FOUS11 KWBC 140755
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Tue Apr 14 2026

Valid 12Z Tue Apr 14 2026 - 12Z Fri Apr 17 2026

...CO Rockies... Day 1...

Upper low over southwestern UT this morning will move eastward and
weaken slightly into a strong trough as it enters the CO Rockies
this evening. SW flow will help bring in some moisture to the
region which will wring out light to moderate snow over the
Rockies. Snow levels will be around 7500-8000ft, so any significant accumulations of at least 6 inches are >50% above about 10,000ft.

...Pacific Northwest through the Northern Rockies... Days 1-3...

Active wintry pattern from the Pacific Northwest through the
Northern Rockies starts today. A strong upper low moving
southeastward along the BC coast will dive into western WA tomorrow
evening and past the Divide Thursday evening. The upper low will
split into two pieces -- the northern portion will continue
eastward as a weakly closed upper low while the southern portion
will sink farther south into the Great Basin. Though moisture will
be rather limited (just a narrow surge of moisture ahead of the
cold front), heights and mid/lower-level temperatures will be well
below average and below the 1st percentile for this time of year,
reminiscent of a mid-winter system.

Rain and mountain snow will precede the cold front today with
initial snow levels around 3500-5000ft along the Cascades and
5000-6000ft over the Northern Rockies. Snow will increase later
this afternoon and tonight via upslope enhancement with rates of
1-3"/hr possible in the higher elevations, generally above the
passes. Cold front should push through the WA Cascades early
Wednesday which will push the heavier snow rates southward to stay
just ahead of the front into the OR Cascades. Snow levels will fall
to around 1000-1500ft tomorrow morning behind the front as snow
lightens. However, the upper low will then swing through with its
cold core and additional snow to around 1500-2000ft during the
afternoon hours. To the east, snow will increase over the Northern
Rockies where the cold front will take nearly a day longer to reach
past the Divide. There, too, snow levels will fall sharply behind
the front down to below 2000ft (i.e, all valley floors) where at
least some accumulation is probable. On Thursday
afternoon/overnight, the upper low will move through the Northern
Rockies with additional light to moderate snow mainly over SW MT
southward. Through 12Z Friday, with the strongest height falls over
northern UT into WY, snow will be favored over the northern
Wasatch/Unitas but especially into Wyoming (Bighorns) as it ends
over the Pacific Northwest.

WPC probabilities for at least 6 inches of snow are >50% above
about 2000-3000ft in the Cascades, 4000ft in the Northern Rockies,
and 7000ft in Wyoming. For at least a foot of snow, WPC
probabilities are >50% above about 3000-4000ft in the Cascades
(this includes Snoqualmie Pass), 5000-6500ft in the Northern
Rockies, and 9000-10,000ft in Wyoming. Total accumulations may
range from 1-3ft in the region, along with windy conditions, making
for very difficult to impossible travel through the terrain.

Additionally, the combination of the sharp cold front and well
below normal mid-level temperatures could yield some snow squalls
or at least some convective snow along/ahead of the front Thursday,
despite it being April (outside the more typical period). This
could cause short-lived but impactful drops in visibility and
hazardous travel.

The probability of significant icing for days 1-3 across the CONUS
is less than 10 percent.

Fracasso

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 150653
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
253 AM EDT Wed Apr 15 2026

Valid 12Z Wed Apr 15 2026 - 12Z Sat Apr 18 2026

...Cascades... Day 1...

Strong upper low approaching Vancouver Island this morning will
continue southeastward today, with a lead cold front moving through
the WA Cascades. The heaviest snowfall will be just ahead of the
cold front this morning from the southern WA Cascades into the OR
Cascades. Snow levels will fall from 3500ft ahead of the front to
1000-1500ft behind the front as snow briefly lightens. The trailing
upper low will bring in more light to moderate snow for the region
this afternoon/evening and this will gradually end by tomorrow
morning. WPC probabilities for an additional 6 inches of snow are

50% above about 2000-2500ft.

...North to Central Rockies and central High Plains... Days 1-3...

The upper low will cross the Divide on Thursday and split into two
pieces -- the northern portion will continue eastward along the
Canadian border as a weakly closed low while the southern portion
digs through the Great Basin before turning east to the central
Rockies. This will spread snow over much of the region as colder
winter-like air ushers in behind the cold front. With the SW flow
aloft, the central ID ranges, SW MT, and WY ranges will be the
focus for the heaviest snow. By Friday, height falls reach the
western High Plains where a low-level upslope component to the CO
Rockies and adjacent High Plains will promote additional snowfall
in the wake of the cold front. All snow will end around 12Z
Saturday as the trough continues steadily through the Plains to the
Upper Midwest.

For the Northern Rockies, the cold front will reach northwest MT
Wednesday morning with a gradual progression to Wyoming through
Wednesday night. The cold air behind the front is impressive (700mb
temps -12 to -16C) which will plunge temperatures 25-35 degrees
pre- to post-FROPA. Snow levels ahead of the cold front will be
around 5000-6000ft over MT before dropping to 2000-3000ft behind
the front as rates decrease. Snow levels over WY rise to 8000ft in
the warm sector Wednesday before dropping to 3000ft Wednesday night
behind the front. Snow levels around 9000ft in CO on Thursday drop
to 4000-5000ft through the day Friday.

WPC probabilities for at least 8 inches of snow are >50% above
about 5000ft in northern ID/northwest MT and 6000ft in the central
ID ranges. Over southwest MT (Absarokas) to the Tetons, Wind River
Range, and Bighorns, WPC probabilities for at least 8 inches of
snow are >50% above about 7000-9000ft from northwest to southeast.
Over UT into CO, amounts will generally be lighter but at least 6
inches of snow is likely (>50% chance) above about 9000ft. Lighter
amounts (1-2") are expected along/east of the Front Range into
metro Denver as rain turns to snow Friday evening.

As a final note, the sharp cold front should produce snow squalls
or convective snow bands along/ahead of it today and Thursday. This
activity could cause short-lived but impactful drops in visibility
and hazardous travel.

The probability of significant icing for days 1-3 across the CONUS
is less than 10 percent.


Fracasso
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 160756
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EDT Thu Apr 16 2026

Valid 12Z Thu Apr 16 2026 - 12Z Sun Apr 19 2026

...North to Central Rockies and Central High Plains... Days 1-2...

Shortwave trough moving across the interior Northwest will amplify
as it traverses into the Rockies, with 500-700mb heights falling
to between the 1st and 10th percentiles of the CFSR climatology.
This feature will remain generally progressive despite the
amplification, leading to broad but impressive ascent through
height falls/PVA combined with jet-level diffluence (with some
coupling noted over the Central Rockies leading to lee
cyclogenesis/surface low development.

Moisture will increase modestly, primarily in the 500-700mb layer
as streamlines suggest Pacific flow downstream of the primary
trough axis leading to elevated specific humidity in the mid-levels
despite TPWs remaining near-normal. Where the broad synoptic ascent
overlaps the greatest mid-level moisture, precipitation will
overspread the region, generally falling as light to moderate snow
above 6000 ft, at least initially. However, these snow levels will
fall to as low as 2000-3000 ft behind a sharp cold front which will
traverse E/SE beneath the primary trough, with upslope flow into
terrain and steep lapse rates beneath this cold core leading to
enhanced ascent and locally even lower snow levels at times.

Since this system remains progressive, total snowfall will be
somewhat modest, but locally much heavier accumulations are likely,
especially in the WY/CO terrain where some easterly low-level flow
around the developing surface low will enhance moisture and ascent.
2-day WPC probabilities indicate the heaviest snowfall will occur
across the higher elevations from the Absarokas into the Wind
Rivers, Big Horns, Laramies, Park Range of CO, and Front Range. In
these areas, the probability of at least 8 inches of snow is
between 50-90%, with locally more than 12 inches possible (30-50%)
across the Big Horns. Lighter snows (up to 4") are likely into the
High Plains of WY and CO, including along the Palmer Divide.

Additionally, snow squalls continue to appear possible along the
cold front, especially across parts of NV, UT, and WY today. While
snow accumulations from any squalls will be minimal, briefly heavy
snow rates and gusty winds could create dangerous travel.

...Northern Plains... Days 1-2...

The strong cold front moving through the Central Rockies and High
Plains Thursday into Friday will continue eastward, reaching the
Northern Plains by Friday morning. Behind this front, the upper
trough will split, with a closed northern stream impulse moving
along the ND/Canada border on Friday, while secondary jet energy
lifts into the Upper Mississippi Valley to help drive ascent. The
overlap of the low-level baroclinic zone and this jet evolution
will result in impressive mid-level fgen acting upon a modestly
moistening column to produce a stripe of heavy precipitation.
Forecast profiles indicate that the low-level thermal structure
will be marginally favorable for snow, but the strong ascent into
(or just above) the DGZ will help dynamically cool the column to
result periods of heavy snowfall rates which could reach 1-2"/hr
at times as reflected by the WPC prototype snowband tool. With most
of this occurring before daybreak Friday, the snow could
accumulate efficiently during p-type changeover, and WPC
probabilities indicate a low risk (10-30% chance) of 4+ inches of
snow within this band, especially in parts of ND. Farther east,
some light mixed precipitation is also possible, reflected by WPC
probabilities that rise to 50-70% for at least 0.01" of ice for
parts of NW MN.

Weiss

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 170709
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 AM EDT Fri Apr 17 2026

Valid 12Z Fri Apr 17 2026 - 12Z Mon Apr 20 2026

...North and Central Rockies through the Northern Plains... Day 1...

De-ampifying shortwave trough will pivot E/NE across the Central
Rockies and Northern Plains through Saturday morning. Broad ascent
ahead of this trough (through a combination of height falls and
PVA) will interact with modest upper level diffluence within the
RRQ of a meridionally arcing, but weakening, jet streak. At the
surface, a cold front surging eastward will provide additional
ascent through convergence, with mid-level fgen in its wake
providing a focus for heavier precipitation as well.

Moisture will remain elevated through this evening thanks to a
combination of Pacific moisture streaming over the Rockies on broad
SW mid-level flow and southerly flow out of the Gulf lifting into the Plains.

This will result in two axes of precipitation: lingering fgen mixed rain/snow/freezing rain in the Northern Plains, and continued light
to moderate snow across the Central Rockies. The heaviest snow and
ice in the Northern Plains is expected before 12Z, but residual
light freezing rain/snow through this aftn could result in light
accumulations of snow (less than 2 additional inches) and freezing
rain (less than 0.05 inches) from NW MN through the Arrowhead.
Farther south into the Central Rockies, especially in the higher
elevations of CO including the Park Range and Front Range, WPC
probabilities for 4+ inches of snow remain elevated at 50-70%
through D1 before precip shuts off tonight.

...Upstate New York/Northern New England... Day 3...

A strong cold front will cross from Upstate NY Sunday morning to
well of the Atlantic Coast by Monday morning. A narrow corridor of
robust warm and moist advection ahead of this front will bring
periods of rain to New England, but as the the cold front races
east, temperatures will crash dramatically behind it. While this
front will also cause rapid drying of the column, there appears to
be enough of a residual SW flow in the mid-levels to allow for
anafrontal precipitation to continue, which will fall as snow in
the higher elevations of Upstate NY (in the Adirondacks) as well as
the Greens of VT, Whites of NH, and mountains of interior
western/northern ME. While snowfall accumulations should be
generally modest, a few inches of snowfall is possible as reflected
by WPC probabilities indicating a 10-30% chance of 4+ inches in
these higher elevation regions.

Weiss

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 180559
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
159 AM EDT Sat Apr 18 2026

Valid 12Z Sat Apr 18 2026 - 12Z Tue Apr 21 2026

...Upstate New York/Northern New England... Day 2...

A strong cold front driven by a potent vorticity streamer/shortwave
embedded within larger cyclonic flow centered over the Great Lakes
will race eastward across Upstate NY and New England early on
Sunday. The cold front likely outraces the accompanying mid-level
trough axis, which results in continued SW flow aloft, keeping
sufficient moisture present in the column as the low-level thermals
cool dramatically. This suggests that precipitation ahead of the
front, which will be rain, will rapidly transition to a period of
snow behind the front, especially in the higher elevations of the
Adirondacks, Greens, and Whites. The duration of snow after
changeover will be limited due to subsequent column drying, but NW
flow in the wake of this front will promote at least a period of
upslope enhancement to slow the drying enough for a few inches of
snow in these higher elevations. WPC probabilities have been
consistent the past few runs, and continue to suggest a 10-30%
chance for at least 4 inches of snow in the higher terrain from
northern Upstate NY through VT, NH, and western ME.

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

Weiss
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 190713
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
313 AM EDT Sun Apr 19 2026

Valid 12Z Sun Apr 19 2026 - 12Z Wed Apr 22 2026

...Upstate New York/Northern New England... Day 1...

Strong cold front pressing east beneath increasing mid-level
cyclonic flow will cross New England Sunday morning with rapid
temperatures drops in its wake on impressive CAA. Moisture
streaming northward ahead of the front will fall as rain, but as
temperatures cool dramatically, precipitation will change to snow,
especially in the higher terrain of the Adirondacks, Greens,
Whites, and highest elevations of western/northern Maine before a
slow end as the column dries tonight. WPC probabilities remain
around 30-50% for 4+ inches of snow across the higher elevations
of this region.

...California... Day 3...

Closed 500mb low will gradually translate east to come onshore
northern CA Tuesday aftn/eve. The guidance has been slowing with
this evolution over the past few model runs, but pronounced WAA
southeast of the core of this low will spread elevated IVT (>90%
chance of at least 250 kg/m/s and locally as high as 500 kg/m/s
according to the West-WRF) into CA late D2 into D3. This enhanced
IVT will moisten the column to result in widespread precipitation
as height falls and an accompanying Pacific jet streak move onshore
CA. Snow levels at precipitation onset will be 6000-7000 ft, but
should fall steadily beneath the upper low, becoming as low as 5000
ft by the end of the forecast period. However, steep lapse rates
beneath the upper low combined with strengthening ascent through
upslope flow, especially across the Sierra, may allow snow levels
to drop even further as reflected by NBM 10th% snow levels falling
below 4000 ft by 12Z Wednesday. While the heaviest accumulations
are expected to be above 5500 ft in the Sierra and Shasta/Trinity
region, some light accumulations are possible at these lower
elevations as well.

WPC probabilities for at least 8 inches of snow have climbed to
above 70% above 6000 ft in the Sierra and parts of the northern CA
terrain, and it is becoming likely that a warning-level snow event
will cause impact to travel across the Passes on Tuesday. After
coordination with the local WFOs, due to uncertainty in timing of
the event (as model trends have slowed) no hazards will be issued
yet, but it is likely in the next 1-2 model cycles winter storm
watches will be needed for the Sierra and possibly other
neighboring terrain as this event spreads northeast through mid-week.

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

Weiss

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 200651
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
251 AM EDT Mon Apr 20 2026

Valid 12Z Mon Apr 20 2026 - 12Z Thu Apr 23 2026

...California... Days 1-3...

Impressive upper low (500mb heights falling to the 2.5 percentile
level of the CFSR climatology) will approach the CA coast tonight
before swinging onshore Tuesday aftn. Although this feature is
likely to slowly decay with time D2 into D3, pronounced ascent
through height falls, PVA, and the LFQ of a jet streak pivoting
onshore downstream of the primary trough will help expand
precipitation across CA beginning this morning. The heaviest
precipitation is likely late Monday night through Tuesday evening
as the greatest IVT (50-60% chance of exceeding 500 kg/m/s from
both the ECENS and GEFS) pushes into CA within the confluent flow
southeast of the trough. While most of the precipitation will occur
as rain due to elevated snow levels, snow is likely in the highest
terrain of the Sierra and Shasta/Trinity region, especially Tuesday
as snow levels fall from around 6000-7000 ft down to as low as 4500
ft, potentially locally lower as steep lapse rates and
impressive ascent dynamically cool the column (the NBM 10th% snow
level drops to 3500 ft in the Sierra).

This will result in heavy snow accumulations, especially across the
Sierra, but also into the higher elevations of the northern CA
terrain as well. The most significant snowfall is likely today and
Tuesday before the strongest ascent lifts away to the northeast on
Wednesday, bringing an end to CA snow on D3. Before that occurs,
however, WPC probabilities indicate a high risk (>90%) for at least
12 inches of snow in the higher Sierra (above 6000 ft), with
lighter accumulations down to 4500 ft. Heavy snow is also likely in
the Shasta/Trinity region as reflected by WPC probabilities that
are above 70% for at least 8 inches. This will create hazardous
travel across the Sierra passes.

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

The same upper low which will bring heavy snow to California Monday
and Tuesday will continue its trek northeast on Wednesday as a
weakening, but still amplified, trough swinging into the Northern
Rockies. 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 SW flow (funneling the Pacific moisture) to
produce widespread precipitation across the region beginning
Wednesday morning. Sufficient synoptic ascent into this moistening
column will manifest as areas of heavy snow, initially only above
8000 ft, but then falling to around 5000 ft by the end of the
forecast period as the upper trough swings overhead. WPC
probabilities D3 suggest there is high risk (>70%) for widespread
light to moderate snowfall accumulations exceeding 4 inches from
the Blue Mountains of OR through the Sawtooth/Salmon River ranges
of ID, into the Absarokas, Little Belts, Tetons and other areas
around Yellowstone NP, and as far north as the Lewis Range around
Glacier NP. Locally, more than 8 inches is possible (30% chance)
near the Absarokas, Little Belts, and Tetons.

Although current model snowfall accumulations outside of the
higher terrain are modest, there is some concern that low-level
southerly flow downstream of the surface cyclone will pivot
cyclonically and lift the accompanying theta-e ridge into a TROWAL
across Montana D3. The new guidance is trending in this direction,
which could support some heavier snow banding across western parts
of the state. As of this time the probabilities for heavy snow
remain low, but this will need to be monitored for potentially
impactful snow dropping into lower elevations on Wednesday.

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

Weiss

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 220635
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
235 AM EDT Wed Apr 22 2026

Valid 12Z Wed Apr 22 2026 - 12Z Sat Apr 25 2026

...Intermountain West to the Northern High Plains... Days 1-3...

Large mid-level trough/gyre will lift northeast from the Great
Basin into the Northern Rockies while re-amplifying into a closed
low by Thursday morning. This large scale trough will bring
widespread synoptic ascent across the area, while secondary and
even tertiary shortwaves rotating around the larger system bring
additional ascent to locally maximize snowfall across the area.

While confidence is high in widespread snow, especially in the
higher terrain as snow levels begins around 7000-8000 ft before
falling steadily to 4000-5000 ft by Thursday, there is still
significant uncertainty into how the low elevations will fare. In
the higher terrain, especially D1 and D2 from the Blue Mountains of
Oregon through the Sawtooth/Salmon River ranges, east into the
Northern Rockies from near Glacier NP through Yellowstone NP
including the Lewis Range, Little/Big Belts, Absarokas, Tetons,
and Wind Rivers, WPC probabilities are high (>70%) for at least 8
inches of snow, with 1-2 feet possible (30-50%) in the highest
elevations of many of these ranges.

The challenge for this forecast then primarily involves around what
happens in the lower elevations, as well as how ascent responds to
overlapping secondary forcing as a cold front and shortwave dig
southward behind the primary surface low beneath the larger trough.
This may lead to two areas of heavier snowfall.

1) As the primary low deepens over far NE Montana, moisture
wrapping cyclonically around it (low-level flow emerging from the
Gulf) will lift into a TROWAL and pivot southwest back into MT. The
guidance has been insistent in this evolution, but still vary
widely in the intensity and position of this developing
deformation. Should this TROWAL become more intense, as reflected
by the GFS/NAM, but not as much in the ECMWF/CMC, a band of heavy
snowfall into the lower elevations is possible for central and
eastern MT. At this time that is not the likely scenario, but still
worth monitoring as the combination of dynamic cooling and heavy
snow rates could produce a few inches of snow in a short period of
time on Thursday.

2) The secondary shortwave digging out of Canada on the backside of
the larger trough will interact favorable with the low-level
baroclinicity (fgen) as the cold front sinks southward towards
northern WY. Impressive mesoscale ascent through the fgen/height
falls will overlap with intensifying upslope flow in the wake of
this front to create a swath of moderate to heavy snowfall from
Thursday night through Friday night in a relatively narrow
corridor from central ID through eastern WY. While some of this
heavy snow will occur atop areas that receive significant snowfall
from the first impulse, this secondary impulse could result in
snowfall reaching as low as 2500 ft according to the NBM. The exact
placement and intensity of this secondary corridor remains
uncertain as well, but where it does occur, WPC probabilities
indicate a moderate to high risk (50-90% chance) of at least 4
additional inches (or 4 new inches in lower elevations) with heavy
snow rates up to 1"/hr.

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

Weiss
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 230706
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
306 AM EDT Thu Apr 23 2026

Valid 12Z Thu Apr 23 2026 - 12Z Sun Apr 26 2026

...Northern Rockies to the High Plains... Days 1-2...

A 500mb vorticity maximum diving south from Alberta will interact
with a negatively-tilted disturbance over eastern MT to produce a
large and strengthening closed-low over south-central Canada
Thursday night. The 500mb pattern over North America by Friday
features a +PNA and -NAO regime that effectively weakens the 500mb
zonal flow over the continent and causes this closed low to remain quasi-stationary into the upcoming weekend. A steady stream of
700-300mb moisture on the western flank of the strengthening upper
low will be placed over the Northern Rockies while, at the same
time, surface high pressure over western Canada builds in. This
combination of easterly upslope flow via strengthening high
pressure to the north, along with a more than sufficient 850-700mb
CAA aloft will support periods of moderate-to-heavy snow over much
of the Northern Rockies, including ranges as far south as the
Tetons, Wind River, and Big Horns. The heaviest snow will reside
over the Bitterroots, Lewis Range, and Absaroka where upslope flow
and the core of the coldest temperatures aloft will reside the
longest with snow lasting through the day on Friday. Snow levels
will crash as low as 2,000ft in western MT and northern ID.

Perhaps the trickiest aspect of this forecast is the deformation
zone banding on the western and southwest flank of the develop
upper low this morning. Around 12Z, latest 00Z CAMs show the
atmospheric column cooling enough to support moderate-to-heavy snow
in northeast MT. After subsiding Thursday afternoon, 500mb
vorticity maxima revolving around the western flank of the closed
low looks to reinvigorate snow showers Thursday night and into
Friday morning. The NAM CIPS snow squall parameter shows a staunch
signal for snow squalls early Friday morning that could still
persist through the day given the unusually cold temperatures aloft
when combined with strong surface based heating during the day.
Snowfall totals are likely only to be around a coating to 2"in
these areas, but given north of the MT border, a narrow axis of >6"
snowfall totals is depicted in southern Saskatchewan. Any 50-100
mile shift south in the TROWAL axis over southern Canada could lead
to locally heavier amounts over northern MT that surpass 6".

WPC probabilities for this event show moderate-to-high chances
(50-80%) for snowfall totals >12" in the peaks of the Northern
Rockies above 6,000ft. Some hazardous travel impacts at pass level
are likely, although with NOHRSC showing many of these mountain
ranges with below normal snow depth for late April per NOHRSC, most
of the expected snowfall will be welcome. WPC probabilities also
snow a small portion of northeast MT with moderate-to-high chances
(50-80%) where snowfall totals >4" are depicted, suggesting some
members of the WPC super ensemble do in fact show the heavy snow
banding potentially protruding into northeast MT. The WSSI
generally shows Minor to locally Moderate Impacts in all of these aforementioned locations with Snow Amounts being the primary driver
in impact over the Northern Rockies. The WSSI suggest Blowing Snow
is the bigger potential impact from the Little Belt and Big Snowy
Mountains on east into the High Plains of northern MT.

...Sierra Nevada & Central Rockies... Day 3...

A 500mb shortwave trough rotating around the southern flank of a
500mb low off the CA coast will track into the Southwest U.S. on
Saturday, bringing with it a slug of 700-300mb moisture.
Temperatures aloft are not overly cold, but healthy 500mb
vorticity advection coupled with the diffluent left-exit region of
a 250mb jet streak aloft supports vertical ascent. Plus, a 250-500
kg/m/s IVT over the Southwest supplies the Pacific moisture needed
to foster mountain snow. The lack of a very cold air-mass and the
progressive nature of this shortwave trough will keep snowfall
amounts more beneficial than harmful at a time where these mountain
ranges could use more snowpack. WPC probabilities show moderate-
to-high chances (50-70%) for snowfall totals >4" in southern
Sierra Nevada above 8,000ft and the more remote reaches of the
Wasatch, San Juans, Uinta, and central CO Rockies.

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

Mullinax

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 240721
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
321 AM EDT Fri Apr 24 2026

Valid 12Z Fri Apr 24 2026 - 12Z Mon Apr 27 2026

...Northern Rockies & Northern High Plains... Day 1...

Cyclonic flow around the large closed upper-low will continue to
keep snow showers (and some snow squalls) in the forecast across
northern MT and far northwest ND today. Residual 700-300mb layer
moisture combined with easterly upslope flow will also support
additional mountain snow from the Bitterroots and Lewis Range on
south into the Absaroka, Tetons, Wind River, and Big Horn ranges.
Snow will gradually taper off this evening and remain light across
the Northern Rockies through early Saturday morning. WPC
probabilities show moderate-to-high chances (50-70%) for additional
snowfall totals >4" in the mountain rages of central MT, the Big
Horns, and the peaks of the WY Tetons. Additional light
accumulations of a coating-2" are likely along the MT/Canada
border. There are also low-to-moderate chanceS (20-40%) for
snowfall amounts >4" in the peaks of the Black Hills through Friday night.

...Sierra Nevada to the Southern & Central Rockies... Days 2-3...

A 500mb shortwave trough rotating around the southern flank of a
500mb low off the CA coast will track into the Southwest U.S. on
Saturday. 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. Snow levels
around 7000ft on the Sierra Nevada at onset Saturday afternoon drop
to around 6000ft Saturday night before tapering off.

48-hour WPC probabilities show moderate-to-high chances (50-80%)
for snowfall totals >8" in the Uinta and San Juans, with similar
odds for >4" of snow in the southern Sierra Nevada. Some of the
more remote peaks of the Sierra Nevada could see close to 10" of
snow, while the remote reaches of the Uinta and San Juans receive a
much-needed 12" of snowfall. Farther north, the Wind River, Tetons,
WY Absaroka, and Big Horns are likely to receive at least another
4" of snowfall on top of the snow they measured from the Thurs-Fri
storm system.

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

Mullinax
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 270720
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 AM EDT Mon Apr 27 2026

Valid 12Z Mon Apr 27 2026 - 12Z Thu Apr 30 2026

...Great Basin, Central/Southern Rockies, & Northern Plains... Days 1-2...

Two shortwave troughs; one heading for the Great Basin and another
over the Northern Rockies, are responsible for the periods of snow
enveloping the higher terrain of the Intermountain West today and
into early Tuesday. The heaviest snowfall (rates between 1-1.5hr
possible) are most likely to unfold along the higher terrain of
the Wasatch, Uinta, and Absaroka through tonight. Snow levels will
generally hover around 7,000ft in UT/NV, around 6,000ft in the
Northern Rockies, and t/above 8,000ft in the CO/WY Rockies. As the
500mb trough over the Great Basin reaches the Central Rockies
Monday night, enhanced vertical ascent aloft will work in tandem
with a surface high building in from the north to foster upslope-
enhanced snowfall over Laramie Range in WY on south into the Park
and Front Ranges of CO. Only light snow will linger over the remote
reaches of the Central and Northern Rockies on Tuesday as the
shortwave troughs exit to the north and east.

WPC probabilities show high chances (>70%) for additional snowfall
totals >4" in the Uinta, Absaroka of southern MT, the CO
Park/Front Ranges, and WY Laramie Range. Snowfall is welcomed
throughout these mountain ranges given the Rockies anywhere from
class 2 (severe) to class 4 (exceptional) drought condition.

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

Mullinax
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 280732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EDT Tue Apr 28 2026

Valid 12Z Tue Apr 28 2026 - 12Z Fri May 01 2026

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

Periods of light-to-moderate snow will linger for a little longer
this morning with an additional 3-6" of snowfall possible in the
Park Range and Flat Tops of the CO Rockies. Snow should taper off
after midday as the shortwave trough responsible for the mountain
snow moves into the Central Plains.

Following a break in the action between Tuesday afternoon and
Wednesday evening, a closed 500mb low (closed at 300mb as well)
west of Baja will head east at the same time that a secondary
impulse over the Great Basin results in 500mb height falls over the
CO Rockies. This "squeeze-play" between the pair of upper-level
troughs and a 500mb ridge over Mexico fosters a robust subtropical
stream, culminating in 200mb winds over the Central Plains that
exceed the 99.5 climatological percentile per ECMWF SATs. In
addition to this textbook jet-streak dynamics setup, high pressure
over the Northern Plains will bleed south down the Front Range and
Sangre De Cristo, forcing favorable easterly upsloping low-level
winds to ensue. This is a classic setup for mountain snow (and
valley/Plains rainfall) in a region that could sorely use any
precipitation of note.

The latest forecast shows snow increasing in intensity along the CO
Front Range throughout the day on Thursday, then along the Sangre
De Cristo Thursday afternoon into Thursday night. There remain some
differences in model guidance regarding the timing and strength of
the approaching 500mb low as it tracks over northern Mexico Friday
morning. Regardless, low-level easterly flow should linger long
enough into Friday to keep mountain snow going through at least the
first half of the day. Most guidance agrees snow tapers off by
Friday evening as the 500mb low races east into the Southern
Plains. WPC probabilities show at least moderate chances (>50%) for
snowfall totals >8" above 9,000ft in the CO Front Range and Sangre
De Cristo, with the Park Range having similar probabilities above
10,000ft. Some of the tallest CO peaks (including Pikes Peak) could
witness localized snowfall amounts surpass 20". Some light snow is
possible over the Palmer Divide and Raton Pass (1-3"), but most
snow is a welcomed sight for drought-stricken CO and NM.

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

Mullinax

$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 010805
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Fri May 1 2026

Valid 12Z Fri May 01 2026 - 12Z Mon May 04 2026

...Southern Rockies... Day 1...

A southern stream upper low south of Arizona is bringing rain to
southern NM/far west TX from convergence along a stalled front
ahead of the low. In the cold sector to the north, sfc high
pressure wedging into northeast NM is aiding lift on the Sangre de
Cristos where snow levels are around 7500ft. The sfc high
strengthens today as a shortwave trough currently over ID shifts
southeast over the Four Corners this afternoon and promotes
instability over the San Juans with snow levels around 8500ft. Day
1 snow probs for >4" additional after 12Z are 40-70% in the San
Juans and NM portion of the Sangre de Cristos. Mountain precip
diminishes late this evening as the shortwave trough axis shifts to
the Plains. across the Central Plains.

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

A large, but overall weak low shifts onshore near the Bay Area
Sunday bringing some moist upslope flow to the Sierra Nevada.
Minor height falls allow Sierra Nevada snow levels to fall from
about 9500ft to 8500ft during the main round of precip Sunday
afternoon. Low precip rates, the high snow levels, and timing
during peak diurnal limits snow to the highest peaks of the
southern Sierra Nevada where Day 3 probs for >2" are around 20%.

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

Jackson
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 030833
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
433 AM EDT Sun May 3 2026

Valid 12Z Sun May 03 2026 - 12Z Wed May 06 2026

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

Broad, not that deep upper low off CA will drift toward the SF Bay
area through tonight, then drift to SoCal through Tuesday when it
opens to a trough and ejects east. Modest moisture plume will
interact with the Sierra Nevada from the south with precip onset
expected this afternoon. Snow levels initially around 9000ft drop
to around 8000ft late tonight. Day 1 snow probs for >6" are around
20% in the High Sierra. The south movement of the low brings
some prolonged flow to the Sierra Nevada with snow levels down to
around 7500ft. Day 2 snow probs for >6" are 40-60% across the High Sierra.

...Wyoming and Colorado... Days 2/3...

Strong ridging north of the CA low will amplify over the northeast
Pacific into the Yukon through tonight and promote troughing to
surge down the Canadian Prairies tonight and the northern Plains
Monday. Meanwhile the SWly jet downstream of the CA low will surge
to the central Plains Monday, aiding left exit dynamics.
Precipitation will expand over southern WY and northern CO Monday
afternoon into Tuesday ahead of the cold front with high snow
levels initially >9000-10,000ft. On Tuesday, the cold front (and
precip focus) will push south through eastern CO with snow levels
lowering to 6000-7000ft behind the boundary that will dam up east
of the Divide, keeping snow levels >8000ft on the west side.
Modest to locally heavier snow should set up over parts of
southern WY through CO via easterly/upslope flow (e.g., Laramie
and Medicine Bow Mountains) with additional modest snow over the
Bighorns and Wind River Range through Tuesday evening before
tapering off as the focus shifts east onto the Plains Wednesday.
Day 2 snow probs for >6" are 20-30% on the Wind River Range and
Bighorns and 30-60% on the south Laramie and CO Front Range. Day 3
snow probs for >6" are nearly identical for the Wind River/Bighorn
with greatly expanded coverage over south WY through central CO
Ranges down to the northern Sangre de Cristos. Probs for >12" are
40-70% along the Front Range in what will be an impactful storm
though should be mainly seen as beneficial/drought relief.

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

Jackson
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)

FOUS11 KWBC 040859
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
459 AM EDT Mon May 4 2026

Valid 12Z Mon May 04 2026 - 12Z Thu May 07 2026

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

Upper low just over SF Bay will drift southeast to southern CA
through Tuesday before opening and ejecting east over AZ Tuesday
night. A modest plume of moisture will intersect the Sierra and
promote light to locally modest snow for the higher elevations as
snow levels remain around 8500ft. Snow will end Tuesday evening as
heights begin to rise. Day 1 WPC snow probabilities for >6" are

50% above about 8500ft.

...Wyoming and Colorado... Days 1-3...

Upper ridging continues to build north of the CA upper low and
extends into the Yukon today, promoting downstream troughing to
surge down the northern Plains through this afternoon. WSWly jet
out of the Pacific subtropics will arc across the Four Corners
region today and provide lift over the cold front that enters CO
tonight. Snow levels of 9000 to 10,000ft will crash behind the cold
front on Tuesday as it shifts southward. Snow levels will lower
over eastern CO to 6000-7000ft as the boundary dams up against east
of the Divide, keeping snow levels >8000ft on the west side.
Modest to locally heavier snow should set up over parts of
southern WY through CO via easterly/upslope flow (e.g., Laramie and
Medicine Bow Mountains) as the upper low pushing into central CA
promotes lee-side troughing on the Rockies and some delay to the
cold frontal passage. Precip shifts down the Rockies through Wednesday
night before shifting east onto the Plains.

Day 1 WPC probabilities for >6" of snow are 40-80% over the
highest Snowy Range in WY and Front Range in CO. Day 2 is the
busiest day with renewed snow in both WY and CO including onto the
High Plains/Denver and snow probs >8" 50-90% over the Front Range
and generally 40-80% for the Wind River, Park Range, Pikes Peak,
and higher portions of the Palmer Divide. Meanwhile snow probs for

4" are 20-40% over the CO High Plains. Day 3 snow probs highlight

the southward shift in the frontal pattern with 30-50% for >8" snow
in the Sangre de Cristos.

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

Jackson
$$
--- MultiMail/DOS
* Origin: Project Scorpio TEST (618:250/6)