ft.
The WSSI shows mostly Minor Impacts due to potentially slick travel
conditions, while some passes in Montana and Glacier Nat'l Park
may contend with Moderate Impacts that could result in road
closures.

...California...
Days 2-3...

...First heavy snowfall event of the season set to impact the
Sierra Nevada beginning Monday night...

By day 2, the upper low dropping southward along the West Coast is
forecast to deepen into a robust 500mb low off the northern
California coast. This sudden amplification of the 500mb trough
(18Z ECMWF shows 500mb heights below the 0.5 climatological
percentile and nearing October records off the California coast
Monday afternoon) is due to an impressive anti- cyclonic weak break
over British Columbia. The dramatic height falls and modest
500-700mb CAA aloft will support lowering snow levels down to
around 6000-6500ft through the Siskiyou and the Sierra Nevada
starting Monday and continuing into the first half of next week.
All guidance also shows a healthy IVT topping 400 kg/m/s helping to
direct plenty of Pacific moisture at the mountain ranges. Snow
arrives over the northern California mountains on Monday with the
heaviest snowfall occurring Monday night into Tuesday over the
Sierra Nevada. Guidance has come in snowier over the past 12-24
hours, and given the lack of deep, cold air aloft, snow is likely
to be a heavy/wet snowfall along the Sierra Nevada. This could
raise concerns for potential impacts to trees and infrastructure
given this is the first significant mountain snowfall in the Sierra
Nevada this season.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) by Wednesday morning, with maximum amounts up to 36"
possible. Latest WSSI-P shows high chances (70-99%) for Moderate
Impacts along the central Sierra Nevada with the Snow Amount, Snow
Load, and Snow Rate impacts being the main concerns for the first
significant snow of the season. Current WSSI also highlights Major
to Extreme Impacts, which would imply difficult to impossible
travel at times between Monday night and much of the day on Tuesday,
including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell/Mullinax





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FOUS11 KWBC 130745
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Mon Oct 13 2025

Valid 12Z Mon Oct 13 2025 - 12Z Thu Oct 16 2025

...California & Central Nevada...
Days 1-2...

...First significant snowfall event of the season set to impact
parts of the Sierra Nevada beginning Monday night...

An upper low dropping southward along the West Coast is forecast
to deepen into a robust 500mb closed low off the California coast
by Monday night before swinging inland across central California on
Tuesday and eventually the central Great Basin on Wednesday. This
rapid amplification of the 500mb closed low (18Z ECMWF shows 500mb
heights below the 0.5 climatological percentile and nearing October
records off the California coast Tuesday morning) is due to an
impressive anti- cyclonic wave break over British Columbia. Height
falls and modest 500-700mb CAA aloft will support lowering snow
levels down to around 6000-6500ft through the Siskiyou and the
Sierra Nevada starting today and continuing through early
Wednesday, with snow levels remaining around 7,000ft to start in
the southern Sierra within the more robust precipitation axis. A
healthy IVT topping 400 kg/m/s is helping to direct a rich plume of
Pacific moisture at the mountain ranges. However, recent model
trends over the last 24 hrs have indicated a slightly further south
location of the upper- low, which lowers the QPF somewhat across
the central Sierra due to less orthogonal (more southerly) flow
into the Sierra Nevada terrain. This produces better upslope flow
into the southern CA ranges (ptype primarily rain) and southern
Sierra Nevada versus the prior forecasts centered on the central
Sierra. Regardless, snow still arrives over the northern California
mountains today with the heaviest snowfall occurring late tonight
into Tuesday over the central/southern Sierra Nevada. Given the
lack of deep, cold air aloft, snow is likely to be a heavy/wet
snowfall along the Sierra. This raises concerns for potential
impacts to trees and infrastructure given this is the first
significant mountain snowfall in the Sierra Nevada this season.
WPC's Snowband Probability Tracker shows HREF guidance identifying
2-3"/hr rates over the southern/central Sierra Nevada Monday night
into Tuesday. Look for some heavy snowfall to spill into central
Nevada's taller ranges with anywhere from 12-24" of snowfall
possible over 8,000ft.

WPC probabilities show moderate-to-high chances (50-80%) for at
least 24" of snowfall throughout the central Sierra Nevada (above
8,000 feet) through Wednesday with maximum amounts up to 36"
possible. Latest WSSI-P shows moderate-to-high chances (50-80%) for
Major Impacts along the central Sierra Nevada with the Snow
Amount, Snow Load, and Snow Rate impacts being the main concerns
for the first significant snow of the season. Current WSSI also
highlights Major to Extreme Impacts, which would imply dangerous
to impossible travel at times between Monday night and much of the
day on Tuesday, including for many major passes.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Mullinax/Snell

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FOUS11 KWBC 140729
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
329 AM EDT Tue Oct 14 2025

Valid 12Z Tue Oct 14 2025 - 12Z Fri Oct 17 2025

...California & Central Great Basin...
Days 1-2...

...First significant snowfall event of the season continues across
the Sierra Nevada today...

A deep, vertically stacked mid-upper low churning off the coast of
central CA by the start of the forecast period (12Z Tues) is
forecast to swing inland today before crossing into the central
Great Basin on Wednesday. This mid-upper low pressure system is
very anomalous for the time of year, reaching below the 0.5th
climatological percentiles and nearing October records for the
first part of day 1 just of the CA coast. The depth of the system
will allow for ample upper ascent and orographic lift throughout
the Sierra Nevada, while decreasing snow levels from around 7000ft
this morning to as low as 5500ft this evening under the upper low.
Snow levels also drop to around 6000ft over the central NV ranges
by Wednesday. The strong inland moisture surge ahead of the low and
associated with an occluded/cold front will have IVT values around
500 kg/m/s at the start of the forecast period and allow for
moderate to heavy snow rates above the snow level. 00Z HREF mean
snow rates are 1-2"/hr over the central/southern Sierra Nevada from
12Z to 18Z today, with lingering bursts of 1"/hr snow possible
over the central Sierra underneath the upper low through Tuesday
night.

WPC probabilities show moderate-to-high chances (40-80%) for at
least 12" of additional snowfall after 12Z Tuesday above about
8000ft and greatest across the southern Sierra and White/Inyo Mts
just to the east. Probabilities through that time for >8" are also
40-80% around 7000ft (including Donner Pass on I-80). The WSSI
highlights Major Impacts for the High Sierra and remote central NV
ranges with moderate impacts for most cross Sierra road passes.


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

The low fills as it crosses the Great Basin, but remains closed as
it crosses over WY on Thursday. Lee-side cyclogenesis forms over
southeast WY Wednesday night with an increasing easterly component
to the low level flow to aid moisture transport over the western WY
ranges through Thursday morning with snow levels falling to around
7000ft after starting above 9000ft on Wednesday. Overall, snowfall rates
are not expected to be that great outside of an isolated convective
shower in the highest terrain with mainly longer duration light-to-moderate snow through the forecast period. WPC probs for >8" snow in 72hr
ending 12Z Friday are 60-90% for the Absarokas, Teton and Wind
River Range, as well as the Uinta Mts in Utah mainly above
10,000ft.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell


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FOUS11 KWBC 150721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Wed Oct 15 2025

Valid 12Z Wed Oct 15 2025 - 12Z Sat Oct 18 2025

...Central Great Basin & Northern Rockies...
Days 1-2...

A potent closed upper low, which impacted California and the Sierra
to start the week is forecast to cross the central Great Basin
today before lifting across the northern Rockies on Thursday. As it
does so, it is also forecast to gradually weaken, but still
provide ample broad scale upper ascent over the region. The
greatest potential for moderate to locally heavy snow will likely
be situated directly underneath the aforementioned upper low where
the greatest lift and steepest lapse rates exist. The 00z HREF
shows this potential for 1-2"/hr snowfall rates across the high
terrain throughout north-central and northeast NV between 18Z-00Z
today as snow levels drop as low as 7,000ft.

For the northern Rockies, strong south-southwesterly upslope flow
into the WY and UT mountain ranges will provide for more longevity
of moderate high elevation snowfall ahead of the mid-upper low on
Thursday. This includes the Tetons, Absarokas, Bighorns, Wind River
Range, as well as the Wasatch and Uintas of UT. Snow levels will
start out fairly high and around 9,000ft before dropping to around
7,000ft for areas underneath the mid-upper low as it pushes
northeastward. Snow should taper off by Thursday night as the
system quickly exits into the northern Plains and dry northwesterly
flow becomes the dominant regime again for the time being.

WPC probabilities for at least 8 inches of snow for this event are moderate-to-high (50-80%) across the Ruby Mts of northeast NV, as
well as many of the ranges surrounding Yellowstone NP, the WY
Bighorns, and the Uintas of UT. Most of these higher probabilities
reside over regions higher than 9,000ft in elevation.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Snell

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FOUS11 KWBC 160618
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
218 AM EDT Thu Oct 16 2025

Valid 12Z Thu Oct 16 2025 - 12Z Sun Oct 19 2025

...North-Central Rockies...
Day 1...

Upper low over southwestern Wyoming this morning will continue to
track northeastward into southeastern Montana by 00Z/17. Snow
levels will be around 7000-8000ft over the region. Light to modest
snow will continue over the Uintas and Absarokas/Wind River
Range/Bighorns this morning before ending late this afternoon into
the evening/overnight from southwest to northeast as the system
moves into the Northern Plains. WPC probabilities for at least
another 6 inches of snow after 12Z this morning are 20-50%.


...Northern Rockies...
Day 2...

Shortwave out of western Canada will slip southeastward across the
Northern Rockies Friday evening into Saturday morning, spreading
light snow across Glacier NP, southwestern
MT/Yellowstone/Absarokas, and into the Bighorns. WPC probabilities
for at least another 4 inches of snow are low (10%).

...Pacific Northwest...
Day 3...

Pacific upper low will push into southwestern Canada with a strong
130kt jet from southwest to northeast slowly sinking into the
region. Snow levels will be quite high through 00Z Sun
(6500-10,000ft across WA) but then start to crash through 12Z Sun
(end of the period) to around 5000-6000ft over the WA Cascades. WPC probabilities for at least 6 inches of snow are low (10-40%) over
the higher peaks of the Cascades through 12Z Sun.


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso

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FOUS11 KWBC 161845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
245 PM EDT Thu Oct 16 2025

Valid 00Z Fri Oct 17 2025 - 00Z Mon Oct 20 2025

...Northern/Central Rockies...
Days 1-3...

The mid-level pattern becomes increasingly progressive through the
weekend as the closed low which has brought prolonged unsettled
weather to the region fills. As this feature becomes embedded in
the more general westerlies by Friday night, it will leave pinched
W/NW flow in its wake, through which two additional disturbances
will race, producing transient periods of moderate to heavy
snowfall across the higher elevations.

On D1 /Thursday night and Friday/ some lingering mid-level moisture
will remain across the terrain of NW WY in response to a departing
surface low and increasing NW mid-level flow. While moisture is
expected to erode quickly during this period, sufficient upslope
flow into this moisture will result in periods of light to moderate
snowfall before the DGZ dries and snow ends, especially across the
Tetons and near Yellowstone NP, where WPC probabilities for an
additional 2+ inches of snow are as high as 30-50%.

After this first wave ejects to the east, a secondary shortwave
will dive southeast rapidly on its heels. This impulse is likely to
dig from southern British Columbia around 00Z/Friday to the
Central High Plains by 00Z/Saturday. A pinched vorticity streamer
accompanied by rapid sharpening of the 700mb wave will drive
intense ascent, albeit of short duration, from the Northern Rockies
through the terrain of WY. Although forcing will be quick,
favorable overlap of omega into the DGZ combined with modest 0-2km
fgen will likely result in a fluffier-than-normal snowfall with
SLRs likely above climo but with briefly intense rates above 1"/hr.
This will result in a few inches of snowfall as reflected by
WPC probabilities that reach as high as 50% for 4+ inches across
the Absarokas and Big Horns. Gusty winds will likely accompany
this wave and some low-end probabilities (10-20%) for moderate
blowing snow impacts from the WSSI-P move across the area during
this time as well, indicating a threat for convective snow bursts
or even an isolated snow squall Friday night.

Thereafter, yet another wave, the third in the series, will
approach the Pacific Northwest Coast and then dive into the
Northern Rockies by the end of the period. This system will be more
impressive with impressive height falls digging out of British
Columbia leading to robust downstream IVT surging into the region

80% chance for 250 kg/m/s reaching well into the interior West).

With the accompanying WAA, snow levels will rise steadily to
7000-8000 ft, but then crash with the accompanying cold front to
around 5000 ft by 00Z Monday. This will result in varying snow
levels with generally below climo SLR producing impacts due to snow
load as reflected by the WSSI-P, but additional snowfall before the
end of D3 is expected to be light and confined to the Northern
Rockies near Glacier NP.


...Pacific Northwest...
Day 3...

A strong upper low (500mb heights dropping below the 10th
climatological percentile according to NAEFS) will dig along the
British Columbia coast driving height falls into the Pacific
Northwest on Sunday. These height falls will be accompanied by
vorticity streamers/PVA, and increasing LFQ diffluence as a jet
streak pivots southward upstream of the primary trough axis.
Together, this will result in increasing ascent into a moistening
column thanks to IVT reaching above 500 kg/m/s (>80% chance) into
coastal WA and OR. The result of this overlap will be an expanding
area of precipitation, with snow likely becoming more widespread as
snow levels fall through the day. Initially, snow should be
confined to just the highest terrain of the Northern Cascades, but
by the end of D3 snow levels fall to around 5000 ft (NBM 10th/25th
percentiles seem reasonable due to strong ascent and steepening
lapse rates) leading to more widespread snow and at least some
impacts at the passes. WPC probabilities on Sunday at high (>70%)
for more than 4 inches in the Northern Cascades above 6000 ft and
in the higher peaks including Mt. Rainier.


The probability of significant freezing rain across CONUS is less
than 10 percent.


Weiss


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FOUS11 KWBC 170659
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Fri Oct 17 2025

Valid 12Z Fri Oct 17 2025 - 12Z Mon Oct 20 2025

...Northern Rockies...
Day 1...

A 125kt jet along 50N into southwestern BC will dip down across
the US/Canadian border as mid-level height falls push into western
MT late this afternoon and overnight. A surface cold front will
move quickly through the region with NW flow in its wake,
supporting a broader area of light snow and some enhanced upslope-
driven snow for the MT Absarokas and into the Bighorns. WPC
probabilities of at least 4 inches of snow are about 20-60% above
8000-9000ft.

...Pacific Northwest and Northern Rockies...
Days 2-3...

A buckled upper jet will move into the Pacific Northwest early
Sunday, with a cold front and attendant atmospheric river of
moisture aimed into the region from the southwest. High snow levels
above 7000ft early Sunday (coincident with the heavier
precipitation) will lower to just under 5000ft Sunday
afternoon/evening as heights reach their lowest point in the fast
flow. Snow will quickly spread from the WA Cascades eastward to the
northern Rockies (western MT/Idaho into northwestern WY) as the
cold front races eastward. WPC probabilities for at least 8 inches
of snow days 2-3 are >50% above about 5000ft over the WA Cascades
and around 6500ft in northwestern MT.

The probability of significant freezing rain across CONUS is less
than 10 percent.


Fracasso


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FOUS11 KWBC 190627
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
227 AM EDT Sun Oct 19 2025

Valid 12Z Sun Oct 19 2025 - 12Z Wed Oct 22 2025

...Pacific Northwest and Northern Rockies...
Day 1...

A cold front is moving quickly through Washington this morning
with its moisture plume aimed at the Cascades. This front will
continue to move eastward at a quick pace due to the progressive
yet still amplified upper pattern. Well above normal moisture
levels (PW anomalies >90th percentile) in the warm sector will
favor high snow levels ahead of the front (>7000ft) coincident with
the heavier QPF. This will limit snow accumulation to the highest
mountain peaks before snow levels drop sharply behind the front to
4500-5000ft. To the east, snow will spread across the northern
Rockies (northern Idaho/northwest Montana and into western WY) this
morning in advance of the cold front. High snow levels initially

8000ft will fall to around 5000-6000ft this afternoon. The quick

movement of the system will limit duration of the snow, and nearly
all the snow will clear the area by late Monday morning.

WPC probabilities for >8" of snowfall are >50% in the northern WA
Cascades above about 5000ft and will include Washington Pass
(SR-20) at nearly 5500ft elevation. To the east, WPC probabilities
for >8" of snowfall are >50% in the Bitterroots and Lewis Range
above 5000-6,000ft. Probabilities are lower over western Wyoming --
generally <40%.


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso

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FOUS11 KWBC 200551
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
151 AM EDT Mon Oct 20 2025

Valid 12Z Mon Oct 20 2025 - 12Z Thu Oct 23 2025

...Northern Rockies...
Day 1...

At the start of the period this morning, the upper trough axis
will be exiting the Rockies with heights building in quickly this
afternoon to Montana/Wyoming. Lingering mainly upslope-driven snow
this morning will end by the afternoon over parts of western
Montana into the Big/Little Belts, Absarokas, and Bighorns. WPC
probabilities for at least an additional 4 inches of snow are
20-60% here and some high mountains peaks could see another 6
inches of snow.

Elsewhere, light snow is expected over the CO Rockies this morning
near the cold front before ending this afternoon. No appreciable
snow is expected until Wednesday over the Sierra as an upper low
moves ashore but snow levels there will be very high (>9000ft).


The probability of significant freezing rain across CONUS is less
than 10 percent.

Fracasso



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FOUS11 KWBC 210629
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
229 AM EDT Tue Oct 21 2025

Valid 12Z Tue Oct 21 2025 - 12Z Fri Oct 24 2025

...CO Rockies...
Day 3...

An upper low in the Pacific (southwest of California) will move
into the Golden State on Wednesday, bringing some light snow to the
high Sierra (above 9500ft). On Thursday, it will cross through the
Four Corners region with antecedent LFQ jet ascent over
southwestern to central Colorado. Moisture levels will rise just a
bit to around +1 sigma (PW values 0.4-0.5 inches) though snow
levels will be high -- >10,000ft to start then decreasing overnight
Thursday into Friday morning to around 9500ft. At the end of this
forecast period, the upper low will likely be centered over south
central CO with snow continuing but starting to wind down. WPC
probabilities for at least 6 inches of snow are at least 40% above
11,000ft. This will likely impact high passes such as
I-70/Eisenhower Tunnel.

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

Fracasso

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FOUS11 KWBC 220624
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
224 AM EDT Wed Oct 22 2025

Valid 12Z Wed Oct 22 2025 - 12Z Sat Oct 25 2025

...High Sierra Nevada...
Day 1...

An upper low just southwest of Southern California this morning
will move inland and cross the southern Sierra Nevada this evening,
brining some light snow to the high mountains. Snow levels around
10,000ft will only fall to around 9500ft as the upper low passes
through. WPC probabilities for at least 6 inches of snow are low
(10-30%) above 10,000-10,500ft.


...Colorado Rockies...
Day 2...

On Thursday, the CA upper low will track into the Four Corners
region with some broad jet-divergence atop a moistening mid/lower-
layer. PWs will climb to near 0.50 inches with upslope-driven snow
into the San Juans northward to the central CO ranges. Snow levels
will be high -- 11,000ft to start on Thursday then falling to
around 9500ft Friday morning as the upper low moves. Still, this
will affect the high mountain passes such as I-70/Eisenhower
Tunnel. WPC probabilities for at least 6 inches of snow are >50%
above about 11,000ft. The highest peaks in the Sawatch Range

12,000ft) may see more than 8-10 inches of snow (30-60% chance).

...Northern Cascades...
Day 3...

Deep Northeastern Pacific trough on Friday will strong cold front
into WA and OR. Higher snow levels ahead of the front (6000-7000ft)
will sharply drop overnight into early Saturday to around
5000-6000ft (north to south along the WA to OR Cascades). WPC
probabilities for at least 6 inches of snow through 12Z Sat are

50% above about 6000ft in the WA Cascades with more snow to follow

into the weekend.


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

Fracasso


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