• Major US Winter Storm

    From Dumas Walker@21:1/175 to All on Sat Mar 23 09:03:00 2024
    FOUS11 KWBC 230810
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    410 AM EDT Sat Mar 23 2024

    Valid 12Z Sat Mar 23 2024 - 12Z Tue Mar 26 2024

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

    This morning, heavy snow is underway from northern New York to much
    of interior New England. Strong 850-700mb FGEN aloft coinciding
    beneath the right-entrance region of a strengthening 250mb jet
    streak over southern Quebec is aiding in the formation of distinct
    heavy snow bands setting up from the Tug Hill and Adirondacks to
    the Green and White Mountains. As the day unfolds, another jet
    streak along the Mid-Atlantic coast will intensify and place its
    diffluent left-exit region over New England through Saturday
    evening. This "kissing jets" setup forces vertical ascent at mid-
    upper levels of the atmosphere to become exceptionally strong,
    while simultaneously, a 40-50 knot southerly 850mb jet is
    directing copious amounts of moisture poleward towards New England.
    Add in a sufficiently cold air-mass from the Tug Hill on north and
    east through central and northern Maine, and the stage is more
    than set for prolific snowfall rates producing a heavy, wet
    snowfall over northern New England.

    It is worth noting surface temperatures are likely to remain <32F
    from the southern tier of New York and even as far south as the
    Poconos to result in some minor ice accumulations. Latest guidance
    has the surface-925mb layer remaining colder longer and thus
    allowing for a longer period of freezing rain. The areas with
    moderate-to-high chances (50-70%) for ice accumulations greater
    than a tenth of an inch are the Berkshires, the Green, the
    Monadnock and Merrimack Valley of southern New Hampshire, and
    south-central Maine. Ice accumulations will be most likely confined
    to trees, bushes, and power lines, while sidewalks and side roads
    may also see some slushy accumulation during the day. The bigger
    impact lies in the snowfall, however, as the WPC Snowband
    Probability Tracker (SPT) shows snowfall rates of 2-3"/hr are
    anticipated Saturday afternoon and into Saturday night across
    northern New England. The WSSI shows Major Impacts (largely due to
    Snow Amount and some cases of Snow Load) from the Adirondacks and
    the Green and White Mountains through the heart of Maine. Areas
    under Major impacts can expect considerable disruptions to daily
    life that include dangerous, to even impossible, travel conditions,
    widespread closures and disruptions, and given the dearth of
    heavy, wet snow expected, the potential for tree damage and power
    outages. WPC PWPF shows high chances (>70%) for snowfall totals
    12" across Vermont's Northeast Kingdom, northern New Hampshire,
    and northern Maine. Snow will conclude shortly after midnight as
    high pressure builds in from the west on Sunday.

    ...The West... Days 1-3...

    An upper low barreling into the Pacific Northwest will accompany a
    second upper level disturbance tracking into southern California
    to direct a slug of Pacific moisture into California and as far
    north as the Cascades. The combination of upper level diffluence
    along with strong topographically-enhanced snowfall rates will
    result in periods of heavy snow along the Sierra Nevada and in the
    Northern California mountain ranges (Siskiyou/Salmon/Trinity) at
    elevations >5,000ft. Periods of heavy snow will also occur in parts
    of the Cascades (>5,000ft) and in the Great Basin (elevations
    7,000ft). By Saturday night, snow will advance east towards the
    Wasatch, the Mogollon Rim, the western Colorado Rockies, and
    northern New Mexico Rockies. Heavy snowfall along the Mogollon Rim
    will generally occur at elevations >7,000ft, while the Wasatch,
    Uinta, Colorado and northern New Mexico Rockies will witness heavy
    snow at elevations >8,000ft. The Sierra Nevada and Northern
    California ranges sport locally moderate-to-high chances (50-70%)
    per WPC PWPF for snowfall totals >12". There will likely be some
    portions of these mountains ranges that surpass two feet of snow as
    lingering upslope flow continues into Sunday. Snow will also
    linger through Sunday in the Four Corners region at elevations
    7,000ft before gradually dissipating by Monday morning.

    ...Northern Rockies & High Plains, Central Rockies, Upper Midwest...
    Days 1-3...

    **Major Winter Storm Set to Impact Northern/Central Rockies to
    Upper Midwest Beginning This Weekend**

    The upper low in the Pacific Northwest will spawn a new surface
    low in central Wyoming later this afternoon, while a strong dome
    of high pressure over south-central Canada and lower pressure in
    the Intermountain West maintains persistent easterly low-level
    upsloping flow into the northern High Plains and northern Rockies.
    This will keep periods of light snow falling in parts of eastern
    Montana and the western Dakotas, but snow accumulations will be
    more likely to occur on grassy surfaces, sidewalks, and side roads
    during the day. By Saturday night, low pressure will rapidly
    deepen over eastern Colorado. In response to the rapid pressure
    falls in the central High Plains, the 850mb LLJ will exceed 50kts
    over eastern Kansas and eastern Oklahoma. These southerly 850mb
    wind speeds are above the 99th climatological percentile and
    ushering in copious amounts of Gulf of Mexico moisture poleward
    into the Northern Plains and Upper Midwest through Sunday.

    By Sunday morning, heavy snow will be blanketing much of Montana
    with the main shield of snow gradually overtaking the Dakotas. The aforementioned 850mb moisture will wrap around the northern and
    northwestern flank of an elongated 700mb low located in central
    Nebraska. Strong 850-700mb FGEN over the Upper Mississippi Valley
    will result in heavy snow over southern Minnesota and northern Wisconsin
    that could produce 1-2"/hr snowfall rates Sunday afternoon and
    into Sunday evening. As the day unfolds the Central Plains will lie
    beneath the divergent left-exit region of a 250mb jet streak
    centered over northern Mexico, while to the north, the right-
    entrance region of a 250mb jet streak in southern Ontario further
    maximizes the intense vertical ascent atop the atmosphere. This
    will allow for the surface low on Sunday to deepen to
    exceptionally deep levels (sub 980 by Sunday evening). NAEFS at 00Z
    Monday shows much of southeast Colorado, the OK/TX Panhandles, and
    western Kansas sporting MSLP values that fall outside the observed
    1979-2009 CFSR database.

    Monday morning will see the strong 850mb warm air advection in the
    Upper Mississippi Valley ultimately lead to a changeover from snow
    to an icy wintry mix at first, then to all rain in southern
    Minnesota, northern Wisconsin, and the U.P. of Michigan. This will
    cut down on snowfall totals but the icy wintry mix in some areas
    could still cause hazardous travel Monday morning. Meanwhile, in
    central South Dakota, southeast North Dakota, and northern
    Minnesota, snow will remain the primary p-type with strong wind
    gusts >40mph causing blizzard conditions through Monday afternoon.
    Snow will liner along the Red River of the North and northwest
    Minnesota Monday night but rain will be the primary p-type in
    northern Wisconsin and the Michigan U.P..

    The latest WSSI shows Major Impacts in eastern South Dakota,
    southeast North Dakota, central Minnesota, and northwest Wisconsin.
    These areas sport moderate-to-high chances (50-70%) for snowfall
    totals >12" for the event, while areas near the northwest South
    Dakota and western Minnesota border have moderate chances (40-60%)
    for >18" of snowfall. WPC PWPF also shows high chances (>70%) for
    8" of snowfall in central South Dakota, along the Minnesota
    Arrowhead, and in northern Wisconsin. Farther south, as a strong
    cold front pushes through and upslope flow ensues, periods of
    moderate-to-heavy snow have moderate-to-high chances (50-70%) for
    producing >4" along the Colorado Front Range, the Palmer Divide,
    and on south along the Sangre De Cristo. Light snow accumulations
    are also possible in the High Plains of eastern Colorado and but
    wind gusts topping 50 mph could lead to significant blowing snow
    impacts. For more details on impacts, please review our latest Key
    Messages below.

    Mullinax


    ***Key Messages for Northern Plains Winter Storm***

    --A significant March winter storm begins today

    An extensive and high impact storm system will produce widespread
    heavy snow and gusty winds over the Northern Plains into the Upper
    Midwest beginning today and lasting into early next week.

    --Widespread heavy snow expected

    Heavy snow will spread across much of central and eastern Montana
    by Saturday night, then expand into the Northern Plains and Upper
    Midwest on Sunday and continue into Monday. There is a high chance
    70%) of at least eight inches of snow extending from portions of
    the Dakotas and north-central Nebraska northeastward through
    Minnesota into northern Wisconsin.

    --Hazardous impacts due to snow, snow load, and wind

    Heavy snow and gusty winds will produce areas of blowing and
    drifting snow and possible blizzard conditions Sunday into Monday.
    Hazardous travel, along with some disruptions and closures are
    expected late Saturday into early next week. Strong winds and
    heavy, wet snow on trees and power lines may result in tree damage
    and power outages.

    --Strong wind gusts in the Central and Southern Plains

    Blustery wind gusts in excess of 50 mph on Sunday may result in
    power outages, blowing dust that causes reduced visibility, and
    damage to property.

    $$
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  • From Dumas Walker@21:1/175 to All on Sun Mar 24 08:47:00 2024
    FOUS11 KWBC 240811
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    411 AM EDT Sun Mar 24 2024

    Valid 12Z Sun Mar 24 2024 - 12Z Wed Mar 27 2024

    ...The West/Four Corners... Days 1-3...

    A longwave trough encompassing most of the western U.S. will
    continue to produce rounds of heavy mountains snow today and into
    early Monday morning. While snow will be winding down in California
    throughout the day on Sunday, a vigorous 500mb vorticity max moving
    through the Four Corners region will induce PVA aloft and stream a
    plume of 850-500mb moisture flux into the Mogollon Rim, the Gila
    Mountains, the Wasatch, the Colorado Rockies, and both the Sangre
    De Cristo and San Juans of northern New Mexico. Snowfall rates will
    be heaviest in the Colorado and New Mexico Rockies where higher
    elevations >8,000ft will witness the best upslope enhancement. WPC
    PWPF shows high chances (>70%) for snowfall totals >8" in most of
    the Colorado and northern New Mexico Rockies, while probabilities
    are closer to moderate levels (40-60%) in the tallest peaks of the
    Wasatch, Mogollon Rim, and Gila Mountains. The WSSI shows Minor to
    Moderate Impacts throughout all these ranges through Sunday night,
    with the Gila and San Juans sporting some localized Major Impacts
    at their crests. Snow will gradually wind down Monday morning as
    the best upper level support moves east into the Plains, but some
    residual Pacific moisture throughout the West may result in
    localized moderate-to-heavy snow showers along the Rockies and as
    far west as the Great Basin. Meanwhile, a persistent onshore flow
    in the Pacific Northwest will produce some snow in the Cascades and
    Olympics on Monday, but snowfall rates will be manageable for these
    ranges. This may all change by Wednesday as the next Pacific storm
    system approaches the Washington coast with a renewed influx of
    Pacific moisture on its way that may bring more heavy snow to the
    Olympics, Cascades, and as far south as the Sierra Nevada.

    ...Northern Rockies & High Plains, Central Rockies, Upper Midwest...
    Days 1-3...

    **Major Winter Storm to Impact Northern High Plains to the Upper
    Midwest into Early This Week**

    This morning, a deepening surface low in eastern Colorado and a
    deepening 700mb low over western Nebraska will funnel copious
    amounts of Gulf of Mexico moisture northward into the Northern
    Plains and Upper Midwest. A deformation axis of snow will take
    shape over eastern Montana, northern Wyoming, and the Dakotas,
    while strong 850-700mb WAA generates thumping snow rates from
    northern Iowa and southern Minnesota to western Wisconsin. Latest
    WPC Snowband Probability Tracker (SPT) does depict snow bands that
    will likely produce 1-2"/hr snowfall rates late Sunday morning and
    into Sunday afternoon, with some cases where as high as 3"/hr are
    possible. As Sunday unfolds the Central Plains will located
    beneath the divergent left-exit region of a 250mb jet streak in
    northern Mexico, while the right-entrance region of a 250mb jet
    streak over southern Ontario maximizes the intense vertical ascent
    atop the atmosphere. This allows for the surface low in the Central
    Plains to drop to exceptionally deep levels (sub-980mb by Sunday
    evening). On the backside of the deepening 700mb low, strong
    northeasterly upslope flow and a potent cold front will allow for
    heavy snow to break out along the Front Range of the Colorado
    Rockies and the Palmer Divide Sunday evening, followed by the
    Sangre De Cristo and as far south as Raton Pass Sunday night into
    early Monday morning. Latest WPC SPT shows some instances where
    2-3"/hr snowfall rates may ensue with concerns of rapid snow
    accumulation on roads and significantly reduced visibilities into
    early Monday morning. Similar snowfall rates may occur in west-
    central Nebraska and northwest Kansas as the warm conveyor belt
    wraps around the northwest flank of the low. The ascent is so
    strong at low-mid levels that instances of thundersnow are possible
    Sunday night into Monday morning in some localized cases.

    Monday morning will see the storm system track northeast towards
    eastern Nebraska with strong 850mb WAA in the Upper Mississippi
    Valley ultimately causing a change over from snow to an icy wintry
    mix at first, then to all rain in southern Minnesota, northern
    Wisconsin, and the U.P. of Michigan by Monday afternoon. This will
    cut down snowfall totals but the icy wintry mix of sleet and
    freezing rain could still lead to hazardous travel conditions
    Monday morning. Meanwhile, in the eastern Dakotas and northern
    Minnesota, snow will remain the primary precip type with strong
    wind gusts >40 mph causing blizzard conditions through Monday
    evening. The expansive deformation axis of snow will pivot over
    these areas Monday night with snow also falling through eastern
    Nebraska and northern Kansas. By Tuesday morning, the storm will be
    over the Upper Mississippi Valley with the swath of heavy snow
    traversing much of Minnesota and the Upper Missouri river Valley.
    Snow will finally taper off from southwest to northeast Tuesday
    afternoon and be well into southern Canada by early Wednesday
    morning.

    The latest WSSI shows Major impacts in northeastern South Dakota,
    southeastern North Dakota, much of central Minnesota, and the
    Minnesota Arrowhead. These areas also sports high chances (>70%)
    for snowfall totals >12" for the duration of this winter storm.
    There are even low-to-moderate chances (30-50%) for >18" in
    northeast South Dakota and along the coast of the Minnesota
    Arrowhead. WPC PWPF also depicts high chances (>70%) for snowfall
    totals >8" in northern Nebraska, central South Dakota, and
    northwest Wisconsin. West-central Nebraska features moderate-to-
    high chances (50-70%) for >6" of snow to go along with whipping
    wind gusts surpassing 45 mph. Farther south, the Colorado Front
    Range, Palmer Divide, and Sangre De Cristo have moderate-to-high
    chances (50-70%) for >6" of snowfall through Monday morning. Expect
    hazardous travel in these affected areas Sunday and through Monday
    with blowing and drifting snow causing higher snow drifts and
    significantly reduced visibilities.

    Mullinax

    ***Key Messages for Northern Plains Winter Storm***

    --A high-impact winter storm unfolding

    An extensive storm system will continue to develop today,
    producing widespread heavy snow and gusty winds that will persist
    over parts of the Northern Plains and Central Plains as well as Upper
    Midwest through early this week.

    --Widespread heavy snow expected

    Heavy snow will expand into the Northern Plains and Upper Midwest
    today and continue into Tuesday. Heavy snow is also expected in
    parts of the Central Plains Sunday night into Monday. There is a
    high chance (>70%) of at least eight inches of snow extending from
    northern Nebraska and central South Dakota northeastward to
    central Minnesota and northwestern Wisconsin.

    --Hazardous impacts due to snow, snow load, and wind

    Heavy snow and gusty winds will produce areas of blowing and
    drifting snow and possible blizzard conditions Sunday into Monday.
    This will result in hazardous travel including road closures.
    Strong winds and heavy, wet snow on trees and power lines may
    damage trees and cause power outages.

    --Strong wind gusts in the Central and Southern Plains

    Wind gusts over 50 mph on Sunday may result in power outages,
    blowing dust with reduced visibility, difficult travel, and
    property damage. Critical fire weather conditions are forecast
    today over the Southern High Plains.

    $$
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