FOUS11 KWBC 210630
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
230 AM EDT Tue Apr 21 2026

Valid 12Z Tue Apr 21 2026 - 12Z Fri Apr 24 2026

...California... Days 1-2...

The heavily discussed and anticipated mid-level closed low
positioned off the CA/OR coast tonight will gradually lift E/NE,
with the core of the low progged to come onshore northern CA late
tonight/very early Wednesday morning. This evolution will result in
impressive height falls downstream into CA, with additional ascent
supplied by secondary shortwave energy rotating through this
trough and lifting northeast through the Great Basin. Impressive
height falls and PVA, working together with the LFQ of an upper
Pacific jet streak working onshore, will drive large scale ascent,
with lift becoming robust today and tonight.

This dep layer lift will act upon an increasingly moist column to
support widespread moderate to heavy precipitation. This moisture
will be channeled onshore via confluent flow E/SE of the upper low
and directly beneath the Pacific jet streak to drive IVT to around
500 kg/m/s as supported by the West-WRF and elevated probabilities
from the ECENS and GEFS (up to 60% chance). This steady stream
onshore of moisture will be wrung out by the aforementioned
synoptic lift, with additional ascent through upslope flow into the
terrain of northern CA and the Sierra providing locally enhanced
lift. ALthough snow levels will begin elevated at 6000-7000 ft,
they will crash rapidly beneath the upper trough, becoming as low
as 4500 ft, or even potentially lower (NBM 10th percentile is 3500
ft in the Sierra) due to steep lapse rates allowing for some precip-loading/dynamic cooling. This will result in heavy snow
accumulations in the terrain, especially above 6000 ft, but with
significant snowfall above 4500 ft also possible.

The heaviest snow is expected across the Sierra where D1 WPC
probabilities are high (>70%) for at least 12 inches of snow, and
1-2 feet is possible in the higher terrain. This will be in
response to snowfall rates that could reach 1-2+"/hr as reflected
by the WPC prototype snowband tool as the upslope flow into the
steep lapse rates aloft drives potential convective rates. With
this snow falling below many of the Sierra passes, treacherous to
impossible travel is likely (WSSI-P indicates a 40-50% chance of
major impacts due to heavy snow and wind). Farther north across the Shasta/Siskiyou/Trinity region, snow levels should generally remain
above the important travel passes, but in the higher elevations WPC probabilities are high (>70%) for at least 8 inches of
accumulation D1.

As the system ejects into the Great Basin and Northern Rockies D2,
the accompanying ascent will shift away from CA, bringing an end to
the heavy snow early Wednesday leaving only light/additional
accumulations across these areas.

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

The same system that will bring heavy snow to California will
continue its trek into the northern Rockies Wednesday into Thursday
as several pieces of shortwave energy pinwheel around and within a negatively-titled upper trough. Although moisture will gradually
decay (IVT less than 150 kg/m/s spilling into the Intermountain
West), a strengthening surface low across the northern High Plains
will work together with continued mid-level southwest flow
(funneling the Pacific moisture) to produce widespread
precipitation across the region beginning Wednesday morning.

Initially, snow levels are expected to be around 8000 ft, keeping
any significant accumulations confined to the highest elevations.
However, as the upper trough swings northeast, snow levels are
expected to fall steadily, becoming 4000-5000 ft by Thursday
morning, and falling even further to around 3000-4000 ft (possibly
as low as 2000 ft in the Northern High Plains) by the end of the
forecast period. While this still suggest that the heaviest
accumulations will occur in the higher elevations from the Blue
Mountains of OR through the Sawtooth/Salmon River area of ID and
into the Northern Rockies from near Glacier NP through Yellowstone
NP, some lower elevation accumulations are also becoming likely.

Confidence is high that heavy snow will accumulate in the terrain,
and this is reflected by 48-hr WPC probabilities (between 12Z Wed -
12Z Fri) that are high (>70%) for 8 inches in much of the higher
terrain between Glacier NP, Yellowstone NP, and west to the Blue
Mountains. Locally 18 inches of snow is possible (30% chance).

However, the most challenging aspect of this forecast involves what
happens on D3 as the surface low deepens across eastern MT and into
Canada. There continues to be diverging solutions of the various
global deterministic models with both the intensity of this low and
the accompanying upper level trough evolution. The GFS/GEFS
continue to look like the outlier/amplified scenario which is also
reflected in the D3/D4 clusters, but there has been a notable shift
to increase dispersion of the GEFS with more overlap from the
ECENS/CMCE from prior runs. However, 74% of the GEFS members still
make up the most amplified solutions, with nearly 1/2 of the GEFS
indicating the deepest trough and resulting heaviest snowfall into
the High Plains. While there is increasing confidence that
sufficient moisture lifting out of the Gulf will wrap into a TROWAL
and pivot SW around the low back into MT, the weaker solutions
supported by the ECENS/CMCE are still favored, especially noting
that the recent NAM has also trended away from the GEFS. Still,
there is potential for lower elevation snow from central to eastern
MT and eventually into ND, but at this time confidence is low in
any significant accumulations. It will need to be watched in
future model cycles however, for any potentially hazardous winter
weather outside of the terrain Wednesday into Thursday.

The probability for significant freezing rain exceeding 0.1 inches
across the CONUS is less than 10 percent.

Weiss
$$

--- ScorpioBBS/QWK v0.31a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 250734
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
334 AM EDT Sat Apr 25 2026

Valid 12Z Sat Apr 25 2026 - 12Z Tue Apr 28 2026

...Western U.S Overview...

A 500mb shortwave trough rotating around the southern flank of a
500mb low off the CA coast today will track across central
California Saturday night and reach the central Rockies by late
Sunday. Healthy PVA over the Rockies and the left-exit region of a
250mb jet streak positioned overhead will foster excellent upper-
level divergence while a healthy slug of 700-300mb moisture arrives
from the subtropical Pacific. Temperatures aloft are not overly
cold, so snowfall will be confined to the higher elevations of the
Sierra Nevada on east across the Intermountain West. Meanwhile, a
secondary trough over the Pacific Northwest will generate the same
favorable divergence aloft on Sunday. This trough will become more
sheared Sunday night into Monday, but it will contribute to the
longwave trough entrenched over the West. These features will work
together to bring beneficial snowfall to the Rockies this weekend
and into Monday.

...Sierra Nevada... Days 1-2...

Snowfall begins in the central/southern Sierra Nevada ahead of
this shortwave trough Saturday afternoon. Snow levels initially
around 7,500ft drop to around 6,000ft tonight before precip tapers
off. Some minor snowfall may linger on Sunday, but at the more
remote elevations above 9,000ft. Saturday and Sunday snow probs for

4" are >50% in the higher elevations of the Sierra Nevada south

of Sonora Pass and the White Mtns.

...Great Basin, central/southern Rockies, & the Black Hills... Days 2-3...

Precipitation quickly expands east from central NV and into the CO
Rockies Saturday night lingering through Sunday. Snow levels
linger around 8000ft in NV/UT while 9,000ft snow levels in CO drop
to 8,000ft Sunday evening. The aforementioned secondary trough
axis delivers more light precip to UT/CO, while also expanding the precipitation shield farther north across western WY and the
southern MT Rockies on Sunday. The presence of the longwave trough
over the West will keep periods of lighto-to-moderate mountain snow
in the forecast through Monday. Days 2-3 snow probs for >4" are
high (>70%) for just about all of the mountain ranges referenced,
with the more remote reaches of the Uinta and CO Rockies having at
least 50% chances for over a foot of snowfall. Accumulating snow is
likely as far east as the Black Hills, where WPC probabilities
sport low-to-moderate chances (20-40%) for >4" of snowfall.

While some locally hazardous travel over nearby passes are
possible, snowfall throughout the Central Rockies will be more
beneficial than harmful, on account of the below average snowpack
throughout the region.

The probability for significant icing over one-tenth of an inch is
less than 10 percent.

Mullinax
$$

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 260557
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
157 AM EDT Sun Apr 26 2026

Valid 12Z Sun Apr 26 2026 - 12Z Wed Apr 29 2026

...Great Basin, Central/Southern Rockies, & the Black Hills... Days 1-3...

A broad longwave trough over the western U.S. will direct a pair
of 500mb shortwaves troughs across the Intermountain West today and
the first half of the work week. A 250mb jet streak will place its
divergent left-exit region over the Central Rockies, while ample
700-300mb layer moisture streams overhead, providing an ideal setup
for mountain snow that extends from the Great Basin on east to the
Black Hills. Snow levels over NV/UT dip from around 8000ft to
about 7500ft while 9000ft snow levels in CO drop to 8000ft Sunday
evening. The heaviest snowfall will occur on Sunday from the
Wasatch and Uinta on east to the CO Rockies and northward to the
Wind River and Big Horn Ranges. As the longwave trough continues to
see spokes of 500mb vorticity maxima move through, light-to-
moderate snowfall will linger over the central and northern Rockies
through Monday and even into Tuesday.

72-hour WPC probabilities show high chances (>70%) for >12" of
snowfall in the peaks of the eastern NV Great Basin, the
Uinta/Wasatch, and the CO Rockies above 9,000ft. Similar high
chance probabilities exist for >8" of snowfall in the Wind River,
Tetons, Absaroka, and Big Horns. These peaks sport lot-to-moderate
chances (20-40%) for localized snowfall totals topping 12" through
Tuesday. Only the highest mountain passes will get impactful snow, so
the impending snowfall will mainly be a beneficial event for these drought-stricken area.

The probability for significant icing over one-tenth of an inch is
less than 10 percent.

Mullinax
$$

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 290722
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
322 AM EDT Wed Apr 29 2026

Valid 12Z Wed Apr 29 2026 - 12Z Sat May 02 2026

...Central & Southern Rockies... Days 1-3...

A pair of upper-level disturbances; one over the Great Basin and
another approaching the Central Rockies from the north, will work
together to produce a much-needed period of moderate-to-heavy
mountain snow from the WY Rockies on south through the CO/northern
NM Rockies. As these disturbances work together to gradually cause
500mb height falls, a robust 130kt 250mb jet streak will tap into
subtropical moisture at the same time that high pressure building
in over the Northern Plains forces easterly upslope flow into the
Front Range and Sangre De Cristo. Periods of light high-elevation
mountain snow (generally above 9,000ft) will occur Wednesday night,
but as the strong upsloping easterly winds arrive on Thursday,
snowfall rates will intensify along the Front and Park Ranges. The
Palmer Divide above 7,000ft is also likely to see periods of snow
Thursday afternoon, potentially causing some slick travel
conditions as the sun sets Thursday evening. Snowfall rates between
1-2"/hr are likely along the Front Range and Sangre De Cristo
above 9,000 Thursday afternoon and into Thursday night. Snowfall
rates diminish gradually Friday as easterly upslope flow gradually
lessens, but still manages to keep periods of snow in the forecast
for much of the day. A burst of heavier snowfall is likely along
the San Juans above 10,000ft as the trailing 500mb shortwave trough
pivots through the Four Corners region on Friday. Snow finally
tapers off some time Friday night.

WPC probabilities paint a snowy picture over the Central and
Southern Rockies, which is overall a great thing to see given the
ongoing drought and lack of snowpack. The heavier snowfall totals

12") are most likely to occur above 8,000ft along the Front

Range, the above 9,000ft along the Park Range and the Sangre De
Cristo. Some localized totals >20" are possible in the more remote
peaks pf the CO Rockies, including Pike's Peak. Generally 6-12" of
snowfall are likely along the San Juans above 11,000ft. The WSSI
does show mostly Minor Impacts at elevations between
8,000-10,000ft, with localized Moderate to Major Impacts at the
more remote elevations above 10,000ft. Some Minor Impacts are
depicted along I-25 over the Palmer Divide and Raton Pass, so some
locally hazardous travel conditions are possible Thursday
afternoon and evening.

Farther north, some light-to-moderatwe snowfall is likely in the WY
mountain ranges such as the Wind River, Big Horn, and Absaroka.
Most totals will range between 4-8" above 9,000ft with localized
amounts approaching 10" possible. The bulk of the snowfall there
occurs today, although some light snowfall looks to persist into
the first half of Thursday.


The probability for significant icing over one-tenth of an inch is
less than 10 percent.


Mullinax


$$

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 300807
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Thu Apr 30 2026

Valid 12Z Thu Apr 30 2026 - 12Z Sun May 03 2026

...Southern Rockies... Days 1-2...

Surface high pressure over the central Great Plains provides some
return flow and moisture up the southern High Plains to a frontal
boundary over Colorado Rockies through today where mountain snow
persists. Upper low pressure currently off the northern Baja
crosses south of Arizona tonight aiding lift over southern NM with
additional lift for the southern Rockies in northern NM. Snow
levels remain 6000-7000ft in CO today with Day 1 snow probs for >6"
40-80% down central CO ranges from the Front Range through the
Sangre de Cristos. Snow levels in the San Juans and southern Sangre
de Cristos in northern NM drop from around 9000ft to 8000ft tonight
where Day 2 snow probs for >6" are 30-60%.

Snow levels remain 10,000ft or higher in southern NM with just rain
expected there on Friday. Precip shifts east of NM Friday afternoon
as the southern tier low opens into a progressive trough over Texas.

The probability for significant icing over one-tenth of an inch is
less than 10 percent across the CONUS.

Jackson
$$

--- Scorpio BBS
* Origin: (618:250/6)

FOUS11 KWBC 020807
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 AM EDT Sat May 2 2026

Valid 12Z Sat May 02 2026 - 12Z Tue May 05 2026

...Sierra Nevada... Days 2/3...

A large, but modest amplitude mid-level low will swing onshore
central California Sunday night and drift to southern CA through
Monday night. Upslope precip begins Sunday afternoon, but snow
levels will be around 9500ft before dropping to around 8000ft late
Sunday night. Snow levels will then be around 7500ft under the low
on Monday when the precip should be the most consistent. Day 3 snow
probs for >6" are generally 40-70% for the High Sierra.

...Wyoming and Colorado... Day 3...

Low pressure swings through western Ontario Sunday night with a
potent cold front sweeping down the Northern Plains in its wake.
A digging mid-level trough behind the front provides lift over an
existing frontal boundary ahead of the aforementioned low moving
over CA before the cold front shunts activity a bit farther south
on Tuesday. There is uncertainty in the placement of this frontal
zone with the GFS farther north in central WY and the EC remaining
farther south along the WY/CO border. The front should be fairly
stationary once it is set up, so there could be a decent duration
to precip with snow levels dropping to around 7000ft behind the
cold front. Day 3 snow probs for >6" are 30-60% in the Wind River
and Bighorn ranges as well as around 50% on the Laramie Mtns and
20-40% on the Front Range in northern CO. Decently heavy mountain
snow then persists through Tuesday, so more info is to come on this system.

The probability for significant icing over one-tenth of an inch is
less than 10 percent across the CONUS.

Jackson

$$

d

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)