FOUS11 KWBC 030740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Thu Apr 3 2025

Valid 12Z Thu Apr 03 2025 - 12Z Sun Apr 06 2025


...Northeast...
Days 1 & 3...

An icy wintry mix will continue from the White Mountains and
through much of interior Maine this morning as ongoing WAA and
intense 850mb FGEN sustains an icy setup over northern New England.
The lingering sub-freezing boundary layer will gradually erode as
the warm front advances northward with only northern Maine holding
on to any notable wintry mix through midday. WPC probabilities
depict low chances (10-30%) for additional ice accumulations >0.1"
in the White Mountains and western Maine through this morning.

Following a break in the action Thursday night through Saturday
morning, the next round of wintry mix arrives Saturday afternoon
as moisture from the Mississippi Valley streams northward into New
England. Similar to the Day 1 setup, low-mid level WAA and 850mb
FGEN are the primary mechanisms of lift that will promote
precipitation. The antecedent air-mass is not nearly as cold as the
Wed-Thurs air-mass. However, the modestly cold air-mass will be
tough to erode in the higher terrain, thus making the White
Mountains and western Maine the most likely areas to see a mix of
snow and freezing rain through Saturday night. WPC probabilities
show moderate- to- high chances (50-70%) for >0.1" of ice, with low
chances (10-30%) for ice accumulations >0.25".


...Intermountain West & Southern High Plains...
Days 1-3...

The weather pattern over the western third of the Lower 48 is
primarily driven by a pair of upper level disturbances; one
tracking across Montana today and early Friday, and the other is a
closed upper low over the Southwest. Starting in Montana, a cold
front at the leading edge of the 500mb shortwave trough will act as
a trigger for snow showers, some of which could have snow squall-
like impacts with bursts of snow and gusty winds Thursday
afternoon. With high pressure building in from Alberta, easterly
upslope flow into the Lewis Range and Absaroka through Thursday
evening. Snow associated with this upper trough is also expected as
far south as the Big Horns and even as far east as western North
Dakota Thursday night. By Friday morning, the cold front makes its
way south through the Central Plains and Central Rockies with
NErly upslope flow aiding in minor snow accumulations along the
Front Range of the WY/CO Rockies through Friday morning.

Farther south, the closed upper low will make its way toward New
Mexico with 200-500-700mb heights along the AZ/NM and Mexico
borders below the 10th climatological percentile. As the 700mb low
reaches western New Mexico Friday afternoon, winds over southeast
CO and northeast NM will turn easterly at the same time the
aforementioned cold front to the north plunges south. Southern CO
and northern NM will also be co-located beneath the divergent left-
exit region of a 500mb jet streak located over northern Mexico. The
heaviest snowfall looks to ensue Friday afternoon and into Friday
night across the Front Range, Palmer Divide, San Juans, and Sangre
De Cristo (including Raton Pass). By Saturday morning, snow is
forecast for most of the Southern Rockies and even parts of the
southern High Plains as the cold front continues to dive south and
the deformation zone on the northern and western periphery of the
700mb low moves in overhead. Note that with the time of year, it
will have to snow exceptionally hard (>1"/hr) for snow to
accumulate outside of the mountain ranges given the higher sun
angle and warmer soil temperatures. Still, periods of moderate snow
combined with 30-40 kt 850mb winds will cause poor visibilities
through Saturday afternoon before the snow finally tapers off
Saturday evenings.

WPC probabilities depict moderate-to-high chances (50-70%) for
snowfall >8" along the >9,000ft peaks of the Sangre De Cristo and
San Juans between Friday afternoon and Saturday afternoon. Along
the I-25 corridor, the most concerning area for heavy snowfall is
along Raton Pass where up to 12" of snow in the forecast. WSSI
depicts Moderate impact potential in the Sangre De Cristo, Raton
Mesa, and San Juans. Note that there are some Moderate Impacts in
the plains of eastern NM and the TX Panhandle with Blowing Snow the
primary impact in these areas.


Mullinax


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FOUS11 KWBC 031909
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
309 PM EDT Thu Apr 3 2025

Valid 00Z Fri Apr 04 2025 - 00Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1,2...

A deep upper level trough over much of the Intermountain West and
associated embedded upper level low over the Southwest will
gradually shift east onto the Plains through Saturday. Shortwave
disturbances moving around both the upper low and a secondary wave
moving along the Canadian border will provide the forcing for
wintry weather over and immediately downwind of those upper level
features.

For Day 1/Tonight through Friday, a potent trough over the Canadian
Prairies will dig southeastward into Montana and the Dakotas. This
will lead to pressure and height falls in the region. Troughing
developing as a response will draw a small portion of the Gulf
moisture plume into the northern Plains, supporting a widespread
generally light snowfall over Montana and the Dakotas. For the
mountains from the Bitterroots of Montana south to the Front Range
of Colorado, localized upslope along the terrain will cause much
heavier snowfall rates and amounts, especially in the Beartooths of
Montana and Bighorns of Wyoming, where new snowfall could approach
a foot through midday Friday. WPC probabilities are over 50% for 4
inches or more of snow for the Front Range of Colorado and the
Beartooths of Montana and Wyoming.

For Day 2/Friday Night and Saturday, the shortwave moving along the
Canadian border will shift east into the Great Lakes, leaving the
area. However, the upper level low/southern extension of the
broader upper trough will begin to tap ever-increasing amounts of
Gulf moisture as the lift ahead of the low moves in closer
proximity to the trough. This will draw more of that moisture
westward into the southern High Plains as the low-level jet
increases in both strength and amounts of Gulf moisture it will be
drawing northward into the nation's mid-section. Upslope will play
an even greater role here, especially as the leeside surface trough
develops over eastern New Mexico. Some of the troughing from the
northern system from Day 1 in the northern Plains will propagate
straight southward along the Front Range and support the heavy
snow. The Sangre de Cristo Mountains of Colorado and New Mexico
will be the range hardest hit with heavy snow, with WPC
probabilities for over 8 inches of snow in the moderate-to-high
(50-70%) range through Saturday evening. The WPC Winter Storm
Severity Index (WSSI) shows areas along the state line near Raton
Mesa with major impacts from the large snowfall expected. The snow
will taper off in the area Saturday night.

...Northern New England...
Day 3...

A strong upper level trough over Hudson Bay Saturday will direct a
strong shortwave along its southeastern periphery towards New
England. Meanwhile, a portion of the moisture associated with the
excessive rainfall over the nation's mid-section will draw
northeastward into the Northeast and New England. Here, that Gulf
moisture will interact with some lingering cold air over the
region, resulting in a variety of precipitation types over the
area. For areas south and west over northern New Hampshire and far
western Maine, a significant icing event is expected as warmer air
above freezing moves in aloft above the cold air in place,
resulting in precipitation changing over from snow to sleet and
freezing rain as the warm air moves in and deepens Saturday night.
There is a moderate-to-high (50-70%) chance of at least a tenth
(0.10") of an inch of ice across much of northern New Hampshire and
far western Maine near the New Hampshire border through Saturday
night, with a low (10-30%) chance of at least a quarter of an inch
of ice.

Further north where the warmer/above freezing air is unable to
reach, a light snowfall is expected, namely for far northern Maine,
where there is a low-to-moderate (30-50%) chance of at least an
inch of snow Saturday night. The moisture plume will shift east
with the cold front Sunday morning, ending the winter precipitation
threat.

Wegman

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FOUS11 KWBC 040735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Fri Apr 4 2025

Valid 12Z Fri Apr 04 2025 - 12Z Mon Apr 07 2025

...Portions of the Rockies and the High Plains...
Days 1-2...

This morning, a cold front tracking south through the central High
Plains with NErly CAA will cause temperatures to drop and modest
upslope ascent into the Front Range of the Rockies. This air-mass
will be essential for boundary layer wet-bulb temperatures being
cold enough to support snow in the central and southern High
Plains. Farther south, a closed upper low will slowly make its way
east through Arizona and New Mexico on Friday while also injecting
a healthy plume of 300-700mb moisture over the Rockies. This will
support periods of mountain snow from as far west as the Wasatch
and as far south as the Gila Mountains of eastern Arizona. As the
700mb low heads into western New Mexico Friday afternoon, low-mid
levels winds over southeast CO and northeast NM will turn easterly
at the same time as the aforementioned cold front to the north
continues its southerly progression. In addition, the southern and
central Rockies/High Plains will reside beneath the divergent left-
exit region of a 500mb jet streak. Guidance shows a moistening of
the 700-300mb layer Friday afternoon that coincides with what is
likely to be the start of heavy snowfall from the San Juans and
Front Range on south along the Sangre De Cristo and Raton Mesa
Friday afternoon and into Friday night.

By Saturday morning, snow will be falling not only in the Southern
Rockies, but across the southern High Plains thanks to a narrow
area of 700mb WAA to the north of the 700mb low tracking from
southeast NM into western TX. This will prompt the formation of a
deformation zone on the western and northern flanks of the 700mb
low. Note that, with the calendar reading early April and the
increasingly high sun angle, it will have to snow at an
exceptional clip (>1"/hr)for snow to accumulate outside of the
mountain ranges. Still, periods of moderate snow combined with
30-40 kt 850mb winds will cause significantly reduced visibilities
across the southern High Plains of eastern NM and the OK/TX
Panhandles through Saturday afternoon. Snow should finally taper
off by Saturday evening as the 700mb low tracks east over central OK.

The ECMWF EFI does suggest this is a rather anomalous event in
terms of snowfall for the late March to mid-April time period. The
EFI shows a large swath of 0.8-0.9 values from Raton Pass on south
through much of eastern New Mexico. WPC probabilities show high
chances (>70%) for snowfall totals >12" along the >9,000ft peaks of
the Sangre De Cristo and above 8,000ft in the Raton Mesa. The
latest forecast calls for as much as 12" of snow at the peak of
the Raton Pass along I-25. The WSSI does indicate Major Impact
potential (considerable disruptions; dangerous to impossible
travel) along the Raton Pass Friday night into Saturday morning.
WPC probabilities also show moderate-to-high chances (50-70%) for
snowfall >4" along the I-40 corridor in eastern NM. The WSSI shows
Minor to Moderate Impacts from a combination of Snow Amount and
Blowing Snow across the High Plains of eastern NM and the OK/TX
Panhandles through Saturday with Minor Impacts denoted (winter
weather conditions, hazardous travel possible) in and around the
Amarillo area.


...Northern New England...
Day 2...

Saturday will bring yet another round of wintry weather from the
White Mountains through much of western and northern Maine. While
the air-mass is not as cold as the more recent winter storm that
took place earlier this week, high pressure over Quebec will
provide a weak source of sub-freezing boundary layer temps. As
850-700mb WAA and 300K isentropic ascent amidst brisk SWrly flow
aloft increases, a ribbon of 850-700mb areal-averaged FGEN will
support a band of moderate-to-heavy precipitation that runs
directly over the marginally cold air-mass in northern New England
on Saturday. Precipitation may briefly start out as snow (staying
all snow longest over northern Maine), but the burgeoning nose of

0C temps at low-levels will inevitably switch any snow to a

sleet/freezing rain mixture from the Whites to western Maine
Saturday afternoon. A weak CAD signature will linger longest along
the Maine/Quebec border that will linger through Saturday night. By
Sunday morning, the warm front lifts far enough north to have plain
rain be the primary precipitation type.

WPC probabilities show moderate-to-high chances (50-70%) for ice
accumulations >0.1" from the Whites through western Maine. Some
minor ice accumulations (generally <0.1") are possible in the Green
Mountains and even as far south as the Berkshires. However, if any
locations are to see localized ice accumulations >0.25", it would
be the White Mountains and western Maine where low-to-moderate
probabilities (10-40%) are present. The probabilistic WSSI (WSSI-P)
does indicate moderate-to-high chances (50-70%) for Minor Impacts
as a result of the >0.1" of ice accumulations.

...Northern Great Lakes...
Day 3...

A potent 500mb vort max with origins out of the Arctic Circle will
dive south from south-central Canada towards northern Minnesota
Sunday evening. A 250mb jet streak oriented N-S will place its
divergent left-exit region over the Midwest Sunday night and aid in
the development of low pressure along a strengthening 850mb front.
A narrow band of moderate snow should manifest on the northern
periphery of low pressure as it tracks through Wisconsin and
northern Michigan. In addition to the band of snow, CAA via brisk
northerly winds will trigger lake-enhanced snow showers over
northern Wisconsin and the Michigan U.P. Sunday night and Monday
morning. WPC probabilities highlight low chances (10-30%) for >4"
of snowfall through 12Z Monday in the Michigan U.P. and the tip of
Michigan's Mitten with additional snowfall possible across northern
Michigan through Monday afternoon.


Mullinax

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FOUS11 KWBC 050732
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
332 AM EDT Sat Apr 5 2025

Valid 12Z Sat Apr 05 2025 - 12Z Tue Apr 08 2025

...Southern Rockies and the Southern High Plains...
Day 1...

A 700mb low tracking across southern New Mexico this morning has
all the necessary ingredients at its disposal for a classic April
winter storm in the southern Rockies and High Plains. Modest
700-300mb moisture aloft will overrun an air-mass that is becoming
increasingly colder through two methods: CAA in wake of the cold
frontal passage, and the other being dynamic cooling aloft within
the developing deformation axis. The mountain ranges of the
southern Rockies (Sangre De Cristo, southern Front Range, San
Juans, Sacramentos) will see the heaviest snowfall rates which can
surpass 2"/hr in some cases through this morning. As the 700mb low
emerges over eastern New Mexico, periods of heavy snow and gusty
winds will produce hazardous travel conditions across the High
Plains of eastern New Mexico, southeast Colorado, and the Texas
Panhandle through Saturday evening. There could be instances of

1"/hr snowfall rates over eastern New Mexico and the Texas

Panhandle during the day. Snow should taper off across West Texas
Saturday night, while a brief burst of snow over central Oklahoma
could produce a swath of light snow as far east as southwest
Missouri.

WPC snowfall probabilities show moderate-to-high chances (50-80%)
for >8" in terrain from the Raton Mesa on south along the Sangre De
Cristo and all the way to the Sacramentos which have 50-70%
chances for >12". Much of east-central New Mexico along I-40 shows moderate-to-high chances (40-70%) for snowfall totals >4"with low-
to-moderate chances (20-50%) in portions of the Texas Panhandle
between Amarillo and Lubbock. The WSSI shows a large footprint of
Moderate Impacts from the Southern Rockies and eastern New Mexico
to the Texas Panhandle with the Snow Amount and Blowing Snow impact
criteria being the primary drivers in the WSSI algorithm. Expect
hazardous travel conditions in these area today and into parts of
tonight.


...Northern New England...
Day 1...

Today, another round of wintry weather arrives from the White
Mountains of New Hampshire through western Maine that will continue
through Saturday night. The airmass is not as cold as the more
recent winter storm that took place earlier in the week, but high
pressure over Quebec will anchor a weak source of sub-freezing
boundary layer temps. As 850-700mb WAA and 300K isentropic ascent
amidst brisk SWrly flow aloft increases, a ribbon of 850-700mb
areal-averaged FGEN will support a band of moderate-to-heavy
precipitation that runs over the marginally cold air-mass in
northern New England on Saturday. Precipitation may briefly start
out as snow (staying all snow longest over northern Maine), but the
burgeoning nose of >0C temps at low-levels will inevitably switch
any snow to a sleet/freezing rain mixture from the Whites to
western Maine Saturday afternoon. A weak CAD signature will linger
longest along the Maine/Quebec border through Saturday night. By
Sunday morning, the warm front lifts far enough north to have plain
rain be the primary precipitation type.

WPC probabilities show moderate-to-high chances (50-80%) for ice
accumulations >0.1" from the Whites through western Maine with up
to 40% probs for >0.25" in the Presidential Range of the Whites.
The WSSI is depicting moderate impacts from this icing event within
the hardest hit areas of the Whites and western Maine.


...Michigan...
Days 2-3...

A vigorous 500mb vorticity maximum originating out of the Arctic
Circle several days ago will track south from southern Canada
towards Minnesota Sunday night. A 250mb jet streak oriented N-S
will place its divergent left-exit region over the Midwest Sunday
night and aid in the development of low pressure along a
strengthening 850mb front. A narrow band of moderate-to-heavy snow
will manifest itself on the northern periphery of the developing
storm system as it tracks across Michigan's Mitten early Monday
morning. In addition to the primary band of snow, CAA via brisk
northerly winds will trigger lake-enhanced snow showers over
Michigan's U.P. and the northern-most portions of Michigan's
Mitten through Monday afternoon. Snow should finally taper off by
Monday evening as the storm races east. WPC probabilities show
low-to-moderate chances (20-50%) for snowfall accumulations >4" in
northern Michigan through Monday evening.

The wave of low pressure will continue its eastward progression
across the Great Lakes Monday afternoon and along the Northeast
U.S./southeast Canada border Monday night. Periods of light snow
are possible from the eastern Great Lakes to the northern
Appalachians Monday night and into Tuesday morning. Light
accumulations between a coating to as much as 2" are possible with
the highest elevations of the northern Appalachians having the best
odds of seeing the higher end of those snowfall accumulations.


Mullinax


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FOUS11 KWBC 060735
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
335 AM EDT Sun Apr 6 2025

Valid 12Z Sun Apr 06 2025 - 12Z Wed Apr 09 2025


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

A potent 500mb vorticity maximum tracking south from southern
Canada will provide modest upper level ascent when working in
tandem with a N-S oriented 250mb jet streak over the Great Lakes
Sunday evening. At lower levels, low pressure will develop beneath
the favorable diffluence and along a strengthening 850mb front. A
narrow band of moderate-to-heavy snow will ensue on the northern
periphery of the developing storm system as it tracks across
Michigan's Mitten late Sunday night and Monday morning. In addition
to the primary band of snow, CAA via brisk northerly winds will
trigger lake-enhanced snow showers over Michigan's U.P. and the
northern tier of Michigan's Mitten through Monday afternoon. As
daytime heating lessens late in the day, snow shower coverage
should diminish with only an unusually cold air-mass filtering in
behind the departing storm system. WPC probabilities show low-to-
moderate chances (30-50%) for snowfall totals >6" across the
northern-most portions of Michigan's Mitten. Similar probabilities
are present across much of the eastern Michigan U.P. for snowfall

6" through Monday evening.

...Interior Northeast...
Days 2-3...

Following a minor snowfall accumulations from northern Pennsylvania
on east through the northern Appalachians Sunday night, the
primary low responsible for the snow over Michigan makes its way
east through southern Ontario Monday afternoon. A strong cold front accompanying the storm system will escort rain showers along and
ahead of the front, but a dramatic temperature drop behind the
front will lead to a changeover to snow starting Monday afternoon
across the Lower Great Lakes, then over the northern Mid-Atlantic
Monday evening. It is still early to determine if there is a
notable snow squall threat, but the quick changeover from rain to
snow could cause a rapid reduction in visibilities for affected
areas.

By Monday night, the aforementioned 500mb vorticity maximum in the
"Northern Great Lakes" section will continue to foster exceptional
PVA ahead of the trough. The storm system will continue to
strengthen as it tracks across the St. Lawrence River Valley early
Tuesday morning and across northern New England later in the day
Tuesday. There is a compact TROWAL on the back side of the storm
that will foster a narrow deformation zone on the backside of the
storm. In addition, CAA on the backside will provide some lake-
enhanced snow Tuesday morning and into Tuesday afternoon. The storm
will race east over the eastern Canadian Maritimes Tuesday night
and snow will quickly taper off. WPC probabilities show an
expansive area of low-to-moderate chances (30-50%) for snowfall
totals >4" from the Tug Hill on east across the Green/White
Mountains and northern Maine. These locations also sport low chance probabilities (10-30%) for localized snowfall amounts >6" through
Tuesday evening.

WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are below 10%.


Mullinax




$$
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FOUS11 KWBC 072007
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
407 PM EDT Mon Apr 7 2025

Valid 00Z Tue Apr 08 2025 - 00Z Fri Apr 11 2025

...Interior Northeast...
Days 1,2...

A compact low tracking from Lake Huron this afternoon east along
the Canadian border and across Maine through Tuesday afternoon will
cause an area of mostly light snow to fall along its track, as most
locations near the track stay below freezing, favoring mostly snow
as the precipitation type. The initial front is largely over the
Ontario Peninsula (the area bounded between Lakes Huron, Erie, and
Ontario) at the time of this writing. Temperatures with this band
are largely above freezing, so any snow embedded within it is not
sticking, especially to roads. Going into tonight, however, without
solar insulation, it's likely on the higher elevations of the
Chautauqua Ridge, and eventually Adirondacks and points further
east, snow will begin sticking and have some impacts.

The greatest impact from this low for most areas is likely to be
the potential for flash freezing. As sub-freezing air moves in with
the snow, road/ground temperatures could rapidly drop, resulting in
a thin glaze of ice on some colder surfaces. This of course may
have travel impacts. With the snow itself, in some of the stronger
convective cells, visibility in any snow may drop enough to cause
travel impacts as the winds with the snow and cold front become
gusty. Fortunately, the snow is not expected to become very strong,
as a stronger low along the moisture plume off the Eastern Seaboard
saps a lot of energy from this polar low as they track parallel to
one another.

As far as snow amounts are concerned, impacts from this low will
start tonight, increase through the day Tuesday, then peak Tuesday
evening as the snow rates wane as the parent low moves off to the
east. A few inches of accumulation are possible in the valleys from
the Champlain Valley east to coastal Maine. Meanwhile, locally
much greater impacts from much higher accumulations are expected
from the Tug Hill Plateau of central New York to the west, to the
Adirondacks, the northern Greens and Whites of VT and NH,
respectively, and much of western Maine. Local accumulations on the
highest elevations could approach a foot of new snow by the time
the snow is all said and done.

WPC Probabilities are moderate-to-high (50-70%) across far northern
New Hampshire and much of western Maine for 6 inches or more of
snow. Since the heaviest snow will be falling during the day
further west across northern New York and Vermont, those
percentages are much lower (10-30%) in those mountains. Minor
impacts are expected in these areas, though where snow falls
heavier in any convective snow showers, locally greater impacts are
probable.

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

Extensive lake-effect snow is expected behind the aforementioned
low that is moving through the Great Lakes currently. 850 mb temps
will be falling to the west (cold side) of the low to between -12C
and -18C across all of the Great Lakes tonight. Despite this being
the climatologically unfavored time of year for lake-effect (due to
usual warm air in place over the cold lakes), the air will be cold
enough in this case for all of the lakes to support multiple bands
and cellular lake-effect convection from the U.P. of Michigan,
where lake-effect snow is ongoing presently, to western Michigan
off its namesake lake, and later tonight off the lower lakes
through the Chautauqua Ridge and Tug Hill Plateau. As usual with
lake-effect, the typical impacts such as rapidly reduced
visibilities, snow-covered roads, and blowing snow are likely in
the aforementioned impacted areas. The heaviest lake-effect and
greatest snowfall amounts are expected on the Tug Hill where
amounts approaching 10 inches are possible through Tuesday.

A developing low along a slow-moving warm front extending from the
Arrowhead of Minnesota through southern lower Michigan and
eventually into portions of northern New York may cause additional
areas of snow Wednesday Night into Thursday morning. As is typical
during April, temperatures will be hovering right around freezing,
so precipitation type between snow and rain will be a major
determining factor as to accumulations in any one area. A general
1-3 inches of snow are possible in these areas from the low and
front.


...Northern Rockies and Cascades...
Days 1,2...

A pair of shortwave troughs rotating east along the base of a
longwave trough over the northeast Pacific will direct plumes of
Pacific moisture into the Pacific Northwest through Wednesday. Snow
is expected to remain at higher elevations, especially over the
Olympics and Cascades. Higher elevations such as Mt. Rainier may
see multiple feet of snow through the period due to very persistent
and heavy upslope snow. Accumulations will be extremely elevation
dependent, as many valley locations see mostly rain or snow light
enough to not be able to stick to warm surfaces. Measurable snow
will impact many of the mountain ranges of the Pacific Northwest,
including the Blue, Sawtooth, Bitterroots, Absaroka, Teton, and
Lewis Ranges. Strong ridging building in behind the troughs by
Wednesday and Wednesday night will end any remaining high elevation
snow.


Wegman

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FOUS11 KWBC 090740
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
340 AM EDT Wed Apr 9 2025

Valid 12Z Wed Apr 09 2025 - 12Z Sat Apr 12 2025

...Great Lakes & Interior Northeast...
Days 1-2...

A fast approaching upper-level trough producing modest PVA aloft
at the same time as the diffluent left-exit region of a 120kt jet
streak moves in over the Great Lakes Wednesday afternoon and
through Wednesday night. As a wave of low pressure tracks east
along a strenghtening low-level warm front, a swath of
precipitation along the warm front and on the northern flank of the
storm will be capable of producing periods of snow. The setup
continues to feature very marginal boundary layer temperatures,
making it essential for dynamic cooling and the transition to snow
after sunset Wednesday evening to help snow accumulate. The wide
ranging solutions in guidance include little to no snow or as much
as several inches from southern Wisconsin on east to southern
Michigan and both northern Indiana and Ohio (showcasing the
complexities of the setup detailed above). WPC probabilities show
low chances (10-30%) for snowfall totals >2" across southern
Michigan, while most areas in the Lower Great Lakes see a coating
to 2" throughout the Lower Great Lakes.

A similar setup for light snow occurs over the Northeast mountains
Wednesday night into Thursday. Mountain ranges such as the
Catskills, Adirondacks, and Berkshires could see between a coating
to 2" of snowfall through Thursday night. A break in the snow
arrives Friday morning before another round of mountain snow
arrives late Friday into Saturday.


...Northern & Central Appalachians...
Day 3...

As the upper-level trough over the Ohio Valley deepens Thursday
night, excellent upper-level divergence via PVA ahead of an
embedded shortave disturbance will spawn a strengthening area of
low pressure in the Mid-Atlantic. Out ahead of the upper trough is
an IVT >400 kg/m/s that will deliver copious amounts of moisture
into the northern Mid-Atlantic and Northeast Friday and into
Saturday. While there is some residual sub-freezing air in the
Northeast, there is only enough to support snow in the more
elevated terrain of the central and northern Appalachians.
Elevations above 2,000ft are most favored for snowfall, but some
areas as low as 1,000ft in elevations could see rain transition to
snow Friday night. This is a sensitive setup given the time of year
with lack of sub-freezing temps and dynamic cooling being
necessary to support heavier snowfall rates. WPC probabilities show
10-20% chances for snowfall >2" in the tallest peaks of the
Catskills, Adirondacks, Green, and White Mountains through Saturday
morning.


WPC probabilities for ice accumulations above 0.1" throughout the
CONUS are less than 10%.


Mullinax



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FOUS11 KWBC 100809
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Thu Apr 10 2025

Valid 12Z Thu Apr 10 2025 - 12Z Sun Apr 13 2025


...Great Lakes & Interior Northeast...
Days 1...

Light snow is expected this morning across portions of north
central PA into southwest NY. Marginal temperatures support mostly
rain by mid morning, but before then areas could see a coating to
inch of accumulation. As the system moves slowly east do expect
more coverage of light snow by tonight as temperatures cool over
eastern NY into New England. Guidance has trended a bit cooler,
and so anticipate the ptype to become mainly snow or a rain snow
mix overnight, with the exception of coastal areas which will most
likely stay rain. Most areas will pick up a coating to inch of
snow, although probabilities of exceeding 2" have increased over
the Berkshires, southern Green Mountains, Catskills and southern
Adirondacks, with a 40-60% of amounts locally exceeding 2".


...New York into New England... Day 2 and 3...

A large scale trough and developing closed low will bring another
round of precipitation to the Mid-Atlantic and Northeast Friday
into Saturday. More uncertainty with the details of this system,
with notable spread in the 00z guidance. The general trend has
been a further south and east track of the developing low, likely
making this a colder system. However temperatures will still be
marginal, and any axis of notable accumulating snowfall will
probably be rather narrow on the northern periphery of the
precipitation axis. The 00z GFS is the most aggressive solution,
bringing ample precipitation into the colder airmass resulting in
a more significant snowfall solution from eastern NY into northern
New England. On the other end of the model spectrum some solutions
have trended far enough south and east to result in a suppressed
enough solution that little to no precipitation falls in the form
of snow. The most likely scenario is in between this more
suppressed solution and snowier GFS solution.

The expectation is that precipitation lifting north into the
colder air will be snow by later Friday night into Saturday
morning. While some mix with snow is possible in lower elevations,
the best chance of accumulating snow will be in areas of
terrain...with the Catskills, Berkshires, Green Mountains and the
Worcester Hills into the White Mountains the most favored areas.
The probabilities of 2" have increased over these areas, generally
in the 50-80% range, with 4" probabilities over 40% on a localized
basis. A solution in between the 00z GFS and ECMWF (closer to the
ECMWF) best aligns with this axis of higher probabilities...with
the 00z AIFS also well aligned with the current WPC forecast. The
00z ECMWF being a bit further south brings more accumulating
snowfall into the Poconos of northeast PA into portions of
northwest NJ. While this is a lower probability outcome it can not
be ruled out, thus some chance amounts over these areas see some
upward adjustment in future forecasts.


...Cascades to Northern Rockies...
Day 1-3..

Periods of light to moderate snow area expected over the Cascades
today through saturday, with snow levels lowering with time. Some
accumulating snowfall is likely as low as around 2,000 feet, with
total snowfall over 6" expected in the more favored terrain areas.

A strong mid level shortwave moving across the Northwest will
bring a snow threat to the Northern Rockies by Saturday into
Saturday night. Southerly flow ahead of this shortwave will result
in a warm system initially, with most snow falling above 6,000
feet. However behind the shortwave temperatures will rapidly drop,
resulting in lowering snow levels and bringing the threat of some
accumulating snowfall to more of central MT. More uncertainty with
this lower elevation snowfall as model differences in the low
track and strength will impact the amount of precipitation on the
cold side of the system. So the greater confidence for
accumulating snowfall remains over the higher terrain over 6,000
feet, with probabilities of exceeding 6" through 12z Sun as high as
50-80% over the Little Belt Mountains and the Lewis and Swan
Ranges of northwest MT.

Chenard

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FOUS11 KWBC 110646
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
246 AM EDT Fri Apr 11 2025

Valid 12Z Fri Apr 11 2025 - 12Z Mon Apr 14 2025


...Northern Mid-Atlantic to New England...
Days 1-2...

Ongoing light snow this morning will taper off just after 12Z, but
will then turn to the next area of wintry weather later tonight
into Saturday. Upper trough axis will slowly approach the East
Coast with front-side/downstream upper low development over the
Mid-Atlantic. This will favor another surge of moisture northward
into marginally cold air over the Northeast/northern Mid-Atlantic
as mostly snow to the north away from the coast (roughly south of
I-90/I-84) but perhaps a small area of sleet as well. Ptypes will
be dependent on rates where temperatures are marginal, with some
areas alternating between rain/snow. In addition, accumulation may
be limited to grassy areas given mild ground/road temperatures and
also may be limited within a few hours of solar noon as we approach
mid-April. However, some more vigorous WAA over higher terrain
could yield several inches of snow on Saturday for places like the
Catskills, Berkshires, and southern Green/White mountains where WPC probabilities for at least 4 inches of snow are generally 20-50%.
The northern extent of the snow is still a bit in question as the
system tries to consolidate toward the Gulf of Maine Sunday before
moving out of the area.


...Cascades to Northern Rockies...
Day 1-3..

Broad SW flow this morning will continue light snow for the
Cascades today while the trough axis slowly approaches out of the
northeastern Pacific. By Saturday, a stronger mid-level shortwave
will come into WA and strengthen across ID/MT, promoting light to
modest WAA-driven snow over NW MT into northern WY as the upper jet
slips southeastward into the Plains. Temperatures will fall behind
the front and lower snow levels to below 4000ft as precipitation
lightens and then ends from west to east on Sunday/Sunday night.
The system will be fairly progressive but it could snow moderately

1"/hr) for a time Saturday evening. WPC probabilities for at

least 8 inches of snow for the period are highest around Glacier NP
and across the Little Belt Mountains (>50%).


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso


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FOUS11 KWBC 120644
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
244 AM EDT Sat Apr 12 2025

Valid 12Z Sat Apr 12 2025 - 12Z Tue Apr 15 2025


...Northern Mid-Atlantic to New England...
Day 1...

Storm system just off the DelMarVa this morning will continue to
lift northeastward to a position just east of Cape Cod by early
Sunday morning. With an amplified jet, moisture already across much
of the northern Mid-Atlantic into the Northeast will turn to snow
as temperatures cool just enough on northeasterly surface flow.
Snow will pick up in intensity toward daybreak, and by the start of
this period (12Z Sat), moderate snow is likely (rates >1"/hr) over
parts of the Catskills, Berkshires, and Green and White Mountains
through mid-day. By this afternoon, drier air toward the mid-levels
will help decrease any snow or rain/snow mix across much of the
area except for northern New England where temperatures will rise
to around freezing where snow continues to fall. Precipitation will
mostly end by early Sunday but continue over northern Maine into
the afternoon. WPC probabilities for at least 4 inches of snow are
highest (>50%) over the higher elevations above 1000-1500ft or so
with 1-3" over lower elevations and a rain/snow mix with little
accumulation in the lowest elevations (valleys and near the water
south of I-90).


...Northern to Central Rockies...
Days 1-2...

A strong mid-level shortwave over WA this morning will strengthen
across ID/MT today, promoting light to modest WAA-driven snow over
NW MT/northern ID into northern WY as the upper jet slips
southeastward into the Plains. Temperatures will fall behind the
front and lower snow levels to below 4000ft as precipitation
lightens and then ends from west to east on Sunday/Sunday night. By
then, the cold front will slow across the central Rockies, helping
to wring out some snow over CO. The system will be fairly
progressive overall but it could snow moderately (>1"/hr) for a
time this evening over NW MT and NW WY. WPC probabilities for at
least 6 inches of snow for the period are highest around Glacier
NP, across the Little Belt Mountains, and near Yellowstone NP
(30-60% probs). Over the CO Rockies, amounts will be lighter
overall, but some areas could still see several inches of snow
(above 10,000ft). There, WPC probabilities for at least 6 inches of
snow are 40-60%.


...Western Great Lakes...
Day 3...

The mid-level low exiting MT Sunday will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure will deepen and help foster an expanding
area of precipitation over the northern Plains into the Upper
Midwest. Temperatures will be marginal to mild initially, but once
the low tracks into Lake Superior, north to northwest winds will
bring in colder air to northern areas of MN and eventually into the
U.P. of Michigan Monday night into early Tuesday. Snow will become
more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. of Michigan. There, WPC
probabilities for at least 4 inches of snow through 12Z Tue are
moderate (40-70%).


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso


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FOUS11 KWBC 130710
QPFHSD

Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
310 AM EDT Sun Apr 13 2025

Valid 12Z Sun Apr 13 2025 - 12Z Wed Apr 16 2025


...Maine...
Day 1...

Upper trough will finally start to push east of 70W today with the
last wave lifting toward the Gulf of Maine. Rain along the coast
and snow inland will slowly ease out of the area overnight tonight
into early Monday, with some modest QPF amounts that have trended
up in just the past 24 hrs (with a slower exit of the system
altogether). Temperatures remain marginal for most areas, but snow
should still accumulate over northwestern Maine and in the higher
elevations even during the daytime when precip rates may be
highest. Still, SLRs will be not much better than about 7-9:1,
making for a west and heavy snowfall. WPC probabilities for at
least 4 inches of snow after 12Z today are at least 40% over much
of northern Maine, with low probabilities (10-30%) of at least 8
inches in some of the highest elevations.


...Northern to Central Rockies...
Day 1...

A strong/compact upper low will move out of western MT this
morning, with some with some trailing snow along a surface trough
axis back toward the middle of the state that will end late this
afternoon. To the south, a weaker shortwave will move from UT to
CO, helping to wring out some snow for the high Rockies and lighter
snow below 7500ft as colder air comes in. WPC probabilities for at
least 4 inches of snow after 12Z today are moderate (40-70%)
across some of the central MT mountains (e.g., the Little Belts)
and over the northern CO Rockies (above 10,000ft).


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

The mid-level low exiting MT today will strengthen more over the
northern Plains as a 120kt jet streak develops over Iowa. An area
of surface low pressure at the tip of this jet will deepen over
northern WI and help foster an expanding area of precipitation
throughout the region. Temperatures will be mild initially (upper
50s into central MN/WI), but once the low tracks into Lake
Superior, north to northwest winds will rapidly bring in colder air
to northern areas of MN and eventually into the U.P. of Michigan
Monday night into early Tuesday. Rain will change to snow and
become more widespread with accumulation likely over most of the MN
Arrowhead and northern WI into the U.P. and northern Lower
Michigan. By Tuesday, with the surface low well into Ontario,
northerly winds will advect in 850mb temperatures of around below
-6C which may be enough to spur some lake enhancement (Lake
Superior temperatures around 4-5C). The snow will end from west to
east on Tuesday. WPC probabilities for at least 4 inches of snow
through 00Z Wed are moderate (30-60%) in northeastern MN. For
areas downwind of Lake Superior (far northern WI through the U.P.
of Michigan), higher amounts are likely Monday night through
Tuesday, with WPC probabilities depicting 20-60% chances for at
least 8 inches of snow in the favored areas just inland from the
lake shore and with any elevation (e.g., Porcupine and Huron
Mountains). For northern Lower MI, WPC probabilities for at least
4 inches of snow are low (10-30%).


...The Northeast...
Day 3...

Low pressure will continue through Canada with its cold front
rushing across the Northeast on Tuesday. Behind it, colder air will
filter in with lingering precipitation downwind of the eastern
Great Lakes with some upslope in the central Appalachians as well.
Temperatures will be marginal for some lower elevations and also
near the lake waters, but light accumulation is likely over much of
western and northern NY (Chautauqua Ridge, Tug Hill Plateau,
Adirondacks). There, WPC probabilities for at least 4 inches of
snow are 10-60%, highest in the Adirondacks.


The probability of at least 0.10" of freezing rain across CONUS is
less than 10%.


Fracasso




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