FOUS11 KWBC 110852
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
352 AM EST Tue Feb 11 2025

Valid 12Z Tue Feb 11 2025 - 12Z Fri Feb 14 2025

...Ohio Valley to the Mid-Atlantic... Days 1-2...

Active pattern continues with two significant winter weather
events progged to impact the area with different hazards through
Wednesday night.

The first is already taking shape across the Mid-Mississippi and
Ohio valleys this morning as precipitation begins to expand from
the Ozarks to the southern Appalachians, with snow and a wintry mix
expected to stretch from near southern IL to southwest VA by the
start of D1 (12z/Tues). This precipitation shield will be the
result of an overlap of forcing and moisture expanding into the
region from the west and south. A shortwave trough and accompanying
vorticity maxima is racing eastward across the Southern Plains this
morning while also weakening in response to confluent/flat flow
across the eastern CONUS. Despite the modest amplitude of this
feature, ascent will intensify through modest PVA and mid-level
divergence overlapped with the right entrance region to a jet
streak amplifying to the northeast. A weak surface wave may develop
and skirt almost due east ejecting off the Mid-Atlantic early
Wednesday, but in general precipitation will be driven by the
overlap of the synoptic ascent and increasingly impressive moist
isentropic upglide/WAA emerging from the Gulf.

The moisture surging northward will be significant as reflected by
mixing ratios within the robust 290-295K isentropic ascent
reaching as high as 6-8 g/kg, drawing PWs as high as the 90th
climatological percentile as far north as southern VA. This
moisture flowing northward overrunning the cold airmass in place
from the Ohio Valley to Mid-Atlantic will lead to an expanding
swath of precipitation, with rounds of heavier rates likely
embedded near where mid-level fgen is strongest. There remains some
uncertainty with respect to the northern edge of the heaviest QPF,
mainly due to dry air intrusion and if the strengthening WAA can
overcome it. This will lead to a sharp northern gradient along the
Mason-Dixon Line and into central NJ. Marginal surface temperatures
at onset during the day will also limit snowfall accumulation. However,
there is high confidence that a stripe of heavier snowfall rates
overcoming these marginal surface temperatures will spread east
from Kentucky through Delaware. Snowfall rates of 1+"/hr are likely
at times, especially within the west-to- east oriented fgen band
progged to start in eastern KY this morning and central VA by the
afternoon before weakening and gradually lifting northward into
southern MD and the Delmarva Peninsula. This is in conjunction
with where 850-700mb fgen maximizes ascent and occurs in
conjunction with CSS (EPV* < 0.25) to support CSI. Where this band
develops, locally higher amounts of snow are possible, but in
general WPC probabilities spanning D1 and early D2 are high (>70%)
for more than 4" from eastern KY though the Central Appalachians
eastward to southern MD just south of Washington, D.C. Locally
higher totals are possible across the central Apps of WV and VA,
where WPC probabilities for at least 8" mostly low (10-30%) outside
of the highest elevations.

Farther to the south, a transition zone is still expected where a
mixture of snow, sleet, and freezing rain will occur due to an
800-850mb warm nose aloft and a textbook winter CAD signature east
of the Apps in the surface pressure pattern that is forecast to
linger through Wednesday. This area of mixed ptype is most likely
from KY and into the Central Appalachians, especially along the
Blue Ridge of NC/VA. While some sleet is possible, the predominant
mixed p-type is likely to be freezing rain within this axis, and
will almost certainly be significant (to locally damaging) in the
vicinity of the Blue Ridge.

This first event winds down late Wednesday morning through the
afternoon /D2/, but just as the column begins to dry aloft, renewed
WAA ahead of the next system approaches within this progressive
pattern. While the DGZ dries out across the Mid-
Atlantic/Appalachians, the low levels re-saturate, and it is
possible in some areas there is never a break in wintry
precipitation due to very light snow/snow grains/freezing drizzle
Wednesday. Eventually the column re-saturates though as a more
intense low pressure developing over the Southern Plains lifts
northeast into the Ohio Valley with another round of mixed
precipitation spreading into the region.

This second wave will be stronger, but also farther inland, so
many areas will begin with snow or freezing rain and eventually
transition to all rain. The heaviest precipitation will likely
begin right around Wednesday evening in the Central Appalachians
and then expand northeast into the Mid-Atlantic. High pressure
wedging into the region will again force impressive isentropic
overrunning, and locations from northern VA through PA will likely
begin as a burst of moderate snowfall before quickly transitioning
to sleet, freezing rain, and eventually all rain before waning
Thursday evening. The heaviest snowfall is likely in the Poconos
and central PA terrain where WPC probabilities for 2+ inches are
as high as 50-70%, with icing exceeding 0.1" likely (>70%) in the
Laurel Highlands and parts of the Poconos.

WPC event total probabilities (12z/Tues to 12z Thurs) for more
than 0.25" are above 70% in the vicinity of the Blue Ridge where
locally more than 0.5" is also expected for some areas (50%
chance). There also exists some non-zero (5-15%) probabilities for
at least 1" of ice in terrain of far northwest NC and adjacent VA.
This will cause severe impacts including power outages, scattered
tree damage, and dangerous travel. Surrounding this, WPC
probabilities for more than 0.1" of 10-30% encompass a much larger
area including into parts of south- central VA and up the
Appalachians to near the MD Panhandle and Laurel Highlands.

...Central Rockies/Plains/Midwest/Great Lakes... Days 1-3...

Troughing over the northern Great Basin this evening will dip into
the central Rockies tonight, with broad WSW flow across CO. This
will favor an expansion of snowfall over the Medicine Bow mountains
and into the San Juans/Sangre de Cristos where upslope enhancement
will wring out several inches of snow area-wide. For the D1
period, WPC probabilities for at least 6 inches of snow are >50%
above 10,000ft or so.

By late tonight into early Wednesday, troughing will pass the
spine of the Rockies as low- level moisture increases over the
foothills to the Plains via SE to E flow. This will combine with NE
flow at the surface to increase snow into the Front Range, though
snow should generally be light overall. WPC probabilities for at
least 4 inches are near 20-30% over parts of the I-25 corridor.

The more intense snowfall will manifest farther east over Kansas
and southern Nebraska starting late tonight into Wednesday. There,
the potential exists for moderate to heavy snow across much of
Kansas as the upper jet extends from TX northeastward to the
Midwest. Combination of WAA, tightening thermal gradient
(increasing FGEN), and favorable/deep DGZ/isothermal layer will
promote locally heavy snow with >1"/hr rates (per WPC snowband
tool). A large high pressure to the north will supply NE winds to
the region but the gradient is not expected to be strong enough to
produce much blowing snow even as low pressure deepens over the
ArkLaTex. SLRs may eclipse 20:1 in the most favorable bands but
otherwise hover close to 15:1 along the I-70 corridor from GLD to
MCI. Further southeast across parts of central Oklahoma through
southeast Kansas and southern/central Missouri, overrunning will
favor sleet and freezing rain. WPC probabilities for at least 0.1"
ice are low- moderate in this region (10-50%) and highest over
Missouri. For snowfall, PVA and FGEN will force much of the
precipitation in advance of the trough with the axis of heavier
snowfall along I-70 toward/into Kansas City, then extending
northeastward. WPC probabilities for at least 4 inches of snow are
high (>80%) over most of central/northern KS into southern NE with
some probs (30-50%) for at least 8 inches.

By Wednesday night, the system begins to further organize and pick
up forward speed as a relatively weak surface low (>1000mb) lifts
through the Ohio and Tennessee valleys. The lack of rapid
deepening of the low pressure system due to the quickly lifting
longwave trough will prevent impacts associated with blowing and
drifting snow. Snow is expected to expand from southern IA and
northern/central MO through much of IL, southern WI, northern IN,
and the L.P. of Michigan. A narrow corridor of mixed ptype is also
forecast in a southwest to northeast band from southern MO through
central IN and northwestern OH. This narrow corridor of mixed ptype
could remain relatively stationary for a period of time across
Indiana and northwest Ohio for measurable freezing rain and sleet.
The combination of strong PVA and lower level FGEN into a deep DGZ
should provide for an axis of heavier snow, but where that
materializes is still bit fuzzy (including any lake enhancement
off Lake Michigan on NE winds) as some uncertainty in the 700 mb
fgen field and high SLR environment could prompt multiple areas of enhancement.

Right now, the highest probabilities of at least 6 inches of snow
maximize from northern MO through the Chicago metro and into
central Lower MI, with >60% probs extending to the NW and SE by
about 150 miles. This includes cities such as Kansas City, Chicago
and Milwaukee just to name a few. Within this region,
probabilities of at least 8 inches are moderate (>40%) from
northern MO to northern IL and across central Lower Michigan.

Like areas farther upstream (southern Plains), a mix or sleet and
freezing rain is likely closer to the track of the surface low due
to the overrunning of the cold surface with warmer air aloft over
portions of central IN into northwestern OH. There, WPC
probabilities of at least 0.10" icing have increased this forecast
cycle and are moderate (40-60%).

The positive-tilt to the pattern will help move the system along,
with precipitation ending Thursday morning over Michigan, though NW
flow on the backside will stir up some lake effect snow for U.P.
and L.P. of MI. Amounts should be light at the end of this forecast
period (12Z Thu - 12Z Fri).


.... Continued ...
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FOUS11 KWBC 130856
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Thu Feb 13 2025

Valid 12Z Wed Feb 12 2025 - 12Z Sat Feb 15 2025

...Great Lakes and Northeast...
Day 1...

Low pressure moving through the Ohio Valley this morning will
continue northeastward into southeastern Ontario, with broad WAA-
driven snow over northern New England D1 and an icy mix where
boundary layer sub-freezing temperatures persist beneath the
warming layer ~750-850mb (e.g., North Country, Green and White
Mountains). By this afternoon, a forming area of low pressure near
the Gulf of Maine will help maintain a colder column over much of
Maine, favoring more snow for the Pine Tree State via northerly
flow. After 00Z, the whole system will depart into Atlantic Canada.
WPC snowfall probs for >4" are highest (>50%) in the higher
elevations of the Adirondacks and Green/White Mountains, as well as
over the northern half of Maine. Freezing rain probs for >0.1" ice
are low (10-20%) over parts of central New England.

In its wake, NW/WNW/W flow across the mostly unfrozen Great Lakes
will support lake effect snow as 850mb temps of -15 to -20C move
across the region. WPC probabilities for >6" low (10-50%) over the
eastern U.P. of MI but are high (>70%) south of Buffalo with some
moisture flux through the ice and especially southeast off Lake
Ontario just north of SYR up to FZY. Snowfall totals locally over a
foot are possible.


...Sierra Nevada, Pacific Northwest through the Rockies...
Days 1-3...

...Atmospheric River with heavy Sierra Nevada snow affects
California tonight into Friday. Key Messages are linked below...

Upper low approaching 130W this morning is directing an
atmospheric river (AR) into NorCal then shifts south down the coast
to SoCal tonight as the low opens/splits into a slow-moving trough.

The atmospheric river has IVT around 500 kg/m/s (near the MAX in
the CFSR climo period) making for a wave of moderate to heavy
topographically- enhanced precip over the Sierra Nevada. Snow
levels around 6000-7000ft across CA this morning will drop back to
5000-6000ft under the trough axis tonight (Sierra) and around
4500ft (Shasta/Trinity). SLRs will be low to moderate given the
strong WAA, resulting in plenty of Sierra cement (>5ft and perhaps

8ft at the highest peaks). Snowfall rates will lessen into early

Friday (as SLRs rise a bit) and end completely by Friday night as
upper ridging builds in.

The lingering cold air brings light lowland snow and icing
potential for southern WA through western OR. Freezing rain threat
will advance northward on the edge of the precip shield this
morning from western OR (Coastal Ranges) northward across the
Columbia River into southwestern WA. WPC probs for >0.1" are
moderate (40-80%) for mainly the Coast Ranges west of the
Willamette Valley.

Moisture quickly spreads east throughout the Intermountain West
through Friday ahead of the slow-moving trough axis. Moisture
transport into the Great Basin and Wasatch/Rockies will be notable
per the ECMWF EFI and NAEFS IVT percentiles >99th percentile. WPC
probs for >8" are above 80% for the Tetons through the Wasatch and
Tushar Mtns (UT) and across the western slopes of the CO Rockies
with >60% probs for the Sawtooths of ID, and Kaibab Plateau in AZ
and northern NM ranges. Snow rates peak early Fri from west to east
as the trough axis drifts over the Rockies, but broad light to
locally moderate snow persists over much of the terrain into early
Sat (end of D2). By Sat/D3, the last piece of the broad longwave
trough will slip through the central Rockies, yield another several
inches of snow centered over western CO where WPC probs for at
least 6 inches are moderate (40-70%).

Finally, a sprawling North Pacific system will enter the PacNW at
the end of D3 with generally light snow for the WA Cascades.


...Upper Midwest/Great Lakes/Northeast...
Days 2-3...

Leading edge of the western trough Friday afternoon will manifest
itself at the poleward exit region of a 140kt upper jet across the
Plains and near the equatorward entrance region of the northern
stream jet across southern Ontario. This will promote broad lift
over the Upper Midwest with accompanying WAA atop an inverted
surface trough. Quick westward flow aloft will keep the system
moving through the region, but potential exists for a quick-hitting
few inches of snow with room for some localized bands of heavier
snow across WI. WPC probs for >4" snow are >50% over much of
central and southern WI to the IL border and into Lower MI.

Farther east into D3, snow will expand into the Northeast on
continued WAA ahead of a deepening upper trough and strengthening
upper jet arced from the Lower MS Valley to the St. Lawrence River
Valley. Light to moderate snow is forecast across southern Ontario
eastward into NY and New England where WPC probs for >4" snow are
moderate (40-70%), especially above 1500ft or so. Across the
interior Mid-Atlantic, cold surface temperatures from the departing
high pressure will be overrun with WAA precip, resulting in areas
of freezing rain from the southern Appalachians northward through
the Laurel Highlands into the Catskills. WPC probs for at least
0.1" icing are moderate (40-70%) with low-end (10-30%) probs for at
least 0.25" icing. This will depend on how strong the southerly
flow will be to scour out the cold surface temperatures vs precip
timing/onset and intensity.

Fracasso/Jackson

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

$$
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FOUS11 KWBC 140845
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
345 AM EST Fri Feb 14 2025

Valid 12Z Fri Feb 14 2025 - 12Z Mon Feb 17 2025

...Central NYS...
Day 1...

WNW flow will continue a lake effect snow band off Lake Ontario
into the Syracuse metro this morning/afternoon and diminish later
this evening as it lifts northward. Day 1 snow probs for >4" are
40-90% in a narrow corridor.

...Sierra Nevada through the Rockies...
Days 1-2...

Atmospheric River has moved well inland, but the lagging upper
trough will continue onshore flow with instability enhancing precip
over the Sierra Nevada as the low opens into a slow-moving trough.
Snow levels have fallen back to 5000-6000ft under the trough axis
(Sierra) and around 4500ft (Shasta/Trinity) bringing light snow to
lower elevations. Snow should taper off later this evening from
west to east across CA. Day 1 snow probs for an additional 8" are moderate(40-70%) across much of the Sierra.

Moisture has reached the Rockies with a strong influx from the SW
and the trough axis will pass the Four Corners early Sat, favoring
moderate to heavy mountain snow with gradually lowering snow levels
as colder air moves in. Snow rates will ease over the next 12-24
hours with additional snow over the Wasatch and Tushar in Utah and
western CO Rockies northward into the Tetons and eastward into the
San Juans and Sangre de Cristos. 48-hr snow probs for >12" are
over 80% for these areas.

...Pacific Northwest...
Days 2-3...

The next multi-vorticity lobe upper low in the northeast Pacific
will send a cold front into the Pac NW late Sat into early Sun.
Snow levels around 3000-4000ft for the northern-southern Cascades (respectively) will give light to moderate snow to the passes that
continue into early Monday as the trailing main upper low finally
reaches the coast. WSW flow will spread moisture across eastern OR
into ID, western MT and western WY where the favored terrain will
see moderate snow totals. Cold temperatures over the northern Great Basin/northern Rockies will favor at least some snow to most
valley floors. 48-hr snow probs for >12" are >50% for this higher terrain.

...Upper Midwest/Great Lakes/Northeast...
Days 1-3...

Eastward extension of the western trough will bring WSW flow to
the Upper Midwest later today with embedded vort maxes atop an
inverted surface trough. Thump of snow with this inverted trough is
on warm air advection, but sufficient cold air is there to allow
heavier snow with >10:1 SLRs over much of WI tonight. WPC snow
probs for >4" are >50% from southeastern MN across central WI. A
broader area of light snow is expected over much of the region,
setting up a somewhat prolonged but interrupted period of light snow.

Into D2, the western trough will push into the Plains and start to
amplify in concert with the downstream upper jet (>160kts) across
the Great Lakes. Moisture will continue to spread eastward across
Lower Michigan, southern Ontario, then into the Northeast. With a
trend toward a slower/sharper upper system, QPF has increased over
much of the Midwest and into Lower Michigan where WPC probs for at
least 4 inches of snow on Sat are >50% over most of Lower Michigan,
but are at least 25% from southern Iowa and across northern IL. On
the eastern side, WAA will promote light snow over much of NY with
WPC probs for >4" snow highest over the Poconos into the
Catskills, but also at least 30% over the higher elevations above
1500ft or so. To the south, cold air at the surface along/east of
the Appalachians (NC through VA into central PA) will hang tough as
overriding precip from the west encroaches, favoring freezing rain
and perhaps some sleet on Saturday. With a sfc low track from the
Mid-South through OH, warm air will eventually win out due to
strong 50kt SW 850 flow. WPC probs for at least 0.10" icing are

50% over southwestern VA northward into central PA, where there

are also probs for >0.25" icing (30-50%).

By D3, the surface low is forecast to track from just west of PIT
toward western/central NY with some coastal redevelopment over
southeastern MA (Cape Cod) that may move into the Gulf of Maine. A
lot of details have yet to be resolved, but this scenario will
likely result in all snow close to the Canadian border where warm
air intrusion is least likely, a mix of snow to sleet/freezing rain
over much of the area between the I-90 and I-80 corridors, and
rain farther south and southeast as warmer air surges up the coast.
The timing of the many players will modulate the amount of each
ptype, but for now the highest probabilities for at least 8 inches
of snow are over the Adirondacks into northern VT/NH and interior
Maine. Several inches of snow are probable (40-60% chance) along ad
north of the I-86/Rt 17 to I-84 corridor (NY to CT). Icing is most
likely in areas that are able to stay coldest the longest,
including central PA, the Poconos, Catskills, and Berkshires where
WPC probs for at least 0.10" icing are >50%. Again, the details of
the system are still in flux which will influence where and as what
type the precipitation may fall.

Fracasso

...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 150803
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
303 AM EST Sat Feb 15 2025

Valid 12Z Sat Feb 15 2025 - 12Z Tue Feb 18 2025

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

The upper trough centered across the Four Corners will continue
eastward today, with the last trailing vorticity pushing through
the CO Rockies this afternoon. Light to modest snow over the higher
peaks of CO into southeastern WY will diminsh through the day with
an additional 4-8+" likely and much lighter snow into the valleys
and Front Range.

...Corn Belt/Midwest/Great Lakes/Northeast... Days 1-3...

Trough in the Rockies will exit today with a long extension to the
northeast into the Upper Midwest. Base of the trough will lag
through TX but additional height falls out of Canada will slow the
northern stream, alloiwing the trough to recongeal as it heads into
the Ohio Valley and then the Northeast. The setup will be broad
WAA-driven snow into the Great Lakes and Northeast but as the
trough sharpens and jet becomes more S-shaped along 80W, low
pressure will deepen and surge mild air far northward toward the
Canadian border, allowing snow to change to sleet/freezing rain and
just rain through Sunday with the main low into western NY. By
that time, a new area of low pressure will start to take shape and
eventually take over southeast MA into the Gulf of Maine,
essentially halting the northward surge in milder air into/through
New England as the low finall then lifts northeastward along the
Maine coast and into Atlantic Canada by early Monday.

For D1, strengthening jet across Michigan into Canada will act to
maintain snowfall over Lower MI today where WPC probabilities for
at least 4 inches of snow are >50% for the central/eastern 2/3rds.
Into the Northeast, WAA-driven snow will overspread the region this morning/afternoon where temperatures are cold. Could capitalize on
good WAA for this front-end thump of snow but strong southerly
surge will drive the mixed ptype zone northward from the Mid-
Atlantic later this afternoon into tonight. WPC probs for at least
4 inches of snow are highest (>50%) farthest north where the cold
air will hang on the longest -- north of I-90 into the Adirondacks
and Green Mountains as well as into the Berkshires and Worcester
Hills. To the south, temperatures are sub-freezing thanks to high
pressure overhead this morning but aloft it is near and just above
0C. Any snow will turn to sleet or more likely freezing rain from
across the Midwest and especially into the central Appalachians (SW
VA into central PA then up into the Southern Tier of NY). Ice
accumulation will depend on how long the cold surface temperature
can resist the strong surge in mild air from the south. WPC probs
for at least 0.25" icing are at least 30% along the WV/VA line
northward to the I-99/US 220 corridor.

Into D2, low pressure over southeastern OH will track
northeastward toward western/central NY by the afternoon as the
coastal low takes shape, which should stop the northward push of
the mix ptype zone but not before it may reach all the way to the
Canadian border (NY/VT) and into Downeast Maine. The remaining cold
air will be largely confined to northern Maine where WPC probs for
at least 6 inches of snow are >50% north of I-95. Ice
accumulations will be primarily over eastern NY and north of I-95
into New England, especially into the Berkshires and Monadnocks
where ice probs for at least 0.25" are at least 20%.

By D3, storm will be well out into the Atlantic but with a broad
cyclonic flow back across the Great Lakes, supporting lake-effect
snow off all the lakes but especially off Lake Ontario on WNW flow.
This could support a healthy single band into the northern SYR
suburbs from Oswego toward Rome/Utica where at least several inches
of snow are possible.

...Pacific Northwest/Rockies/Central Plains... Days 1-3...

The next multi-vorticity lobe upper low in the northeast Pacific
will send a cold front into the Pac NW later today with snow levels
around 3000-4000ft for the WA/OR Cascades. With the upper jet
nosed into southern OR for the next two days or so, onshore flow
will continue to provide Pacific moisture to the region and into
the Great Basin/northern Rockies, overriding cold air on the east
side of the Divide. There, lower level convergence should enhance
snowfall over western MT D2 into D3 with two-day WPC snow
probabilities for >12" >70%. Snow into the Cascades will affect
the passes esp D1-2 until the trailing upper low finally reaches the coast.

Farther southeast, moisture will spread back into the central/CO
Rockies with additional amounts of at least 6 inches likely by D3.
Onto the Plains, incoming vort maxes in the quick WNW flow atop
lower-level WAA will favor light snow stretching from western NE
southeastward toward the MS River Valley including much of KS. The
air mass will be fairly cold thanks to high pressure starting to
assert itself across southern Canada into the Dakotas, supporting
SLRs ~15:1. Through 12Z Tue, WPC probabilities for at least 4
inches of snow are 40-60% over the northern half of KS into
southern NE with more to follow.

Fracasso

...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 160846
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
346 AM EST Sun Feb 16 2025

Valid 12Z Sun Feb 16 2025 - 12Z Wed Feb 19 2025

...Great Lakes/Northeast... Days 1-3...

A powerful multi-hazard winter storm will continue to push
into/through the Northeast today as the sharpening shortwave
beneath the 160kt jet exits the Midwest. Cold air over the
Northeast will eventually be scoured out nearly up to the Canadian
border as low pressure lifts from near PIT this morning to central
NYS this afternoon. By then, a new area of low pressure over Cape
Cod will start to become the dominant low and lift into the Gulf of
Maine as the old parent low weakens into western New England. The
new low will then move into Atlantic Canada tonight. The evolution
will favor all snow near the Canadian border and into interior
Maine where it will stay coldest thanks to the transfer of energy
to the coast, a transient mixed area of sleet/freezing rain to the
south, and rain surging northward after starting as snow this
morning farther south. Icing will hang on longer in the colder
terrain areas like the Adirondacks, Catskills, Berkshires/Greens,
and Worcester Hills/Monadnocks but also across coastal Maine on the
north side of the new area of low pressure. The low pressure
center will continue to deepen as it pulls away tonight into the
low 970s mb and the synoptic snow will end Monday morning.

WPC probabilities for at least 6 inches of snow today are highest
north of I-90 in NY, north of the MA/VT/NH border, and
north/northwest of I-95 through Maine. Totals near the Canadian
border and over northern Maine may eclipse a foot (probs 30-70%+).
Between the coast and I-90 or so, ice will be the main problem
before some areas change over, briefly, to a cold rain (esp the
valleys via strong southerly flow). WPC probabilities for at least
0.25" icing are highest (40-70%) in the Berkshires/southern Greens
and into the Worcester Hills/Monadnocks.

On the backside of the system, colder air will rush in across the
Great Lakes and into the central Appalachians, supporting lake
effect snow and upslope snow, respectively. Over eastern WV into
the MD Panhandle and the Laurel Highlands, upslope will provide for
modest snow totals with WPC probabilities of at least 4 inches

70%. Though that area will see snow ending on Monday, the lake

effect machine will keep cranking for the next few days as an upper
low swings through the region out of Canada. The flow will back
from NW to WNW and favor the typical lake belts, but especially
over the eastern U.P. of Michigan and southeast of Lake Ontario.
There, WPC probabilities for at least 8 inches of snow over the
next few days are high (>70%) and are moderate (40-70%) for 18
inches of snow in localized areas that remain under banding.

...Pacific Northwest/Rockies/Northern High Plains... Days 1-3...

An active Pacific jet will guide a lead system into the Northwest
today, followed by onshore flow into Monday, then another system by
Tuesday into Wednesday. Snow levels will be a bit below pass level
and waver there for the next couple of days. East of the Divide a
very cold air mass will be in place thanks to high pressure over
Canada that pushes southward through the Plains, setting up upslope
flow into western MT. For the first system, Sun-Mon (though into
Tue over WY), the highest snow totals will be over the Cascades
eastward into the central Idaho ranges, western MT/WY and into
northern CO/southern WY. Several feet of snow are likely in the
higher terrain with only a brief break between systems. IVT values
exceeding the 90th percentile will move through the region today,
but then drop after tonight as the jet flattens out a bit.
Nevertheless, the nearly continuous terrain-enhanced snow will
accumulate well over 1-2 ft with WPC probs > 70% in the mountains.
Snow will be fairly heavy over western-central MT on the upslope
side as well, where WPC probs for at least 8 inches of snow are

50% around Billings up to Great Falls.

The next system will enter the PacNW D3 (Tues afternoon) with some
light snow for the Cascades. This will push eastward into D4.

...Central Plains/Mid-MS Valley/Mid-South... Days 1-3...

Eastward extension of the Western US moisture will reach the
central Plains later this evening as WNW flow rushes through the
region. 700mb WAA will help drive light to modest snow across the
Black Hills southeastward into Nebraska overnight with fairly high
SLRs >15:1. Light snow will extend farther into northern MO by
early Monday before tapering off thereafter as the pattern shifts a
bit. WPC probabilities for at least 4 inches of snow D1-1.5 are
30-80% in this NW to SE stripe but diminish to <30% over northern MO.

Overnight Mon into Tue, height falls will dig through the Four
Corners with a multi-stream jet east of 100W. A strong Arctic front
will push southward and increase low-level convergence, helping to
drive an expansion of snow through KS and into northern OK and
eastward, growing heavier as the shortwave aloft reaches the Plains
Tues evening. Heavy snow is expected to develop over eastern KS
into western MO beneath a quickening upper jet east of the
Mississippi, bleeding southward into northern/northeastern OK and
northern AR overnight. By the end of the period, the shortwave will
continue into the Mid-South with light to moderate snow into TN.
On the southern side of the precip shield, colder air at the
surface will undercut the milder >0C thermals aloft over central AR
where freezing rain is likely to form (with some sleet to the north).

WPC probabilities for at least 4 inches of snow are >50% from
northwestern KS eastward to southern IL/western KY/northwestern TN,
including northern OK/AR. Within this broad region, an axis of
heavier snow is likely to develop with rates >1"/hr and snow totals

8". WPC probabilities for at least 8" are >50% over southeastern

KS and southern MO. Farther south, ice probs for at least 0.10" are

30% around the Ouachita Mountains.

Fracasso

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

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

$$
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FOUS11 KWBC 170823
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
323 AM EST Mon Feb 17 2025

Valid 12Z Mon Feb 17 2025 - 12Z Thu Feb 20 2025

...Great Lakes... Days 1-2...

Behind the exiting winter storm, cyclonic flow will remain over
the Great Lakes with 805mb temps < -20C. NW to WNW flow will favor
the typical MI belt regions but with an emphasis over the eastern
U.P. due to persistent light to moderate snow and especially
downwind of Lake Ontario. There, an intense single band may set up
today into Oswego and just north of Syracuse with some wavering N-S
into Tuesday. Two-day totals could exceed 18" (WPC probs > 50%)
with intense snowfall rates of 2-3"/hr. Strong pressure gradient in
place will keep winds elevated as well, creating blowing and
drifting of snow with especially hazardous whiteout conditions
within the band. Snow will gradually wind down into day 3.

...Pacific Northwest/Rockies/Northern High Plains... Days 1-2...

An active Pacific jet will maintain unsettled weather into the
Northwestern U.S. for the next 24 hours or so over the Cascades
into the northern Rockies. Height falls will continue moving inland
this morning with modest snows following along out of the Cascades
and into the Bitterroots/western MT this evening. East of the
Continental Divide a very cold air mass will be in place thanks to
high pressure over Canada that pushes southward through the Plains,
setting up upslope flow into western MT. Snow totals will be light
to modest in the higher elevations where WPC probabilities for at
least 8 inches of snow are >70%. Over central MT, light snow due
to upslope/easterly flow is expected from Billings to Kalispell but
WPC probabilities for an additional 4 inches are low (<40%) in the
lower elevations. As the height falls move into the Plains, snow
will gradually diminish on Tuesday.

Day 3...

The next system will enter the Pacific Northwest starting Tuesday
Night with some periods of snow for the Cascades, including into
the passes. Moisture plume will aim into Oregon but then move
quickly inland, helping to spread snow into the Northern Rockies
throughout the day on Wednesday (especially into the Blue Mountains
and into the central Idaho ranges). WPC probabilities for >6" of
snowfall are high (>70%) in these areas.

...Central Plains/Mid-MS Valley/Mid-South... Days 1-2...

The anomalous IVT responsible for periods of heavy snow in the
Rockies will accompany a period of 700mb WAA over the Central
Plains. The combination of 700mb FGEN and an accelerating 250mb jet
aloft will support a stripe of light/moderate snow from the Black
Hills southeastward through NE and into the Lower Missouri River
Valley today, weakening later today. Then tonight, the stronger
500mb shortwave trough tracking across the Central Rockies will
gradually deepen while upper-level diffluence increases at the nose
of a 250mb jet streak rounding the base of the Central Rockies
trough, setting up another area of snow from NW to SE. By early
Tuesday morning, KS will be within the entrance region of the upper
jet which will help promote an area of snow across central KS
where lower-level FGEN is maximized. Temperatures will be cold
behind an Arctic front, which should allow for SLRs ~15:1
especially in healthier bands. This area of snow will move
southeastward and increase in intensity into southeastern KS and
southern MO late Tue afternoon/evening where the 00Z CAM guidance
shows the potential for 1-1.5"/hr rates (per WPC snowband tool). By
early Wednesday the snow may diminish in intensity into KY as the
upper jet reorients itself and shifts focus to the Gulf coast,
setting up the coastal part of this event farther east. WPC
probabilities of at least 4 inches of snow are high (>70%) from
central KS eastward into MO and extreme southern IL. Within this
region, WPC probabilities for at least 8 inches of snow are
moderate (40-70%), especially over southern MO.

To the south of this swath of snow, cold surface temperatures
beneath >0C air aloft will promote an area of sleet and freezing
rain over central OK eastward into AR. A few hundredths of an inch
of icing is possible, especially into the Ouachita Mountains.

...Central/Southern Appalachians/Mid-Atlantic... Day 3...

The next phase of the system moving out of the Mid-MS Valley has
been in quite a bit of flux. Question revolves around the timing
and amount of interaction between the shortwave responsible for the
snow across KY/northern TN and the lead height falls ahead of the
upper low over the western Great Lakes/Corn Belt. A surface wave
should develop near the Gulf coast by early Wed and track eastward
then east-northeastward just off the Southeast coast to become the
new focus for QPF. Models have been wavering quite a bit on the
amount of development and how close to the coast this may be,
influencing how much QPF to surge into the southern Mid-Atlantic.
Overall trend continues to be a flatter and drier system and have
trended that way tonight.

Nevertheless, there is confidence in the wave development and at
least light to moderate QPF that will spread into the Southeast and
southern Mid-Atlantic from the system. The result will be a swath
of snow over southern and southeastern VA and northern NC with an
area of sleet and potentially significant freezing rain to the
south over eastern NC where QPF will be plentiful. WPC
probabilities for at least 4 inches of snow are >50% across southern/southeastern VA. Over NC, where the cold air in place
behind the departing system Sunday will be overrun with >0C air
aloft, the icing potential is significant. WPC probabilities for at
least 0.25" ice are at least 30% but may rise in future updates.

Fracasso

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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

$$
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FOUS11 KWBC 180811
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
311 AM EST Tue Feb 18 2025

Valid 12Z Tue Feb 18 2025 - 12Z Fri Feb 21 2025


...Great Lakes...
Days 1-3...

Cyclonic flow over southern Canada and the Great Lakes on the
western side of the elongated upper trough axis will favor a
continuation of the lake effect snow for the next couple of days.
With 850 temperatures in the -20sC and NW to WNW flow, multi-bands
will form off the Upper Lakes with a strong single band off Lake
Ontario with an impressive multi-lake moisture feed. THe pattern
will be slow to unfold, but by early Wednesday a closed low will
begin to form over the Corn Belt which will help disrupt the
pattern enough to diminish the lake effect snow, but then those
height falls will bring in a general/light snow to the region on
Thursday. WPC probabilities for at least 8 inches of snow over the
next two days are near 50% over the eastern U.P. of Michigan. Over
central NY between ROC-FZY-SYR, the strong single band will
continue to dump snow at 1-3"/hr rates with significant
accumulation in a narrow swath -- perhaps more than 12-18 inches

60% probs). By day 3, snowfall will be light with most areas

seeing less than 4 inches of snow.


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

Height falls over the Great Basin this morning will continue
southeastward today, giving some additional snow to the CO Rockies.
To the north, additional height falls out of Canada will drop
through central MT with some light snow to the central ID ranges,
southwestern MY, and the western WY ranges where WPC probabilities
for at least 6 inches of snow are low (<40%) to the north but high

70%) over western WY and the high peaks of the northern CO Rockies.

By day 2, a Pacific system will start to move into the Northwest,
spanning the latitudes from NorCal up to the Canadian border. IVT
will be modestly high (~90th percentile) into NorCal/southern
OR/northern NV toward Idaho, supporting light to moderate snows for
the terrain with snow levels near 3000ft to the north and 5000ft
to the south that will rise a bit as the core of the moisture plume
pushes through. The system will move steadily along and clear the
coast with QPF starting early Thursday, pushing into northern
UT/southern ID and into the Rockies. However, moisture will wane
and snow will become lighter overall into D3 with the snow confined
mainly to the Unitas and higher CO Rockies by then. For the 3-day
period, WPC probabilities for at least 8 inches of snow are highest

70%) over the higher terrain above 6000ft closer to the coast,

7000-8000ft over the Great Basin, and 9000ft over CO/WY.


...Central Plains through the Mid-Atlantic States...
Days 1-2...

A significant winter storm is underway over the Central Plains
which will spread eastward through the Mid-South into the southern
Mid-Atlantic with potentially major impacts including heavy snow
and significant ice.

Snow is already underway across KS into MO this morning, driven by
lead shortwaves ahead of the Rockies trough. Through this morning,
as the stronger height falls approach the region, snow will expand
over the central and southern Plains eastward beneath the RRQ of
the upper jet and atop the Arctic air mass driven in by the strong
cold front overnight. With sufficient moisture influx from the
Gulf, snow rates will increase over southern KS into southern MS
later this morning into the afternoon with >1"/hr rates at times
per the WPC snowband tool and HREF probs. Snow will advance
eastward into the Mid-South later this evening and overnight but
likely diminish somewhat in intensity. To the south, the shallow
Arctic air mass will continue southward but southerly flow aloft
will maintain >0C temperatures, favoring a mix of sleet and
freezing rain over parts of OK into AR, northern LA, and western
MS. For the D1 period, WPC probabilities of at least 4 inches of
snow are high (>70%) from southeastern KS and northeastern OK
eastward to western KY. Within this region, probabilities of at
least 8 inches of snow are >60% near Joplin to Springfield, MO.
Icing to the south should generally be light but there is a low
change (10-30%) of at least 0.10" accretion near the Oachita
Mountains in AR.

By Wednesday morning, the next phase of the system will take shape
over the northern Gulf as the entrance region of the upper jet
touches the LA/MS coast, helping to favor cyclogenesis. The
northern part of the system will still spread snow across the Mid-
South eastward to the central Appalachians where some orographic
lift will help wring out several inches of snow into eastern
KY/southern WV/southwestern VA. The larger QPF-maker will be the
forming Gulf low that is forecast to track ENE to NE across north
FL before turning northeastward along the Gulf Stream just off the
SC/NC coasts. With the cold air mass in place through the East,
this sets up a southern slider snow event with an axis of heavy
snow along the VA/NC border into the Tidewater and southern
DelMarVa. The incoming northern stream upper low will lag behind
just enough to not phase until farther downstream, but enough
ingredients will be coming into place in the formative stages of
this system to yield a modest to heavy snowfall for parts of the
southern Mid-Atlantic, with a cutoff near a line along I-66/I-95
into southern NJ. WPC probabilities for at least 6 inches of snow
are highest over southeastern VA and northeastern NC, squarely
through the Norfolk area.

Like places farther west, the >0C air aloft will rise up and over
the cold surface temperatures over eastern NC, setting up a
freezing rain event that may be significant along and east of I-95
between the VA border and into northeastern SC. There, WPC
probabilities for at least 0.10" icing are >50% with some areas
receiving more than 0.25" accretion.


...Southeastern Mass...
Day 3...

The exiting system from the Southeast/southern Mid-Atlantic will
track northeastward, and may clip southeastern MA/Cape Cod D3 on
its way into Atlantic Canada. The question revolves around the
speed of the incoming northern stream upper low and how much it can
capture the exiting system. Given the uncertainty leading into the
event in the Southeast/Mid-Atlantic, there are still a wide range
of solutions from zero to moderate snow over part of the region.
For now, there are low (10-40%) probabilities of at least 4 inches
of snow over Cape Cod and the Islands.


Fracasso


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

https://www.wpc.ncep.noaa.gov/key_messages/LatestKeyMessage_2.png

$$
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