FOUS11 KWBC 220831
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
331 AM EST Fri Nov 22 2024

Valid 12Z Fri Nov 22 2024 - 12Z Mon Nov 25 2024

...Pacific Coast through the Interior Northwest and Great Basin... Days 1-3...

Persistent closed low centered off the Pacific Northwest coast will
remain energized by vorticity maxima swinging through the
associated trough this period. This will result in amplification of
the gyre, noted by an expansive region of 500-700mb height
anomalies reaching below -1 sigma, and approaching -3 sigma in the
core of the trough. Beneath this trough, deepening surface low
pressure will approach the WA coast today, but likely get pulled
back to the west on Saturday before landfall in response to
secondary shortwave energy digging to its south. This will result
in persistent onshore and divergent mid-level flow, accompanying
upper level jet energy to spread moisture onshore as a continuation
of the ongoing atmospheric river (AR) across northern CA through
early Saturday. While IVT values exceeding 500 kg/m/s wane and
pivot southward by the end of D1, this will still result in
plentiful moisture and widespread moderate to at times heavy
precipitation pushing onshore the Pacific Coast into the interior Northwest.

Snow levels within this AR will be quite high, generally 6000-8000
ft, except east of the WA Cascades on D1 where they will remain
entrenched around 4000 ft before rising. This indicates that most
of the heavy snow will be above pass levels, except in the higher
Cascade Passes D1, and the Sierra Passes D1-D2. WPC probabilities
D1 are high for more than 6 inches of snow in the northern WA
Cascades, the Salmon River Range, and portions of the Northern
Rockies near Glacier NP. On D2, snowfall is more robust and
expansive, with a greater than 90% chance of 6 inches again in the
Northern Rockies and Salmon River/Sawtooth Ranges. More
impressively, the Sierra will be favorably located to be impinged
upon by moisture by the end of D1, leading to pronounced upslope
snow. WPC probabilities are above 80% for 12+ inches through
Saturday, with 2 feet possible above 8000 ft.

By D2 onward, snow levels crash again as a cold front pushes
onshore, but this is accompanied by reduced moisture advection as
the column begins to dry out. Some moderate snow will persist
through onshore flow, especially in the Sierra where an additional
6-12 inches is possible, but otherwise WPC probabilities for more
than 6 inches are between 30-50% and focused across the Wasatch,
Uintas, and ranges of NW WY.

...Appalachians and Northeast... Days 1-2...

Impressive upper low over the Northeast will feature a complex
evolution through the weekend resulting in a couple surface lows and
varying areas of heavy snow.

The Central Appalachians, especially from the Laurel Highlands
southward across WV and as far south as the Great Smokey Mtns of
TN/NC, will benefit from prolonged upslope flow on the western
periphery of the upper low resulting in waves of heavy snowfall
through Saturday. WPC's snowband probability tracker depicts an
extended period of 1-2"/hr snowfall rates during the D1 period
across the Allegheny Mtns. WPC probabilities in this area are high

70%) on D1 for more than 8 inches of snow. Event total snowfall

could peak around 2 feet in central WV.

The ongoing potent and compact surface low churning near Long
Island is forecast to loop westward and eventually toward the south
today over eastern PA as it remains embedded within the large
500mb gyre overhead. As this occurs, an impressive plume of low-
level moisture will continue to wrap northwest into the system,
driving rich theta-e advection into a TROWAL to support some
elevated instability and enhance available moisture for heavy
precipitation early on D1. Increasing deformation is noted on
current radar trends on the W/SW side of the system as it becomes
exceptionally wrapped. This setup will support intense mesoscale
ascent and bands of heavy precipitation rotating W/SW as the low
retrogrades. Although the column will be marginally supportive of
accumulating snow outside of higher elevations (above about 1500
ft), the intense lift should dynamically cool the column and allow
efficient snowfall accumulation at times even in lower terrain.
SLRs for this event will likely be below climo due to near freezing
temps and warm soils/compaction, but still, rates of 1-2"/hr will
promote heavy accumulations, especially in the Poconos and
Catskills and surrounding areas early this morning. Most of the
ongoing snowfall is expected to occur before or right around the
start of the D1 period (12z Fri), so WPC probabilities don't
reflect the ongoing event. Nonetheless, the greatest snowfall
amounts are expected in northeast PA and neighboring areas of New
York and northern NJ, with 2-day snowfall potentially reaching
above 12" in a few highly elevated spots. This will likely result
in dangerous travel and impacts to infrastructure including
scattered power outages.

In the lower elevations of the Mid-Atlantic, some snow bands could
pivot as far SE as the I-95 corridor, so while accumulations in
the major urban areas from Washington, D.C. to New York City are
expected to be minimal, if any, these cities could see their first
"falling" snow of the season Friday morning/aftn.

Along the Adirondacks, Green, and White Mountains, the
upper low will draw moist easterly flow northward and into these
ranges Friday night through Saturday while another surface low
develops east of Maine and pivots northwest. Snow levels should be
high enough that only the highest terrain will receive significant
snow, but WPC probabilities have increased and now feature a 30-50%
chance on D2 of more than 4 inches, primarily in the White
Mountains of NH and the peaks of northern ME.

...Northern Rockies through the Northern Plains... Days 1-2...

A shortwave ejecting through the base of an anomalous trough off
the Pacific Coast will swing eastward into the Northwest Saturday
and then begin to amplify into a potent but fast moving impulse
across the Northern Rockies and into the Northern Plains Sunday.
This deepening system will drive downstream ascent through height
falls, PVA, and divergence. At the same time, a zonally oriented
jet streak will pivot south of the region, placing its favorable
LFQ atop the far northern High Plains, interacting with increasing baroclinicity as a front wavers near the international border. The
overlap of synoptic lift with the enhanced mesoscale ascent
through fgen will result in weak cyclogenesis, leading to an
expanding area of precipitation falling as snow. The column will be
plenty cold for wintry precipitation thanks to high pressure from
Canada extending southward, and as the WAA along the warm front
lifts north, it will result in an exceptionally deep DGZ to support
fluffy aggregate dendrites which should accumulate efficiently. The
biggest question remains whether or not this favorable environment
and most impactful snowfall will span south over the U.S.-Canada border.

The heaviest snowfall is likely in the terrain near the Northern
Rockies where upslope flow will enhance ascent, and WPC
probabilities support a high risk (>70%) for at least 8 inches near
Glacier NP on D2. However, heavy snowfall is also possible farther
east across northern MT along the international border D1-D2 where
the most robust synoptic ascent will materialize. A leading surge
of modest upper diffluence and WAA may lead to a burst of snow
today across northwest and northern MT. WPC probabilities for at
least 2" on D1 are high throughout northern MT. For the main
activity related to the approaching shortwave on D2, the guidance
has continued to trend a bit farther north from central MT eastward
to ND, with current WPC probabilities suggest around a 30% chance
for more than 4 inches right along the international border as far
east as north- central MT on D2, with higher probabilities for
heavy snowfall located in southern Alberta and Saskatchewan.

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

Snell

...Winter Storm Key Messages are in effect. Please see current
Key Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

$$
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FOUS11 KWBC 140817
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
317 AM EST Sat Dec 14 2024

Valid 12Z Sat Dec 14 2024 - 12Z Tue Dec 17 2024

...Western U.S...

An active period will bring widespread winter weather to much of
the West through early next week.

A large trough just offshore the Pacific Coast to start the period
will shed two distinct compact vort maxima/shortwaves onshore on
D1. One of these will pivot northward into British Columbia, while
the second one ejects into central CA. Although the northern
impulse is a bit deeper relative to the CFSR climatology (500mb
heights below the bottom 2.5 percentile according to NAEFS), the
greater moisture/IVT will pivot into CA associated with the
southern system as the northern moisture channel lifts into Canada. Additionally, there will be a modestly coupled jet streak
downstream of the primary trough axis and in the vicinity of this
southern impulse, helping to enhance ascent to spread more
widespread moisture northeast. On D1, this will cause widespread
heavy snow from the Sierra and Shasta/Trinity region eastward into
the Salmon River/Sawtooth Ranges, Blue Mountains, and as far east
as the Tetons and Big Horns, WPC probabilities are high (>70%) for
above 12 inches in the CA ranges and into ID thanks to higher
moisture, strong synoptic lift, and impressive upslope flow driving
snowfall rates of 2+"/hr at times. 1-2 feet of snow is possible D1
across these areas.

More modest snowfall across the WA/OR Cascades and Olympics where
both ascent and moisture are more limited. Still, WPC probabilities
in the Cascades and Olympics are moderate to high (50-90%) for
more than 8 inches. Snow levels D1 will climb briefly to as high as
5000-6000 ft in the core of the max IVT/WAA/moisture plume, but
will fall gradually most of the day to as low as 2000 ft in the
Cascades and 3500 ft elsewhere. This will allow at least modest
accumulations below pass levels, but most of the accumulating snow
is likely during the period of higher snow levels.

On D2, the pattern evolves quickly as a narrow but amplified
longwave ridge builds over the Pacific Coast, forced between the
departing trough now moving into the northern High Plains and a
renewed closed low back over the Pacific Ocean. This will force a
respite in precipitation across the coast and into the Great Basin,
but wintry precipitation will continue into the Northern Rockies,
but in a slowly waning fashion. Snow levels will continue to fall
steadily D2, reaching below 1000 ft in the Northern Rockies, which
coincident with continuing (but easing) snow will result in heavy
snow accumulations across the NW WY ranges, with some light
accumulations down into most of the valleys. WPC probabilities D2
are moderate (50-70%) for an additional 6+ inches, highest in the Tetons.

Late D2 and then more substantially into D3, the large closed low
west of WA/OR will spin two distinct vorticity maxima/shortwaves
onshore, leading to increasing waves of precipitation spilling
eastward once again. With this next impulse, snow levels will
initially be low, only around 1500 ft, with modest rising
occurring in the axis of greatest IVT. Despite IVT progged to
remain only around 250 kg/m/s, this will lift snow levels to around
3500 ft west of the Cascades in WA/OR, and then potentially as
high as 4500 ft later D3 with the second wave. With impressive
ascent increasing, and upslope flow amplifying into the terrain,
heavy snowfall will result, and WPC probabilities D3 are moderate
(50-70%) for 6+ inches from the Shasta/Trinity region northward
along the Cascades.

Moisture spilling east into the interior Northwest will encounter
some trapped cold air and modest easterly flow ahead of the
accompanying WAA/IVT, such that some light freezing rain could
result on the eastern side of the Cascades. Potentially more
impressively, the accompanying WAA and associated fgen could result
in heavier snow rates farther east which could reach the valley
floors of interior WA and OR. Confidence is low this far out, but
WPC probabilities do indicate at least a low chance for 1" of snow
across much of WA east of the Cascades, with heavier snow likely
moving back into the Salmon River/Sawtooth Ranges before the end of
the period.

...Central Plains into the Upper Midwest... Day 1...

A mixed snow, sleet, and freezing rain event will be ongoing to
start the forecast period as a wave of low pressure moves steadily
from Kansas into the western Great Lakes. This low will be driven
by a compact but potent closed low moving over-top the surface
low, with downstream warm and moist advection expanding the
precipitation shield northeast through the region. As this
vertically stacked system moves east, it will run into some cold
and dry antecedent air as an expansive high pressure gradually
retreats towards New England. As WAA intensifies, it will push a
warm nose above 0C, while surface wet-bulb temperatures will remain
below freezing. The guidance has narrowed the corridor of
significant freezing rain, and despite what could be moderate
precip rates (supported by soundings) and a lack of dry advection
to offset latent heat release of freezing (and to prevent
substantial warming), there is high confidence in a stripe of
significant ice accretion, especially in eastern and central IA.
Here, WPC probabilities are moderate (50-70%) for an additional
0.1+ inches of ice, leading to local event totals exceeding 0.25".

...Central Appalachians... Days 1-2...

Sprawling high pressure with impressive central pressure
approaching 1050mb will gradually pivot east through New England
during the weekend. While this feature will retreat, it will extend
down the coast east of the Appalachians as a cold-air damming
scenario, at least initially reinforced by mid-level confluence
ahead of an approaching shortwave. This impulse will lift from the
Corn Belt late Saturday to off the New England coast, with the
associated moisture and ascent producing a swath of precipitation
extending from the Southern Appalachians through southern New
England. The WAA overrunning the cold surface layer will likely
result in an axis of moderate to heavy freezing rain in the higher
elevations from southern WV through the MD Panhandle and into the
Laurel Highlands where WPC probabilities for more than 0.1 inches
of ice reach as high as 70%, and locally in excess of 0.25" is
possible near the MD Panhandle and into the southern Laurel
Highlands which is where the greatest duration of freezing rain is
expected. Surrounding this, light freezing rain could result in
accumulating ice exceeding 0.01 inches as far south as the northern
escarpment of SC, and as far north as some of the higher terrain of
Upstate NY.

While the most significant winter impacts are likely due to
freezing rain, many areas from PA through MA will experience
precipitation at least starting a snow with some light
accumulations likely in the higher elevations of the Poconos,
Catskills, and Upstate NY/western New England. At this time
however, WPC probabilities are only 50-70% for 2+ inches in these
areas. In places that receive mostly rain, a brief mix of snow and
sleet is possible during precipitation onset even as far southeast
as the I-95 corridor, but no accumulation is expected.

...Northern Plains... Days 2-3...

Vorticity maxima leftover from a weakening shortwave will lift
northeast from the Great Basin, with secondary intensification of
this feature likely over eastern MT Sunday. The guidance has
continued to trend a bit deeper and farther south with this
secondary development, suggesting a higher potential for some
moderate to heavy precipitation from MT into ND.

As the lead shortwave weakens and pushes northeast, some leading
WAA will expand light precipitation into the northern High Plains.
Forecast soundings suggest considerable dry air to overcome, but
as this occurs it will cause some wet-bulb effects to keep temps
below freezing and an axis of light freezing rain is likely from
eastern MT into western ND Saturday night into Sunday morning.
Accumulations are likely to be modest, however, as reflected by WPC probabilities for 0.1+" of ice peaking around 30% in eastern MT on
D2. Still, any freezing rain can cause hazardous travel
conditions.

Thereafter, the secondary impulse deepens into a closed low which
should cause some enhanced deformation to the north and west of the
system. This deformation acting upon some higher theta-e air
wrapping cyclonically around the low (emerging from intensifying
290K isentropic ascent downstream) will support some banded snow
rotating through ND and then into MN Sunday night and Monday. At
this time total snowfall is still expected to be light however,
with WPC probabilities for 2+ inches of snow reaching just around
50% from eastern ND into northern MN.

Weiss
$$
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FOUS11 KWBC 090835
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EST Sun Feb 9 2025

Valid 12Z Sun Feb 09 2025 - 12Z Wed Feb 12 2025

...Great Lakes and Northeast...
Days 1-2...

A significant winter storm will wind down this morning across New
England as an area of low pressure pulls away from southern New
England leading to rapid drying and renewed CAA. Light snow should
finally come to an end along coastal regions by about 16z or so.
However, the CAA behind the accompanying cold front will setup an
environment favorable for LES E/SE of Lake Ontario and SE Lake
Superior. Shifting winds (more N/NW early, becoming more W D2 and
weakening by D3) will result in a shifting band of LES. Latest
Great Lakes ice analysis shows Lake Ontario remaining mostly ice
free with surface water temperatures around 3 to 4 degrees C. For
D1, the most significant accumulations are likely in the northern
Finger Lakes region, where they have a 70-90% chance of exceeding
4" near the lake shore, with D3 probabilities for 4+ inches
reaching 50-70% focused in the Tug Hill Plateau. Additionally,
probabilities for 4+ inches are 30-50% D1-2 across the Keweenaw
Peninsula and near Whitefish Point in the U.P. of MI.


...Central Plains through the Mid-Atlantic...
Days 2-3...

The next in this parade of systems across the CONUS begins to
develop D2/Monday as a shortwave trough ejects from near Baja and
then moves east into the Southern Plains by Tuesday evening. This
shortwave will remain embedded within a longwave trough axis as it
moves east through its evolution, but 00z guidance has trended
slightly more amplified with the longwave pattern. This subtle change
can be traced to a more consolidated western trough and faster Pac
NW shortwave that pumps up the eastern U.S. ridge ever so slightly
in order to prompt more southwesterly upper flow as opposed to
straight zonal winds. This trend, should it persist, would give the
impressive IVT (up to the 97.5th climatological percentile per the
12z NAEFS) the ability to bring the precipitation shield a bit
farther north across the Ohio Valley and Mid-Atlantic, where snow
is the dominant ptype. Additionally, upper diffluence will likely
increase with time as a downstream jet streak intensifies towards
150kts and arcs sufficiently poleward while leaving its tail across
the Central Plains and into the Lower MS VLY by Tuesday evening.
This will provide additional deep layer ascent as the system
organizes over the Mid-Atlantic through D3 and promoting a longer
duration moderate to heavy snowfall. Snow ratios for a majority of
the event are expected to remain around climo or slightly below
(8-11:1) due to an elevated DGZ and strong winds through it. So,
the main question remains how far north and how heavy QPF is should
the more amplified trend continue.

Light snow is expected to develop first across the central Plains
and Mid-Mississippi Valley on D2 as the upper jet begins to
intensify over the central U.S., which then begins to quickly
expand eastward into the Mid-Atlantic and central Appalachians on D3.

WPC probabilities at this time for snowfall are highest for 4+
inches in the higher elevations of WV/VA where they peak above 70%,
and locally 6+ inches of snow is possible. Elsewhere, WPC
probabilities for 4" have increased and reach 40-60% across
central/northern VA, MD, and DE. Probabilities for at least 2" are
low 10-20% across the central Plains and Mid-Mississippi Valley,
but increase to above 70% across eastern KY and western WV.

There also exists the potential for an area of mixed ptype
associated with this system, one over the Ozarks of AR and a more
impressive area extending from western NC to southwest VA. The set
up supports a potentially significant ice storm in the Piedmont
and Foot Hills of the central/southern Appalachians where a
classic CAD setup and overrunning precip combine to create an
environment ripe for freezing rain. Large high pressure spanning
across the northern and eastern U.S. through Tuesday will
consolidate and reposition over southern Quebec by early Wednesday.
As a constant flow of precipitation remains aimed at the southern
Appalachians, cold northerly flow at the surface also continues
along and just east of the Blue Ridge Mts. while modest mid-level south-southwesterly flow brings the warm nose into central VA. As
a result, WPC probabilities for at least 0.25" of ice have
increased to around 20-40% from northwest NC to much of southwest
VA east of the continental divide. Additional freezing rain is also
likely during the period following D3, with moderate- level WSSI-P
values up to 40-60%. Lower probabilities of 10-30% for at least
0.1" of ice exist across the AR Ozarks.


...Central Rockies and Central Plains...
Day 3...

Another winter storm will quickly develop by the end of D3 (Tuesday
night) across the central Rockies/Plains as the aforementioned long
wave trough over the West begins to lift northeastward due to
interacting shortwaves initially over the Northeast and near
northern Baja California. This interaction reinvigorates the
extended and strong jet streak arching from the Mid-Mississippi
Valley to New England, prompting optimal upper diffluence in the
central Plains. At the surface, large high pressure up to the 99th climatological percentile per the 12z NAEFS will supply cold air
throughout much of the Plains and a cold front well south to the
Southern Plains. Thus, forcing will be mostly elevated and for the
northern parts of the precipitation shield a very deep DGZ (over
300 mb for parts of KS, NE, and IA Monday morning per the 00z GFS)
and very light winds could support snow ratios well above climo.
WPC probabilities through the end of the forecast period (12z
Wednesday) reach above 70% in the highest terrain of the CO Rockies
and are 40-70% for much of western and central KS, with the
majority of snowfall expected from this event after 12z Wednesday.


Snell

$$
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FOUS11 KWBC 070706
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
206 AM EST Sat Feb 7 2026

Valid 12Z Sat Feb 07 2026 - 12Z Tue Feb 10 2026

...Northeast & Mid-Atlantic... Day 1...

Extreme cold and dangerous wind chills overspread the Northeast
tonight and continue through Sunday with Key Messages in effect
and linked below.

The combination of an arctic cold front current racing through the
Ohio Valley/Interior Mid-Atlantic will combine with a strengthening
low pressure well offshore to produce extremely cold temperatures
and damaging winds for much of the region, with heavy snow for
parts of the area as well.

A shortwave driving the cold front southward will help generate
widespread light snow across New England and Long Island, but total
snowfall amounts are expected to be rather modest. Despite that,
briefly heavy snow rates combined with the rapidly increasing winds
will still result in impacts, especially to travel due to snow-
covered roads and low visibility. The greatest impacts, and likely
more substantial snowfall, is expected from far SW Maine, SE New
Hampshire, and along the eastern Coast of Massachusetts from Cape
Ann to Cape Cod where low-level convergence, onshore flow and
resulting ocean effect snow (OES) and an inverted trough will all
interact to enhance snowfall. There continues to be uncertainty as
to where the heaviest snowfall will occur. However, intense
snowfall rates of 1-2"/hr are possible (30-60% chance) thanks to
intense ascent into a lowering DGZ within the presence of some
instability. WPC probabilities are moderate (50-70%) for 4+ inches
from the Seacoast of NH through the Boston metro area, with locally
more than 8 inches possible (10-30% chance) and as reflected by
significant spread amongst the WSE plumes.

...Pacific Northwest and Northern Rockies... Days 1-3...

Mid-level trough positioned off the Pacific coast will slowly track
eastward today and Sunday, with the primary trough axis finally
pushing onshore Sunday night as a shortwave lifts onshore near the
CA/OR coast. This shortwave will then continue to track east while deamplifying, reaching the northern High Plains by the end of the
forecast period.

This trough evolution will be accompanied by a modest subtropical
jet streak arcing meridionally downstream to provide overlapping
synoptic ascent. This lift will occur into a moistening column as
persistent SW flow ahead of the shortwave/trough axis will provide
a long duration of IVT exceeding 250 kg/m/s, with IVT max
potentially exceeding 500 kg/m/s (50-60% chance) which will lead to
two rounds of heavy precipitation extending from Oregon through
the Northern Rockies. Snow levels within the strongest IVT plume
will be 6000-7000 ft thanks to pronounced WAA, but will steadily
fall to 3000-4000 ft Monday as a cold front, driven by the
aforementioned trough, progresses southeast. This will allow for
heavier and more impactful snow across the Northern Rockies than
what is anticipated in the Cascades due to lower snow levels. 2-day
WPC probabilities indicate the heaviest snow is expected in the
vicinity of Glacier NP in the Northern Rockies where they exceed
70% for 12+ inches, and locally as much as 2 feet is possible in
the highest terrain. Elsewhere, WPC probabilities are high (>70%)
for 8+ inches across the Absarokas and Tetons near Yellowstone NP,
the Blue Mountains of OR, and across the highest peaks of the WA
and OR Cascades.

Weiss

...Extreme Cold Key Messages are in effect. Please see current Key
Messages below...

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_1.png

$$
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FOUS11 KWBC 140832
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EST Sat Feb 14 2026

Valid 12Z Sat Feb 14 2026 - 12Z Tue Feb 17 2026

...Cascades... Days 1 & 3...

A broad upper-level troughing pattern off the Pacific NW coast
will continue to supply lingering low-mid level moisture that
allows for light snow through this morning. Snow levels will drop
to as low as 2000-3000ft today and into Saturday evening, bringing
snow to many of the passes over the WA Cascades. Following a lull
in snowfall Saturday night and into Sunday, another surge of
moisture will be supplied by a strengthening 500mb closed-low west
of British Columbia. Sharp height falls and excellent 500mb PVA
will be paired with an influx of 850-300mb mean-layer moisture to
produce periods of snow. Snow levels will plummet to as low as
800ft around the WA Cascades, while 2000 ft snow levels in the OR
Cascades will be more common. While these snow levels are getting
quite low, snowfall totals below 2,000ft in the WA/OR Cascades will
remain light. The heaviest snowfall will reside above 3,000ft
72-hour WPC probabilities show moderate chances (40-60%) for
snowfall totals >4" for both Snoqualmie Pass and Stevens Pass.
Given the long duration but lack of heavy hourly rates, WSSI-P
shows the chances for Minor Impacts are generally on the low side
(20-40%) with Monday having the best chances for some slick travel
conditions at pass level.

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

...Multiple days of heavy and disruptive snowfall to affect the
California mountain ranges beginning Sunday and continuing into next week...

A pair of potent Pacific storm systems will work together to direct
copious amounts of moisture at the mountain ranges of the "Golden
State" starting Sunday. The first upper low west of California will
kickoff this multi-day heavy snow event on Sunday with snow falling
in the higher terrain of the Siskiyou, Shasta, and Salmon
Mountains. By Sunday night the upper low approaches, causing
heights to fall over CA and the strengthening IVT to direct
subtropical moisture at the state. Monday marks the beginning of
heavy snowfall along the Sierra Nevada with snow levels will
generally ranging from 4500ft to 6000ft from north to south
initially, then fall below 3000ft across northern CA as the other
potent Pacific trough approaches from the northwest. In both cases,
the state will be placed ahead of a pair of 500mb jet streaks that
will generate excellent upper-level divergence aloft, along with a
barrage of Pacific moisture and strong topographically-enhanced
snowfall rates. Heavy snowfall is expected as far south as the
Transverse Ranges above 6,000ft with WPC probabilities showing
moderate chances (40-60%) for snowfall totals >8" in the peaks of
the San Gabriel and San Bernadino Mountains.

California's mountain ranges welcome the snow, although it will
come down fast and furious on Monday and continue into Tuesday.
Through the end of this discussion's timeframe (12Z Tues), multiple
feet of snow will have fallen above 6,000ft along the Sierra
Nevada. WPC probabilities show high chances (>70%) for >24" of
snow having fallen along the I-80 pass by 12Z Tuesday and more snow
still to come. The WSSI-P depicts a highly impactful snow event
along the Sierra Nevada with high chances (>70%) for Major Impacts
above 6,00ft, including the I-80 pass. In fact, for the higher
elevations above 8,000ft, the WSSI-P shows moderate chances (>50%)
for Extreme Impacts, suggesting the potential for significant
impacts to infrastructure. Travel will be dangerous to impossible
in the Sierra Nevada into Tuesday. Note that there are also high
chances (>70%) for Minor Impacts for I-5 around Mount Shasta,
signifying potential travel delays for I-5 in the more elevated
terrain of northern CA.

...Intermountain West... Days 1-3...

Pacific moisture ahead of the longwave upper trough off the West
Coast will spill over the Cascades and Sierra Nevada and reach many
ranges across the Intermountain West this weekend and into early
next week. With a lack of a frigid airmass ahead of this healthy
moisture source, snow will largely be confined to many of the
taller mountain peaks that sorely need beneficial snowpack. The
heaviest snowfall will reside in the Bitterroots, the Lewis Range,
Sawtooth, and the Blue Mountains whee 72-hour WPC probabilities
show moderate-to-high chances (50-80%) for snowfall totals >8".
Localized amounts ranging between 12-24" are most likely to occur
along the remote reaches of the Lewis Range and peaks of the Blue
Mountains. Farther south, most accumulations in the Great Basin,
the Wasatch, Uinta, Mogollon Rim, and CO/NM Rockies will be on the
lighter side. The peaks around Zion Nat'l Park on north along the
Wasatch sport moderate-to-high chances (50-70%) for snowfall totals

4". Otherwise, most mountain ranges are likely to see 1-4" of

snowfall, with additional snowfall still to come on Tuesday.

...Northeast... Day 2...

The last 24 hours have seen some model guidance (GFS/ECMWF)
gradually creep north with the precipitation shield. This is due to
the approaching 500mb shortwave over western PA coming in
stronger, thus leading to healthier PVA aloft and more 250mb jet
streak enhancement aloft. While boundary layer temperatures along
I-95 south of Philadelphia remain quite marginal on Sunday,
elevated terrain north and west of the Delaware River are likely to
have better chances to see wet snow Sunday afternoon. As the upper
trough in the Carolinas spawns low pressure over the NC Outer
Banks Sunday evening, 850-700mb WAA to the north of the low will
support narrow banding of snow from eastern PA and northern NJ to
the NYC metro, Long Island, and coastal southern New England. There
remains notable spread in model guidance in the position of this
band, but trends in not only the GFS/ECMWF guidance but also their
AI counterparts are showing additional support for a ribbon of
light snow. WPC probabilities show low-to-moderate chances (30-50%)
for snowfall totals >1" from the Delaware and Lehigh Valleys on
east to Long Island, but probabilities for >2" of snowfall are
<20%, showing that most totals are minor and likely to range
between a coating-2". There is the potential for additional
changes to this forecast in the next 12-24 hours.

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

Mullinax

$$
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FOUS11 KWBC 150732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
232 AM EST Sun Feb 15 2026

Valid 12Z Sun Feb 15 2026 - 12Z Wed Feb 18 2026

...Cascades & Olympics... Days 2-3...

On Monday, a strengthening 500mb closed-low west of British
Columbia will slide south and just off the coast through Tuesday.
Sharp height falls and excellent 500mb PVA, combined with an
influx of 850-300mb mean-layer moisture and upslope enhancement,
will produce periods of snow over the Olympics and Cascades. Snow
levels will plummet to as low as 800ft around the WA Cascades and
Olympics, while 2000ft snow levels in the OR Cascades will be more
common. In fact, some of OR's coastal range could see snow to
elevations as low as 1,000ft. While these snow levels are getting
quite low, snowfall totals below 2,000ft in the WA/OR Cascades will
remain light. The heaviest snowfall will reside above 3,000ft
where 72-hour WPC probabilities remain in the moderate range
(40-60%) for additional snowfall totals >4" for both Snoqualmie
Pass and Stevens Pass. Given the long duration but lack of heavy
hourly rates, WSSI-P shows the chances for Minor Impacts are
generally on the low side (20-40%). Impacts are most likely to be a
combination of snow covered roads and reduced visibilities.

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

...Multiple days of heavy and disruptive snowfall to affect the
California mountain ranges beginning Sunday and continuing into next week...

A pair of potent Pacific storm systems will work together to direct
copious amounts of moisture at the mountain ranges of the "Golden
State" beginning today and lasting into the middle of the upcoming
week. A broad positively-tilted upper level troughing pattern off
the Pacific NW coast will supply low-mid level moisture that
allows for light snow through tonight into the higher terrain of
the Siskiyou, Shasta, and Salmon Mountains. The heaviest snowfall
through Sunday are likely to reside above 5,000ft where 1-2 feet of
new snow accumulation are possible at the higher elevations
through Sunday night.

By Sunday night, the upper low approaches, causing mid-to-upper
level heights to fall over CA and the strengthening IVT to direct
subtropical moisture at the state. The state will be placed ahead
of a 500mb jet streak that will generate excellent upper- level
divergence aloft, along with a barrage of Pacific moisture and
strong topographically-enhanced snowfall rates. Monday marks the
beginning of heavy snowfall along the Sierra Nevada with snow
levels initially starting out around 6,000ft from north to south
initially, then falling to as low as 3,000ft by Monday night.
Farther north, snow level will dip below 3,000ft across northern CA
as the other potent Pacific trough approaches from the northwest.
Snowfall rates between 1-2"/hr will be common with some instances
of >3"/hr snowfall rates in the central and southern Sierra
Nevada. Heavy snow is also expected in the Transverse Ranges above 6,000ft.

By Tuesday, another round of heavy snow is expected across just
about all of the CA mountain ranges as a second, strong upper
level low dives south along the West Coast, enhancing onshore flow
and supplying additional moisture on the southern and eastern
flanks of the upper low. Snow levels will fall to around 1,000 ft
in far northern California (including the northern coastal range),
around 2,500ft in the Sierra Nevada, and just below 5,000 ft into
the Transverse Ranges with snow continuing to fall across the
state's mountain ranges into Wednesday.

California's mountain ranges welcome the snow, although it will
come down fast and furious both Monday and Tuesday. Through the
end of this discussion's timeframe (12Z Wed), multiple feet of
snow will have fallen above 5,000ft along the Sierra Nevada. WPC
probabilities show high chances (>70%) for >30" of snow having
fallen along the I-80 pass by 12Z Wednesday and more snow still to
come. The WSSI shows a large swath of Extreme Impacts (Substantial
disruptions to daily life; extremely dangerous travel or impossible
driving conditions, extensive closures) for elevations generally
above 6,000ft, although some Extreme impacts as low as 5,000ft are
possible. Major to locally Extreme impacts are showing up in the
peaks of the San Gabriel and San Bernadino mountains, with mostly Moderate-to-Major Impacts (increasingly more disruptive to travel
jumping from Moderate to Major). Note that there are also Minor to
locally Moderate Impacts along I-5 around Mount Shasta, signifying
potential travel delays for I-5 in the more elevated terrain of northern CA.

...Intermountain West... Days 1-3...

Pacific moisture ahead of the longwave upper trough off the West
Coast will spill over the Cascades and Sierra Nevada and reach many
ranges across the Intermountain West today and into the upcoming
week. With a lack of a frigid airmass ahead of this healthy
moisture source, snow will largely be confined to many of the
taller mountain peaks that sorely need beneficial snowpack. The
heaviest snowfall will reside in the Bitterroots, the Lewis Range,
Sawtooth, and the Blue Mountains where Farther south, most
accumulations in the Great Basin, the Wasatch, Uinta, Mogollon Rim,
and CO/NM Rockies will be on the lighter side. The peaks around
Zion Nat'l Park on north along the Wasatch sport moderate-to-high
chances (50-70%) for snowfall totals >4". Otherwise, most mountain
ranges are likely to see 1-4" of snowfall through Monday.

On Tuesday, the highly anomalous upper-low off the Pacific NW coast
will help to usher the initial upper low over southern CA east into
the Intermountain West, causing widespread height falls and a
larger footprint of Pacific moisture to track through the Rockies.
Snow levels will lower to the valley floors in western Mt and
northern ID, with some light snow possible even in the Salt Lake
City area. Still, the lack of a frigid airmass at the surface will
keep the bulk of the heavy snow in the mountains with ranges such
as the Wasatch, Bear River, Tetons, Uinta, and Wind River seeing
locally heavy snowfall along their peaks. Many of the CO ROckies
will also receive snowfall, but the heavier amounts >8" will be
confined to elevations above 9,000ft.

72-hour WPC probabilities show high chances (>70%) for snowfall
totals >8" for most of the Intermountain West's ranges, but the
locally heavier total's (>12") are most likely to occur in the
peaks of the Lewis Range, the Bitterroots, Sawtooth, Blue, Bear
River, Wasatch, and Uinta.

...Upper Midwest & Great Lakes... Day 3...

By 12Z Tuesday, the remnant yet vigorous trough that was originally
over southern CA late Monday will race across the Rockies and
project excellent 500mb PVA over the northern High Plains. The
ECMWF SATs shows a roaring 150kt 200mb jet streak (wind speeds
topping the 99.5 climatological percentile) over the Southwest will
place its divergent left-exit region over the Great Plains. With
the aid of lee-side downsloping and low-level WAA across the
Plains, an exceptionally deep surface low will form over southern
MT that reaches as low as 980mb Tuesday morning, or MSLP values
that are below the 1st climatological percentile. As WAA ahead of
the warm front reaches across the Upper Midwest, strong isentropic
ascent will ensue as the warm/moist air runs into a colder/drier
air-mass over northern ND and northern MN. Precipitation initially
starting as rain Tuesday afternoon will changeover to snow over
northeast MT, northern ND, and as far east as the MN Arrowhead
Tuesday night. Meanwhile, from northern MN and northern WI to the
northern tier of Michigan's Mitten, the overrunning setup would
favor a wintry mix of sleet and freezing rain Tuesday night and
into Wednesday morning. WPC probabilities show low chances (10-30%)
for pockets of over one-tenth of an inch of ice accretion in parts
of northern WI and MI.

There remains a high degree of uncertainty in the storm track, as
well as when the transition to snow would occur. Snow beneath the
strengthening TROWAL over northeast MT and northern ND would
perhaps not only support heavy snow, but the impressive strength of
the cyclone itself would foster blowing snow on its northern and
western flanks.In terms of snowfall, the MN Arrowhead sports low-
to-moderate chances (30-50%) for >4" of snowfall through 12Z Wed.
Most of far northeast MT, northern ND, and northern MN have
moderate chances (40-60%) for >2" of snowfall, but this is an area
where any minor change in duration or placement in the deformation
axis could result in notable changes to the snowfall forecast.
Regardless, the pressure gradient will be tight enough to where all
of these areas have moderate chances (40-60%) for Minor Impacts
(per WSSI-P) due to some combination of snowfall amounts of blowing
snow through early Wednesday morning.

...Northeast... Day 1...

The airmass in the northern Mid-Atlantic and latest guidance
continues to favor areas farther north from southeast PA across
the Delaware River and into NJ and as far east as Long Island for
light snowfall. WPC probabilities show low-to moderate chances
(30-50%) for snowfall totals >1" from the Delaware and Lehigh
Valleys on east to Long Island, but probabilities for >2" of
snowfall are <30%, indicating that most totals are minor and
likely to range between a coating-2" from southeast PA (with
elevation) on east through northern NJ and across the NYC metro.
Snow should peak in intensity Sunday night and conclude by Monday morning.

Mullinax
$$
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