• HVYSNOW: US Winter Storm

    From Dumas Walker@21:1/175 to All on Sunday, January 14, 2024 09:00:00
    FOUS11 KWBC 140950
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    450 AM EST Sun Jan 14 2024

    Valid 12Z Sun Jan 14 2024 - 12Z Wed Jan 17 2024

    ...Prolonged Great Lake Effect and Snow Squalls in Northeast today...
    Days 1-3...

    A slow moving and sprawling low pressure gyre centered over
    northern Ontario develops today and likely persists there into
    midweek as a powerful trough axis swings over the Northeast today.
    This means a prolonged WSW to W wind lake effect snow event
    downwind of all five Great Lakes that have a few ebbs and flows
    through this time. Cold air through the column (850mb temps <-18C)
    over the still nearly unfrozen lakes will lead to more than steep
    enough lapse rates for snow, but the cold air will generally favor
    lower than maximum SLRs (past the DGZ on the cold end) also from
    dendritic fracturing in the gusty winds today.

    Snow squalls (a brief burst of snow accompanied by winds and a
    real threat to overland travel) are expected from the upper trough
    axis moving over much of PA/NY this morning through midday,
    shifting across the northern the northern Mid-Atlantic and
    southern/central New England all the way to the coast this
    afternoon/evening. Snow squalls are most dangerous when
    temperatures fall below freezing with the squall, causing a flash
    freeze on roadways and this looks to be the case this afternoon
    over eastern PA/northern NJ/southern NY and southern New England.

    LES snow probs: Day 1 for at least 6 inches of snow are high
    70%) over the eastern U.P. of Michigan and especially in the
    single band setups east of Lakes Erie/Ontario in WSW flow
    (favoring near and just south of BUF) where double-digit totals
    are quite likely.

    Tonight into Monday, flow becomes westerly across the western
    Lakes, supporting multi-bands into much of Lower Michigan but
    still some single bands into the Keweenaw Peninsula on the U.P.
    where WPC probabilities for at least another 4 inches are around
    50%. Intense single bands off Erie/Ontario will waver a bit and
    lift northward but weaken, still allowing for several more inches
    of snow with high probs for >6" in narrow bands north of Buffalo
    and the Tug Hill. Westerly flow prevails Tuesday into Wednesday
    with Day 3 probs moderate for additional >6" in the Keweenaw and
    back over Buffalo/the Tug Hill

    ...Mid-South/TN Valley/Deep South/Appalachians through Northeast...Days 1-3...

    A series of impulses is lined up from the Four Corners to the
    OR/CA coast early this morning. These will ride a WNWly jet that
    rounds the longwave trough spanning most of the CONUS. That jet
    turns Wly and increases to 130-kt jet over OK to the Mid-Atlantic
    tonight with the Mid-South in the right entrance region aiding
    lift as these impulses/vort maxes push through. Arctic front will
    reach the upper TX coast this morning and the central Gulf Coast
    by this evening, bringing sub-freezing temperatures in its wake
    from eastern TX through the Lower MS Valley. However, low level
    ridging over the Gulf will allow return flow north over the
    Arctic-sourced airmass in place, setting up a broad area of a
    wintry mix of sleet and freezing rain tonight through Monday night
    from east Texas across much of LA and central MS/AL. Farther north
    in the deeper cold air, light to locally moderate snow will expand
    eastward intermittently with the impulse arrivals from central OK
    and through AR this morning through this evening before settling
    on a low level frontogenetic zone from southern AR east-northeast
    over northern MS/most of TN to the southern Appalachians tonight
    through Monday. Along this zone, expect moderate to possibly heavy
    snowfall with relatively high SLRs (~12-16:1). This focus has
    shifted south a bit with the 00Z consensus tonight with the stripe
    of several inches of snow now more over south-central AR and
    northern MS, but still extending ENE across TN and far northern
    AL. How far north the warm air aloft reaches will determine the
    north area of the sleet area progresses, current thinking is the
    NAMnest remains too far north into with the warm nose, especially
    with the rest of 00Z guidance shifting south. Snow should be
    heaviest just north of the sleet area making the warm nose
    progression key to a decent forecast. Day 1.5/2 WPC probabilities
    of at least 4 inches of snow are moderate (40-70%) over a stripe
    from southeast AR through northern MS and most of TN and then up
    the southern Appalachians into WV.

    Farther south, cold surface temperatures beneath a warm nose aloft
    supports an area of freezing rain/sleet starting this evening from
    the TX Hill Country/South-central TX eastward across much of LA
    through central MS and into AL. It will be a battle between the
    arctic air beneath the advancing warmer air aloft, and the latest
    guidance with potential for freezing rain accumulations to or near
    the Gulf Coast given how cold the surface air is. In general, the
    northern portion of the wintry mix area is more confidently going
    to be sleet given the depth and magnitude of surface cold air. The
    Day 1.5 WPC probabilities of at least 0.10" ice are moderate
    (30-60%) from around I-35 between San Antonio and DFW eastward
    into central MS (I-55) with little to no chances for 0.25" at this
    time. The Day 1/2 chance of any (>0.01") icing (>10% chance)
    extends from south TX across east TX nearly all of LA (outside
    NOLA) through much of MS, central AL, and northwest GA into far
    eastern TN.

    A shortwave trough rounding the longwave pushes down the northern
    Rockies tonight before shifting east over the Ohio Valley into
    Tuesday and the Northeast Tuesday night. This would promote
    coastal low development off the northern Mid-Atlantic late Tuesday
    and past New England Tuesday night. Day 3 snow probs for >4" are
    low over the northern Mid-Atlantic, but become moderate (40-60%)
    over Down East Maine. Uncertainty remains with the strength of
    this low, but probabilities are increasing for the first inch of
    snow of the winter to some of the I-95 corridor (DC-PHL-NYC) where
    the snow drought continues.

    ...Great Basin and Colorado Rockies... Days 1-2...

    The last impulse in a series of waves moving into OR starting
    Saturday cross the coast at the OR/CA border around 12Z today and
    tracks inland along/south of a stationary front marking the south
    border of the Arctic sourced air that invaded the Northwest.
    Mountain snows continue over the Great Basin ranges, the Wasatch
    and Colorado Rockies as noted by the Day 1 snow probs which are
    high for >6" for the Wasatch and most CO ranges.

    Ridging shifts inland behind this last impulse, cutting off precip
    quickly today for the West Coast and by Tuesday for the Rockies.
    However, a northern stream shortwave trough rounding the deep low
    gyre developing over Ontario will shift down the northern Rockies
    tonight into Monday providing lift and extending snow over the
    central Rockies (with light snow extending east onto the Plains
    across KS) with some low to moderate Day 2 snow probs for an
    additional >6" for the central CO Rockies.

    ...Northwest... Day 3...

    The next compact low to cut east through the Northeast
    Pacific/Alaska ridge likely reaches the OR/WA coast late Tuesday
    and may be joined by northern stream troughing shifting south from
    BC Tuesday night into Wednesday allowing a quick shift inland to
    the northern Rockies Tuesday night. With anomalously cold surface
    air likely lingering over the Pacific Northwest including Seattle
    and Portland metros, a wintry mix to sea level is in the cards.
    Day 3 PWPF are 10-50% for >0.1" ice along the western OR/WA border
    including the Portland metro and 20-60% for >6" over the WA
    Cascades as well as eastern WA/northern ID and the Sawtooths
    toward the Boise metro in west-central ID. This low/wave combo
    looks to be the first part of a rather active winter weather
    pattern for the Northwest continuing the rest of the week.

    Jackson


    ***Key Messages for Mid-January Arctic Blast, Lake Effect, and Snow Squalls***

    --Dangerously Cold Wind Chills Expected
    Sub-zero wind chills will affect much of the U.S. and reach into
    portions of the South. Wind chills into early this week will fall
    below minus 30 degrees from the northern Rockies to the central
    Plains and mid Mississippi Valley. Values will drop as low as
    minus 70 degrees from Montana to North Dakota. These wind chills
    will pose a risk of frostbite on exposed skin and hypothermia.
    Have a cold survival kit if you must travel.

    --Lake Effect Snow Persists This Weekend
    Heavy snow will continue downwind of the Great Lakes into midweek.
    Whiteout conditions in the lake effect snow bands are expected.
    An additional 12-24 inches of snow will occur through Monday
    across portions of western and northern New York.

    --Snow Squalls Expected over the Northern Mid-Atlantic and
    Northeast Today
    Snow squalls will impact portions of the northern Mid-Atlantic and
    Northeast today. Gusty winds, rapidly reduced visibility, and
    flash freezing on roads will result in dangerous travel where
    squalls occur.

    --Hazardous Cold Weather to Persist and Redevelop
    A new surge of Arctic air will drop south over the northern Plains
    and Midwest midweek, reaching the Deep South by the end of the
    week. This will reinforce dangerously low temperatures and wind
    chills.


    ***Key Messages for Western U.S. to Mid-South Winter Storm***
    --Heavy Snow Impacting the Intermountain West
    Heavy snow will taper down along the West Coast this morning and
    focus over the Wasatch of Utah and the Colorado Rockies today
    where continued significant impacts are expected.

    --High Avalanche Danger Continues for Portions of the Sierra
    Nevada and the Rockies
    Heavy snowfall and strong winds have created dangerous avalanche
    conditions across portions of the Sierra Nevada and the northern
    to central Rockies. Travel in, near, or below avalanche terrain is
    not recommended.

    --Snow and Ice to Reach the Southern Plains Later Today and the
    Mid-South Tennessee Valley Tonight and Monday
    Areas of snow, sleet, and freezing rain are likely to develop and
    spread across portions of the southern Plains, through the
    ArkLaTex, and into the Tennessee Valley today through Monday.
    Several inches of snow are likely. Accumulating ice is expected
    from portions of central and southern Texas through the Lower
    Mississippi Valley into portions of the Tennessee Valley. With
    Arctic air continuing to filter south this week, impacts from
    wintry weather may last for several days, resulting in a prolonged
    period of hazardous travel.

    $$
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  • From Dumas Walker@21:1/175 to All on Monday, January 15, 2024 08:39:00
    FOUS11 KWBC 151012
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    511 AM EST Mon Jan 15 2024

    Valid 12Z Mon Jan 15 2024 - 12Z Thu Jan 18 2024

    ...East Texas, Lower MS Valley, Deep South, TN Valley,
    Appalachians through Northeast... Days 1-3...

    A vort max over the TX Panhandle will zip east today on the tail
    of a potent WSWly jet which will promote further low level
    moisture flow from the western Gulf and produce light precip over
    south-central and East TX through the Deep South. Surface cold air
    advection will continue to bring these areas below freezing with a
    light glaze likely through this swath and 20% probs for >0.1" ice
    over east TX/northern Louisiana/central MS as well as far
    northeast AL/northwest GA.

    To the north, the arctic air will be much deeper, supporting all
    snow from eastern AR eastward across northern MS and through much
    of TN and the southern Appalachians. Relatively high SLRs
    (~12-16:1) would favor several inches of snow that will continue
    to be enhanced by frontogenetical banding as the entire system
    shifts eastward ahead of a sharpening trough axis rounding the
    sprawling low centered up over Ontario. Day 1 snow probs for >4"
    are 40%-70% from eastern TN up far western VA into central WV with
    lower probs over the northern VA Blue Ridge and north-central MD.

    Coastal low development off the Mid-Atlantic coast begins late
    tonight which quickly rides north in the right entrance to the
    intensifying SWly jet just inland of the Northeastern Seaboard.
    Day 1.5 snow probs for >4" are around 20% for eastern PA/northern
    NJ/southern NY into southwest New England and then they increase
    farther north for Day 2 probs with northern and eastern Maine
    generally 40-60% where the coastal low is rapidly deepening as it
    moves north just off the New England coast.

    ...Colorado Rockies onto Central High Plains... Day 1...

    Shortwave trough rounding sprawling/deep low centered over
    northern Ontario shifts southeast over the CO Rockies today before
    swinging east over the central Plains this evening. 1050mb surface
    high pressure is on its heels this morning over northern MT. Snow
    continues through this afternoon over the CO Rockies with light to
    locally moderate snow bands shifting east in the strengthening Wly
    jet across KS/MO/IL/IN today through tonight. Day 1 snow probs are
    40-60% for an additional >6" on the central CO Rockies with low
    probs for >2" east from the Palmer Divide across KS.

    ...Prolonged Great Lake Effect Snow... Days 1-3...

    Expansive upper low established itself over far northern Ontario
    today and lingers through Wednesday. A wrapping vort/wave crosses
    the Great Lakes from west to east this evening through Tuesday.
    The prolonged cyclonic flow across the Great Lakes maintains the
    multi-day lake effect snow with NWly flow and multi-bands over the
    western Lakes and Wly to WSWly flow and single bands for the
    eastern Lakes. Robust single bands off Lakes Erie/Ontario continue
    for nearly all typical lake belts, with minor variations
    continuing as well as some disruption from the vort passage
    Tuesday morning. PWPF do not handle the small phenomena of LES
    well, but for the Erie/Ontario single bands, Day 1 is generally
    north of Day 2 as the flow veers more from WSWly to Wly. Day 3 is
    back north a bit and much more intense with high probs for >8" off
    both. Otherwise, it's the Keweenaw Peninsula that gets enough snow
    Days 1/2 to show up in the PWPF.

    ...Northwest... Days 2/3...

    A one-two punch of mid-level waves reaches the Pacific Northwest
    late Tuesday and on Wednesday. The first is a southern stream
    compact low that slices east through the northeastern Pacific
    ridge and the second is a sharp northern stream trough that slowly
    shifts south down the Alaskan Panhandle tonight/Tuesday and the BC
    coast Tuesday night/Wednesday before shifting southeast down the
    northern Rockies Wednesday night. Ample moisture plume leading the
    compact low surges inland across the PacNW coast Tuesday to the
    northern Rockies Tuesday night with snow levels shooting up to
    8000ft by Tuesday evening, though these quickly drop below 5000ft
    under the low Tuesday night.

    However, the Arctic-sourced air that remains over northern
    OR/western WA will persist under the milder air aloft move into
    the region Tuesday. A wintry mix of snow/sleet to freezing rain is
    likely over the lower Columbia area including the Portland metro
    where Day 2 ice probs for >0.1" ice are 30-60% along with 10-20%
    probs for >0.25" ice.

    Farther inland, deep cold air will remain entrenched which favors
    higher SLRs with Day 2 snow probs for >6" 10-40% over the WA
    Cascades and the Sawtooths near Boise. Then the second wave moving
    into the interior Northwest late Wednesday will further aide the
    inland surge of Pacific moisture with widespread mountains snows
    over the Cascades and northern/central Rockies where day 3 snow
    probs for >6" are 40-60%. Day 3 probs for >12" are 50-90% for the
    WA Cascades and the Bitterroots.

    Jackson


    ***Key Messages for Southern and Eastern Winter Storm***

    --Southern Wintry Mix Continues Today
    Areas of sleet and freezing rain will continue to impact areas
    from south-central Texas through the lower Mississippi Valley and
    into eastern Tennessee. With arctic air in place hazardous travel
    can be expected.

    --Snow over the Southern Appalachians through Mid-Atlantic today
    into Tuesday
    Areas of snow will continue over Tennessee, the southern
    Appalachians and Mid-Atlantic today into Tuesday. Plan on slippery
    roads and difficult travel conditions.

    $$
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  • From Dumas Walker@21:1/175 to All on Monday, March 25, 2024 08:41:00
    FOUS11 KWBC 250813
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    413 AM EDT Mon Mar 25 2024

    Valid 12Z Mon Mar 25 2024 - 12Z Thu Mar 28 2024

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

    An inverted 500mb trough over the Southern Rockies will be the
    focus for additional heavy snow today. The Sangre De Cristo and
    eastern San Juans both sport high chances (>70%) for additional
    snowfall totals >8" with the tallest peaks of the Sangre De Cristo
    in northern New Mexico even having moderate-to-high chances
    (50-70%) for >12" snowfall accumulations through Monday afternoon.
    The axis of moisture and lift associated with this upper trough
    will even result in heavy snow over the Gila Mountains in eastern
    Arizona. WPC PWPF shows moderate chances (40-60%) for snowfall
    accumulations >8" through Monday evening. The 500mb trough will
    eject east into the Southern Plains Monday night, thus all but
    concluding the lingering periods of snow by Tuesday morning.

    ...Northern Plains & Upper Midwest... Days 1-2...

    The major winter storm will be well underway with the worst impacts
    being felt from the central High Plains on north to north-central
    Minnesota. The deformation axis on the northern and western flank
    of the storm will be capable of producing 1-2"/hr snowfall rates to
    go along with wind gusts that are exceeding 40 mph in northwest
    Kansas, central Nebraska, and southeast South Dakota. Farther east,
    the impressive 850mb WAA in the Upper Mississippi Valley that was
    in part responsible for the heavy snowfall overnight will lead to
    a burgeoning warm nose at low levels that causes snow to
    changeover to a wintry mix this morning in southern Minnesota,
    northern Wisconsin, and the Michigan U.P. By this afternoon, any
    lingering wintry mix is expected to transition over to plain rain.
    Meanwhile, the storm will continue its trek northeast into the
    Upper Mississippi Valley Monday evening with heavy snow enveloping
    eastern South Dakota, northern Minnesota, and the Minnesota
    Arrowhead.

    Snow will continue to fall heavily over north-central Minnesota
    Monday night with some residual snow as far south as eastern
    Nebraska and northern Kansas as a TROWAL pivots overhead. By
    Tuesday morning, the low will be tracking into northern Wisconsin
    with heavy snow across northern Minnesota and a mix of heavy
    snow/wintry mix along the Minnesota Arrowhead. The storm will then
    move over the U.P. of Michigan Tuesday afternoon, then finally into
    southern Ontario Tuesday night. Snow will continue to fall across
    northern Minnesota and portions of far northern Wisconsin and the
    western Michigan U.P. Heavy snow will effectively come to an end by
    Wednesday morning with just lingering snow showers along the
    Minnesota/Canada border and along the northern coast of the
    Michigan U.P..

    WPC PWPF shows moderate-to-high chances (50-70%) for additional
    snowfall >6" from north-central Nebraska and eastern South Dakota
    to far southeast North Dakota, northern Minnesota, and the
    Minnesota Arrowhead. South-central South Dakota and the Minnesota
    Arrowhead even show low chances (10-30%) for additional localized
    snowfall amounts >8". Farther southwest, WPC PWPF shows moderate-
    to-high chances (50-70%) for additional snowfall totals >4" in
    southwest Nebraska, northwest Kansas, and southeast Colorado.
    Nebraska and northwest Kansas, in particular, could contend with
    blizzard conditions due to prolonged high wind gusts and
    significantly reduced visibilities.

    ...Pacific Mountains Ranges... Days 2-3...

    Outside of some diurnally driven snow showers and weak onshore
    flow in the Pacific Northwest through Tuesday night, little in the
    way of heavy snowfall is likely to occur for many of the mountains
    ranges along the West Coast. That finally changes by early
    Wednesday morning as the next Pacific storm system approaches and
    directs a slug of Pacific moisture first at the Pacific Northwest,
    then into the Northern California ranges and interior Northwest
    ranges Wednesday night. The IVT is a quick mover but a fairly
    potent IVT sporting values >400 kg/m/s just off the California
    coast. Overall, the peak of the IVT tracking into northern
    California Wednesday afternoon is likely to top the 97.5
    climatological percentile, supplying not only abundant moisture to
    the region but strong upslope enhancement (especially in the Sierra
    Nevada). Snow levels in the Sierra Nevada will initially start out
    as high as 6,500ft, but gradually fall to 5,000ft by Thursday
    morning as the cold front pushes through. Farther north, snow
    levels will start out around 5,000ft in the northern California
    ranges (Salmon/Siskiyou/Trinity) and closer to 4,500ft in the OR/WA
    Cascades, but those too will fall an additional 2,000ft by
    Thursday AM. Latest WPC PWPF shows high chances (>70%) for snowfall
    amounts >8" in the Northern Sierra Nevada >6,000ft and in the
    northern California ranges, while only the volcanic peaks of
    southern Washington and the Olympics sport similar high chances
    for >8" of snowfall through early Thursday morning. Some snow will
    spill over into the Blue Mountains and the Boise/Sawtooth late
    Wednesday night into Thursday with low-to-moderate chances (30-50%)
    for snowfall totals >6" through early Thursday morning.

    Mullinax


    ***Key Messages for Plains-Upper Midwest Winter Storm***

    --A high-impact winter storm unfolding

    A powerful storm system will impact the Northern/Central Plains
    into the Upper Midwest through Tuesday. Periods of snow and gusty
    winds will continue from the Central Plains to northern Minnesota,
    along with some sleet and freezing rain in parts of the Upper
    Mississippi Valley.

    --Widespread heavy snow expected

    Snow accumulating at rates of 1-2"/hr in heavier bands are
    expected from central Nebraska and eastern South Dakota to northern
    Minnesota. Additional snowfall totals between 6-12" are forecast
    from central Nebraska to northeastern Minnesota.

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

    Heavy snow and gusty winds approaching 50 mph will produce
    blizzard conditions with near zero visibility into Tuesday morning.
    Travel could be nearly impossible at times. Power outages and tree
    damage are likely in some areas due to the heavy and wet snow
    combined with icing and strong winds.


    $$
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