• HVYSNOW: Probabilistic He

    From Mike Powell@CAPCITY2 to All on Mon Oct 14 08:37:00 2024
    FOUS11 KWBC 140709
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    309 AM EDT Mon Oct 14 2024

    Valid 12Z Mon Oct 14 2024 - 12Z Thu Oct 17 2024

    ...Northeast...
    Days 1-2...

    An anomalous upper level trough over the Northeast will lead to a
    strengthening cyclone over northern New England this morning. The
    850mb low positioned over Upstate New York will track north and
    east through the Green and White mountains by this afternoon. To
    the north and west of the 850mb low, a surge in both moisture and
    NW winds will result in a stronger upslope component into the
    Adirondacks, Green, and White mountains throughout the day. In
    addition to the sufficient upper level ascent, an ari-mass that
    is quite cold by mid-October's climatology will support sub-
    freezing boundary layer temps for in the northern Appalachians. Locally
    heavy snowfall rates are expected with 0.5-1"/hr rates possible in
    the tallest peaks of the Adirondacks this morning and afternoon
    according to the 00Z HREF on WPC's Snowband Probability Tracker. As
    the storm tracks into Quebec this evening, snow will taper off and
    be limited to just snow showers through Tuesday morning. Another
    round of snow is likely to occur Tuesday late morning and through
    the afternoon as a trough axis pivoting on the back side of the
    storm system in eastern Quebec brings about an additional surge of
    low- mid level moisture. In addition, steep lapse rates could
    trigger potent snow showers, especially in the higher terrain of
    northern New England above 2,000ft. Snow showers look to linger in
    the northern Appalachians until Wednesday morning when the trough
    axis moves east and off the New England coast.

    Any locally heavy snowfall totals (>4") would likely be confined
    to elevations above 2,000ft in the Adirondacks, Green, and White
    mountains. WPC probabilistic guidance does depict some low-
    moderate chances (20-40%) for >6" of snowfall in the tallest
    3,000ft peaks of the Adirondacks. Below 2,000ft, snowfall amounts
    will struggle to top 2" in the 1,000-2,000ft elevation layer, with
    mainly a coating to 1" in the elevations below 1,000ft. Given this
    snowfall is the first of the season for parts of the region,
    motorists will be subjected to poor visibility and some snow
    covered roads for the first time in months. The WSSI-P does show
    low-moderate chances (20-40%) for Minor Impacts in parts of the
    Adirondacks through Monday evening.

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

    A 500mb shortwave trough bringing with it a surge in 850-700mb
    moisture and associated height falls will cause snow levels to
    gradually drop to as low as 4,000ft by Wednesday. The air-mass is
    not particularly cold for the time of year, so this setup favors
    snowfall accumulation in the Olympics and Cascades to elevations
    5,000ft. WPC probabilities do suggest low-moderate chances
    (20-40%) for >4" of snowfall on Wednesday along the windward side
    of the Cascade Range at elevations >4,000ft. As 500mb heights and
    snow levels continue to fall, some of the higher level Washington
    passes may start to see accumulating snow by Wednesday night. The
    potential for accumulating snowfall reaches the Northern Rockies
    (the Bitterroots, Absaroka, and Tetons most notably) by early
    Thursday morning. WPC probabilistic guidance suggests the Lewis
    Range of western MT could see locally higher totals surpassing 4"
    at elevations >7,000ft, while the other mountain ranges mentioned
    are most likely to see their best accumulating snowfall above
    8,000ft on Thursday.


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

    Mullinax


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Oct 15 09:07:00 2024
    FOUS11 KWBC 150737
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    337 AM EDT Tue Oct 15 2024

    Valid 12Z Tue Oct 15 2024 - 12Z Fri Oct 18 2024

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

    Following a brief tapering off of snowfall overnight, periods of
    snow will pick back up over the northern Appalachians Tuesday and
    linger into Tuesday night. This is due to an elongated upper level
    trough pivoting around the western flank of a closed 500mb low
    situated over the St. Lawrence Seaway that will traverse the
    Northeast from west to east. In addition to the usual upslope flow
    into the Adirondacks, Green, and White Mountains, the steep lapse
    rates aloft will trigger potent snow showers that could cause brief
    bursts of heavy snow at elevations >2,000ft. A few snow showers may
    linger around northern New England Wednesday morning, but
    accumulations would be minor and limited to the elevations >3,000ft
    on Wednesday. WPC probabilities show low chances (10-30%) for
    additional snowfall totals >4" along the higher elevations of the
    Adirondacks, Green, and White Mountains through Wednesday morning.

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

    An upper level shortwave trough bringing a surge in 850-700mb
    moisture and causing 500-700mb heights falls will cause snow levels
    to gradually drop from 6,000ft Tuesday night to around 4,000ft
    Wednesday evening over Washington's Olympic and Cascade Ranges. As
    this initial 500mb vort max exits to the east Wednesday night, a
    second trough will dive south through the region on Thursday with
    snow levels bottoming out just below 4,000ft in some cases. Periods
    of heavy snow are expected along the Oregon Cascades during the day
    on Thursday. Snow should taped off some time Thursday night. WPC
    PWPF showed high chances (50-70%) for snowfall totals >4" above
    5,000ft in the Cascade Range through Thursday.

    ...Northern & Central Rockies...
    Day 3...

    Pacific moisture out ahead of the first upper level shortwave to
    traverse the Pacific Northwest is forecast to produce periods of
    snow in the higher elevations (>6,000ft in northern ID, >7,000ft in
    the Bitterroots, Sawtooth, Absaroka, Tetons, Wind River, and Big
    Horn Ranges) early in the day on Thursday, but it is with the
    approach of the second trough where snowfall rates look to
    increase. Stronger height falls Thursday evening will accompany an
    air-mass that NAEFS shows at the 500mb and 700mb layers to be below
    the 10th climatological percentile. Plus, NAEFS shows an anomalous
    IVT that tops the 90th climatological percentile from the Great
    Basin to Utah. The region will also be placed favorably beneath a
    coupled jet structure that will help to maximize upper level
    divergence from the Absaroka on south to the Wasatch Thursday night
    and into Friday morning. Waves of low pressure will develop along
    a strengthening frontal boundary that will track through the
    Wasatch and into southern WY by Friday morning, prompting
    precipitation that starts out as rain to make a quick changeover to
    heavy snow.

    WPC PWPF sports moderate-to-high chances (50-70%) for >6" of
    snowfall in the Absaroka of southwest Montana with some moderate
    chances (40-60%) for >12" in some of the Absaroka's tallest peaks.
    Farther south, the Bighorns and Wind River Ranges sport low-
    moderate chances (30-50%) of seeing >8" of snowfall through 12Z
    Friday, while the Uinta how moderate-high chances (50-70%) for the
    same snowfall totals through 12Z Friday. This is likely to be the
    first winter storm of the season for these mountain ranges this
    season and will result in impacts residents have not dealt with in
    months (poor visibility, slick/snow covered roads). The WSSI-P does
    sport moderate-high chances (50-70%) for Minor Impacts in the
    Absaroka, Wind River, Big Horn, and Uinta ranges, as well as some
    of the tallest peaks of the Wasatch through Friday morning.


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


    Mullinax




    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Wed Oct 16 09:25:00 2024
    FOUS11 KWBC 160752
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    352 AM EDT Wed Oct 16 2024

    Valid 12Z Wed Oct 16 2024 - 12Z Sat Oct 19 2024

    ...Pacific Northwest...
    Days 1-2...

    An upper level shortwave trough ushering in a surge of 850-700mb
    moisture and resulting in upper level height falls will cause snow
    levels to gradually drop from 6,000ft early this morning to around
    4,000ft by Wednesday evening over Washington's Olympic and Cascade
    Ranges. As this initial 500mb vort max exits to the east Wednesday
    night, a second trough will dive south through the region on
    Thursday with snow levels bottoming out just below 4,000ft in some
    cases. The heaviest snowfall is likely to occur along the
    Washington Cascades Wednesday evening with moderate-to-heavy
    snowfall possible along the tallest peaks of the Oregon Cascades
    Thursday morning. WPC probabilities depict high chances (>70%) for
    4" of snowfall in the Washington Cascades and peaks above 5,000ft.
    The taller volcanic peaks of the Washington Cascades sport
    moderate-high chances (50-70%) for snowfall >8" through Thursday.


    ...Northern & Central Rockies...
    Days 2-3...

    **First Significant Winter Storm of the Season to Impact the
    Central Rockies**

    The evolution of the first significant winter storm of the season
    across portions of the Intermountain West begins as an upper level
    trough enters the Pacific Northwest on Thursday. As Thursday
    progresses, the upper trough will deepen as it tracks south through
    the Great Basin Thursday night, then becoming a closed low along
    the UT/AZ border by midday Friday. The low continues to slowly
    track across northern Arizona Friday night but remain stalled over
    the Four Corners region early Saturday morning.

    NAEFS shows upper level evolution that is quite anomalous from a
    variety of parameters. At 250mb, a jet streak over the northern
    High Plains will be coupled with a jet streak at the base of the
    amplifying upper trough, thus maximizing upper level divergence
    over the Intermountain West on Thursday. As the upper trough cuts
    off into an upper low by Friday, strong divergence beneath the left
    exit region of the 250mb jet streak will be placed over Utah and
    the Central Rockies. NAEFS shows 500-700mb heights and temperatures
    that are routinely below the 10th climatological percentile,
    particularly over the Great Basin and Utah late Thursday into
    Friday. Perhaps most impressive are the IVTs which will eclipse
    300 kg/m/s (above the 99th climatological percentile) in southern
    UT Thursday night. Mean flow out of the SW will result in strong
    upslope ascent into the Uinta and San Juans in particular.

    In the Absaroka, Big Horns, and Wind River Ranges, WPC PWPF shows
    high chances (>70%) for storm event snowfall totals >8" with at
    least moderate chances (>50%) for snowfall >12" in the tallest
    peaks. Farther south, the Uinta and San Juan sport high chances
    70%) for snowfall totals surpassing 12". In fact, the Uinta sport
    moderate chances (40-60%) for >18" of snowfall through Saturday
    morning, with high chances (>70%) in the San Juan for >18" of
    snow. The WSSI-P Moderate probabilities are keying in on the San
    Juans as seeing the most impactful snow from this event, primarily
    due to a combination of the algorithm's focus on snow totals,
    snowfall rates, and snow load. Probabilities are showing moderate
    chances (40-60%) for snowfall that would result in hazardous
    driving conditions and potential closures and disruptions to
    infrastructure in the San Juans, Wasatch, and Uinta. While Moderate
    Impacts are deemed lower chance (10-30%) in the Absaroka, Wind
    River, and Big Horn Ranges, potential impacts are elevated compared
    to what the algorithm suggests given it is the first significant
    winter storm of the season in these Ranges above 7,000ft. There are moderate-high chances (50-70%) for Minor Impacts in these Ranges,
    as well as far south as parts of the Sangre De Cristo and far
    northern mountains of Arizona.


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

    Mullinax



    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Oct 18 08:41:00 2024
    FOUS11 KWBC 180830
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    430 AM EDT Fri Oct 18 2024

    Valid 12Z Fri Oct 18 2024 - 12Z Mon Oct 21 2024

    ...Central and Southern Rockies...
    Days 1-2...

    Potent low closes off over northern AZ this morning where it stalls/occludes/fills through Saturday. This will result in a
    prolonged period of intense synoptic ascent focused across the Four
    Corners and southern/central Rockies, where height falls,
    downstream divergence, and upper level diffluence in response to
    modestly coupled jet streaks overlap. At the same time, a surface
    cold front will shift east over the Four Corners today and over the
    southern Rockies tonight. This will have a two-pronged effect of
    enhancing ascent, as a wave of low pressure develops along it,
    while impressive baroclinicity results in sharpening fgen to drive
    locally more intense lift. Where this most intense ascent occurs,
    especially in areas of upslope flow, precipitation rates will be
    heavy.

    Downstream of this upper low, strong moisture advection leads to
    PWs +2 to +3 sigma, additionally supporting widespread heavy
    precipitation. Snow levels ahead of the low are quite high,
    varying between 9000 to 10000ft, but will fall to around 6500ft
    underneath the upper low over AZ tonight. Day 1 PWPF for >8" is
    over 50% in the higher southern UT ranges and the Kaibab Plateau
    and around Humphreys Peak in northern AZ along with over 80% for
    12" additional in the San Juans of CO.

    The filling low causes precip rate to drop to light to moderate
    with snow levels lingering around 9000ft over the San Juans. Day 2
    PWPF for additional >8" is 30-50%.


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

    Jackson


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Oct 21 08:58:00 2024
    FOUS11 KWBC 210820
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    420 AM EDT Mon Oct 21 2024

    Valid 12Z Mon Oct 21 2024 - 12Z Thu Oct 24 2024

    ...Colorado Rockies...

    Day 1...
    An upper low centered over central CO early this morning will shift
    east into KS by early afternoon. Comma head precip, moderate at
    times, on the back side of the low will persist over the north-
    central CO Rockies through this morning with snow levels around
    9000ft. Probs for an additional >6" snow between 12Z and 18Z are
    around 50 percent in portions of the Front Range.


    ...Glacier National Park...
    Day 1...

    An upper trough axis reaches the PacNW coast early this morning and
    shift ENE through western MT this evening. An inland surge of
    Pacific moisture ahead of this trough maintains high snow levels
    over the Northwest today, but height falls are sufficient by this
    evening to allow snow levels to drop on the Lewis Range through
    Glacier NP to drop from around 7000 to 5000ft tonight. PWPF for >6"
    is around 30 percent on the higher peaks of the park.


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

    Jackson


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Oct 22 08:40:00 2024
    FOUS11 KWBC 220712
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    312 AM EDT Tue Oct 22 2024

    Valid 12Z Tue Oct 22 2024 - 12Z Fri Oct 25 2024

    ...Greater Yellowstone...
    Day 2...

    A rather positively tilted trough extending WSW from southern BC
    closed off into a mid-level low today west of WA. This low then
    opens into a compact trough and ejects east Wednesday with the H5
    trough axis crossing greater Yellowstone late Wednesday night. Snow
    levels in the moisture ahead of this wave are 8000-9000ft. The
    only snow probs for >4" in the WWD forecast period are on Day 2 and
    in the 20-40% range over the northern Absarokas in MT and for the
    Tetons. There is about a 10% risk for 6" in the Red Lodge portion
    toward Beartooth Pass.


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

    Jackson


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Wed Oct 23 08:21:00 2024
    FOUS11 KWBC 230703
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    303 AM EDT Wed Oct 23 2024

    Valid 12Z Wed Oct 23 2024 - 12Z Sat Oct 26 2024

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

    Mid-level low off the WA/OR coast opens into compact shortwave
    and ejects east over the OR Coast this afternoon before weakening
    as it reaches western WY late tonight. Lee-side low pressure
    develops over northern WY overnight which aids upslope flow back on
    the western WY terrain where snow reaches moderate rates overnight.
    Snow levels drop from around 8000ft to 7000ft overnight during this
    precip, particularly around greater Yellowstone. Day 1 PWPF are
    10-40% for >4" over the northern Absarokas in southern MT and in
    the Tetons.


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


    Jackson


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Oct 25 10:01:00 2024
    FOUS11 KWBC 250730
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    330 AM EDT Fri Oct 25 2024

    Valid 12Z Fri Oct 25 2024 - 12Z Mon Oct 28 2024


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

    Upper level ridging will give way to a broad upper trough, carved
    out by a series of shortwaves moving south of a low moving into
    British Columbia. This will support the return of unsettled weather
    and falling snow levels in the wake of a strong cold front moving
    from the Northwest into the northern Rockies on Sunday. Strong mid-
    to-upper level forcing and a shot of deeper moisture are expected
    to generate some of the heaviest precipitation across western
    Washington and Oregon Saturday night into Sunday morning. However,
    with snow levels above 6000 ft in most locations, winter weather
    impacts will be limited. Snow levels are expected to steadily drop
    through Sunday, reaching to around 4500 ft in the northern Cascades
    by Monday morning. Conditions will remain unsettled as onshore
    flow persists. However, WPC probabilities indicate that most
    significant snow accumulations will remain above pass level.

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

    Pereira

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Oct 25 15:13:00 2024
    FOUS11 KWBC 251905
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    305 PM EDT Fri Oct 25 2024

    Valid 00Z Sat Oct 26 2024 - 00Z Tue Oct 29 2024


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

    An impressive closed low spinning off the British Columbia coast
    will shed a shortwave and accompanying vorticity maxima into the
    Pacific Northwest Sunday. This feature will spread height falls and
    PVA to drive ascent eastward, with a collocated upper jet streak
    also pivoting onshore to enhance lift. The best moisture advection
    will occur downstream of this lead trough, but snow levels D2 will
    be quite high, 7000-8000 ft, so despite impressive IVT exceeding
    500 kg/m/s leading to widespread precipitation, snow will be
    confined to only the highest peaks of the Cascades and Olympics.
    However, during D3, the parent upper low shifts southward and opens
    into a still sharp upper trough, lifting onto the WA/OR coast
    Monday. While residual moisture will gradually decay through D3,
    sufficient ascent downstream of this trough combined with upslope
    ascent will drive continued moderate precipitation, with snow
    levels falling to 4500-5000 ft. This will allow snow to accumulate
    into lower elevations by the end of the forecast period, but
    most snow is still expected only above pass level.

    WPC probabilities for more than 6 inches of snow are only above
    30% in the highest peaks of the WA Cascades D2, where locally 2
    feet of snow or more is probably near the top of Mt Rainier. By D3
    snowfall becomes more widespread, with WPC probabilities for more
    than inches reaching 30-50% across much of the spine of the
    Cascades from WA to OR, and several feet of event-total snow is
    likely on the higher mountain tops.

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

    Weiss



    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Oct 26 07:26:00 2024
    FOUS11 KWBC 260845
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    445 AM EDT Sat Oct 26 2024

    Valid 12Z Sat Oct 26 2024 - 12Z Tue Oct 29 2024


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

    Upper level ridging will give way to a broad upper trough, carved out
    by a series of shortwaves moving south of a low moving into British
    Columbia. This will support the return of unsettled weather and
    falling snow levels in the wake of a strong cold front moving from
    the Northwest into the northern Rockies on Sunday. Strong mid-to-
    upper level forcing and a shot of deeper moisture are expected to
    generate some of the heaviest precipitation across western
    Washington and Oregon Saturday night into Sunday morning. However,
    with snow levels above 6000 ft in most locations, winter weather
    impacts will be limited, initially. Snow levels are expected to
    steadily drop through Sunday, dipping to around 4500-5000 ft along
    the Washington and Oregon Cascades by Monday morning. Conditions
    will remain unsettled as onshore flow persists. WPC probabilities
    indicate that most significant snow accumulations will remain above
    the major Washington and Oregon passes through Monday Morning.

    Unsettled weather will continue across the Northwest through
    Monday, with snow levels dipping further as additional shortwaves
    move through the base of the broader scale trough as its axis
    shift inland. WPC probabilities indicate that potentially
    impactful accumulations will become more likely along the Oregon
    Cascades, with probabilities for accumulations of 4 inches or more
    climbing above 50 percent in some of the passes.

    Snow will also be spreading south into the Sierra Nevada and east
    into portions portions of the northern and central Rockies Monday
    into Tuesday. The highest probabilities for significant
    accumulations through Tuesday morning center over north-central
    Idaho and southwestern Montana and northwestern Wyoming -- in and
    around Yellowstone NP. WPC guidance shows at least low
    probabilities for accumulations of 6 inches or more in the higher
    elevations of these areas.

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

    Pereira


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Oct 27 15:04:00 2024
    FOUS11 KWBC 271922
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    322 PM EDT Sun Oct 27 2024

    Valid 00Z Mon Oct 28 2024 - 00Z Thu Oct 31 2024


    ...Pacific Northwest to the central Rockies...
    Days 1-3...

    A much more active pattern is set to develop this week as a large
    trough begins to expand across the western CONUS.

    A Pacific trough will encroach on the coast D1, with the primary
    trough axis pivoting onshore by Tuesday morning. The most
    impressive vorticity impulse embedded within this trough is progged
    to surge into central CA, which will then help to amplify this
    feature as it advects east on Tuesday into the Great Basin and then
    Four Corners. Initially, this trough will remain progressive and
    positively tilted, but should deepen, and some of the guidance
    suggests a negative tilt or even closing off of the upper height
    fields late in the forecast period. Although there is, as expected,
    some uncertainty into the placement and speed of this evolution,
    500mb heights across the West feature minimal spread in the IQR
    according to DESI, so confidence is pretty high in the progression.

    As this trough surges eastward, it will drive increasingly intense
    ascent through height falls and downstream divergence, especially
    during the period of best amplification D2, and combine with a
    strengthening 250mb jet streak pivoting from CA into the central
    Rockies to force impressive deep layer ascent, especially in the
    Rockies. At the same time, moisture will become increasingly robust
    due to onshore flow of Pacific moisture streaming ahead of the
    trough axis, and pushing PWs to +1 to +2 sigma according to NAEFS
    ensemble tables. This will result in widespread and expanding
    precipitation, first in the WA/OR Cascades, but then becoming more
    robust across the central Rockies beginning Tuesday aftn.

    The challenge with this event will be how much snow will spread out
    of the higher terrain and into the High Plains Tuesday and
    Wednesday. While forcing will remain impressive, a cold front
    digging southward will begin to cool the column, while also
    providing a region of enhanced baroclinicity leading to stronger
    frontogenesis. This should result in a surface wave developing near
    UT/CO and then lifting E/NE into the Plains by Wednesday. The
    combination of fgen, this modestly strengthening surface low, and
    the southward push of the cold front should help cause snow levels
    to crash from around 8000ft early to 4500-5000 ft late. This,
    combined with periods of dynamic cooling, will result in
    significant snow accumulations in many areas.

    The other challenge with this system will occur D3 as the low
    ejects into the Plains and leaves what could be a potent comma
    head/deformation axis with precipitation to its NW. There is
    considerable model spread in the placement/timing of this feature,
    so confidence is lower, but some of the more aggressive guidance
    indicates the band will be strong enough to cause dynamical
    cooling to support of swath of snow into the Dakotas and maybe even
    MN before the end of the forecast period. Despite favorable omega
    into a subjectively deep DGZ, the weaker/less snowfall solutions
    are preferred based on consensus and ensemble means, but it will be
    worth monitoring the next few model runs to see if this stripe of
    heavier snow could materialize.

    At this time, while uncertainty still exists in both the elevations
    at which significant snow can accumulate, and the eastern footprint
    of the heavy snow axis, heavy snow is likely in a lot of the higher
    elevations. On D1, WPC probabilities for more than 6 inches are as
    high as 70-90% in the WA Cascades as a weak low pressure approaches
    the coast beneath the primary mid-level trough. By D2, more
    expansive precipitation begins in the central Rockies, and WPC
    probabilities for more than 6 inches are above 50% in the San
    Juans, Uintas, Big Horns, Wind Rivers, and around Yellowstone NP.
    By D3 precip begins to wane, but periods of moderate to heavy snow
    will persist across the higher terrain of CO and WY, and as far
    east as the Black Hills of SD where WPC probabilities are 30-70%
    for an additional 6+ inches. Storm total snow of 12-18" is likely
    in some of the highest elevations by Wednesday night.


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

    Weiss



    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Oct 28 09:18:00 2024
    FOUS11 KWBC 280750
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    350 AM EDT Mon Oct 28 2024

    Valid 12Z Mon Oct 28 2024 - 12Z Thu Oct 31 2024


    ...Western U.S....
    Days 1-3...

    An amplified upper trough moving across the western U.S. is
    forecast to produce widespread mountain snow from the Pacific
    Northwest and the Sierra Nevada to the northern and central
    Rockies. Areas of heavy accumulations are expected, especially for
    portions of the central Rockies on Tuesday.

    A well-defined shortwave moving through the base of the upper
    trough is expected to lift northeast from the Southwest through the
    central Rockies on Tuesday. In addition to strong mid-to-upper
    level forcing, upslope flow on the northwest side of an associated
    low level wave moving across Wyoming, will likely support periods
    of heavy snowfall along the favored terrain. Ranges that will be
    impacted include the Wind River, southern Absaroka, and the Big
    Horns. WPC probabilities are 50 percent or greater for
    accumulations of 8 inches or more across parts of these areas.
    Locally heavy snows are also likely in the Black Hills, with
    amounts of 6 inches or more likely, according to WPC probabilities.

    As the system lifts out of the Southwest, other areas impacted
    will include the southwestern and west-central Colorado ranges,
    including the San Juan and Elk mountains, where heavy heavy snows
    are forecast to begin tonight, with storm totals, according to WPC probabilities, likely reaching over a foot before snow diminishes
    on Wednesday. Further west, widespread mountain snows are expected
    along the Utah mountains as well, from the southern mountains to
    the Uintas, with WPC probabilities indicating that locally heavy
    amounts of 8 inches or more likely.

    In the Northwest, onshore flow along the backside of the trough,
    will continue to support unsettled weather across the region
    through today. Snow levels will remain low enough to support light accumulations along the higher Cascades passes. Snow is expected to
    diminish on Tuesday as a shortwave ridge builds ahead of the next
    approaching system. Precipitation will then return by late
    Wednesday with the arrival of a frontal band associated with a deep
    upper low dropping south from the Gulf of Alaska. This will bring
    the return of mountain snow to the Olympics and the Cascades and
    the potential for impacts across the higher Cascades passes.

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

    Pereira


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Oct 29 08:34:00 2024
    FOUS11 KWBC 290730
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    330 AM EDT Tue Oct 29 2024

    Valid 12Z Tue Oct 29 2024 - 12Z Fri Nov 01 2024


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

    Widespread mountain snow, with locally heavy amounts, is expected
    as a well-defined shortwave moving through the base of a broader-scale
    trough lifts northeast from the Southwest, crossing the central
    Rockies into the High Plains over the next 12 hours. Areas likely
    impacted will extend from the southern Utah and southwestern
    Colorado mountains to the Wyoming ranges and the Black Hills.
    Strong upward ascent afforded in part by a developing upper jet
    couplet and low-to-mid level frontogenesis, will generate moderate
    to heavy snow that will translate northeastward across the region
    today. HREF guidance indicates that locally intense bands,
    producing rates of 1-2 in/hr, can be expected to develop initially
    over the Utah and western Colorado mountains this morning before
    lifting into Wyoming, where more widespread heavy snow is likely
    to develop by the afternoon and continue into the evening. WPC
    guidance shows locally high probabilities for accumulations of 8
    inches or more along the central Utah and west-central Colorado
    ranges. More widespread coverage is shown across the central
    Wyoming ranges, including the Wind River and eastern Absaroka
    ranges, the Owl Creek Mountains, and Big Horns. WPC guidance
    suggests widespread amounts of 8 inches or more across these areas,
    with totals topping 18 inches across some of the higher terrain.
    Rain changing to snow will produce some lighter accumulations,
    generally around 1-2 inches across the northeastern Wyoming Plains.
    However, heavier accumulations of 8 inches or more can be expected
    across the higher elevations of the Black Hills.

    ...Northwest to the Northern Rockies...
    Days 2/3...

    Much of the Northwest will be dry today as a shortwave ridge
    builds and moves east across the region ahead of the next
    approaching system. This next system will be a deep low that is
    expected to rapidly develop over the Gulf of Alaska today. This
    system is forecast to drop south, with its associated frontal band
    expected to move into the Pacific Northwest on Wednesday. As the
    low reaches the Northwest on Thursday, it is forecast to turn to
    the east and move toward the northern Rockies as it gradually
    weakens. The heaviest precipitation is expected to focus across
    western Oregon and northwestern California, generated by strong
    forcing and moisture advection. Significant snow accumulations are
    likely along the Oregon passes as snow levels dip below 4500 ft. By
    Wednesday night, snow will begin to develop and spread east from
    the northeastern Oregon into the central Idaho ranges, where some
    locally heavy amounts of 6 inches or more can be expected by Friday
    morning.

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


    Pereira


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Wed Oct 30 08:01:00 2024
    FOUS11 KWBC 300830
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    430 AM EDT Wed Oct 30 2024

    Valid 12Z Wed Oct 30 2024 - 12Z Sat Nov 02 2024

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

    Snow showers will continue across portions of the central Rockies,
    as an upper trough moves across the region today. While widespread
    heavy amounts are not expected, WPC probabilities indicate that
    additional accumulations of 4 inches or more are possible across
    the higher elevations of the west-central to north-central Colorado
    mountains. Snows are expected to diminish as the upper trough moves
    east into the central Plains this evening.

    ...Northwest to the Northern Rockies...
    Days 1-3...

    Precipitation will return to the Northwest and northern California
    as a well-defined frontal band associated with a deep low dropping
    out of the Gulf of Alaska moves onshore later today. Precipitation
    rates are expected to increase later this morning and continue into
    the afternoon as the front moves across the region. Rates will
    diminish by the evening and overnight, but onshore flow will
    continue to support unsettled conditions. Snow levels are expected
    to quickly drop behind the front, supporting accumulating snow
    across many of the Cascade passes.

    The upper low is expected to support another period of organized
    heavier precipitation as it continues to drop south on Thursday.
    The heaviest precipitation is expected to center from southwestern
    Washington through western Oregon into northwestern California.
    Accumulations of a foot or more are likely for portions of the
    Oregon Cascades, where snow levels are forecast to increase but
    remain near or below 5000 ft through much of the period.

    Further to the west, this series of systems will bring snow into
    the eastern Oregon and northern Nevada mountains beginning this
    evening, and the central Idaho ranges overnight, with periods of
    snow continuing through Friday. Storm total accumulations of a foot
    or more are likely across portions of the Blue Mountains in
    northeastern Oregon and the central Idaho ranges, including parts
    of the Salmon River Mountains and the Sawtooth Range.

    As the upper low remains centered over Washington through much of
    Friday, a well-defined shortwave digging to its west will move into
    northern California late Friday into early Saturday, bringing
    heavier precipitation across northwestern California into the
    Shasta-Cascade region and the northern Sierra, where high
    elevation heavy snow accumulations can be expected.

    ...Northeastern Minnesota to Upper Michigan...
    Day 2...

    The previously noted upper trough crossing the central Rockies
    today is forecast to lift northeast through the central Plains and
    into the upper Midwest by early Thursday. Guidance shows the upper
    trough briefly assuming a negative tilt, with a closed 500 mb
    center developing as moves into the upper Midwest Thursday morning.
    As the surface, low pressure is expected to quickly deepen and
    track northeast across the upper Mississippi Valley into the Great
    Lakes. Beginning Thursday morning, models are showing rain
    changing to snow within the strong low-to-mid level frontogenesis
    band on the northwest side of the low, with some hi-res guidance
    indicating snowfall rates increasing upward of 2 in/hr from east-
    central Minnesota to the North Shore and northwestern Wisconsin.
    While warm ground temperatures and solar insolation may help to
    keep amounts in check, these rates, should they develop, will
    likely to be sufficient to produce at least a few inches in some
    locations. The overall trend in the overnight models was toward a
    colder and wetter solution. So while probabilities for anything
    above light accumulations have been low, it is expected these will
    increase should these trends persist.

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

    Pereira


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Thu Oct 31 09:13:00 2024
    FOUS11 KWBC 301932
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    332 PM EDT Wed Oct 30 2024

    Valid 00Z Thu Oct 31 2024 - 00Z Sun Nov 03 2024

    ...Northeastern Minnesota to Upper Michigan...
    Days 1-2...

    A vigorous upper level trough entering the Central Plains tonight
    will lead to a strengthening area of low pressure that tracks into
    the Upper Mississippi Valley by Thursday morning. This setup is
    driven heavily by strong synoptic-scale ascent over eastern MN,
    northern WI, and upper MI Thursday morning thanks to robust
    250-500mb upper level divergence. As the storm strengthens Thursday
    morning, dynamic cooling within the column coupled with intense
    vertical velocities just below of, and including some lower
    sections, of a saturated DGZ will support periods of heavy snow
    from east-central MN to the MN Arrowhead, northern WI, and the
    western most communities of MI's Upper Peninsula. Latest WPC
    Snowband Probability Tracker does suggest the potential for 1-2"/hr
    snowfall rates from just north of the Twin Cities metro area to
    more prominently around Duluth, its surrounding communities, and on
    north and east to include the coastal portions of the Arrowhead and
    northwest WI. This event is a fairly fast moving setup with snow
    starting mid-morning in parts of eastern MN, then concluding close
    to sunset. The start and end times across northwest WI and the MI
    Upper Peninsula would be closer to early afternoon for a start time
    and ending around midnight local time.

    Snowfall totals will likely be heavily driven by which areas reside
    beneath the deformation axis, which is still not fully agreed upon
    by guidance across the board. That said, most guidance does show an
    opportunity for heavy snow in areas that would be experiencing
    there first measurable snowfall of the season. Given that is would
    be the first snow, the potential impacts are more amplified for
    residents in these areas. The latest WSSI does show a large Minor
    Impact area that stretches from the northern Twin Cities suburbs to
    as far north as the MN Arrowhead and as far east as the western
    most section of MI's Upper Peninsula. It is northwest WI to the
    east of Duluth that show localized areas of Moderate to even Major
    Impacts. These impacts are driven largely due to a combination of
    the algorithm's Snow Amount and Snow Load components, signifying
    that this is likely to be a heavy, wet snow in areas that could
    result in detrimental impacts to trees branches and possibly power
    lines. The good news is the storm will be racing east Thursday
    night and any lingering snowfall is effectively finished around
    sunrise Friday morning.

    ...Northwest to the Northern Rockies...
    Days 1-3...

    A potent storm system is arriving in the Pacific Northwest today
    that is ushering in the next round of unsettled weather as far east
    as the Northern Rockies and northern Great Basin. Initially, a cold front
    will track through the Pacific Northwest today that begins the process
    of lowering snow levels below 4,000ft by this evening throughout much
    of the Pacific Northwest. NAEFS shows an upper level trough, sporting
    500mb and 700mb heights below the 10th climatological percentile,
    barreling into the Pacific Northwest and southern British Columbia
    early Thursday morning. This upper level feature is also directing
    a 300-400 kg/m/s IVT (above the 90th climatological percentile
    over northern CA) into portions of the Northwest. There is not much
    in the way of a sub-freezing air-mass either in front of, or in
    wake of the upper low. This should keep most heavy snow to
    elevations above 4,000ft in the Cascade Range, Siskiyou, and
    Shasta. This same stream of moisture will reach the northern
    Rockies late tonight and into Thursday where heavy snowfall
    5,000ft is expected in the Blue, Sawtooth, Boise, and Teton
    Mountains.

    The upper low lingers along the Pacific Northwest coast through
    Friday morning, then finally advances inland through the Northwest
    Friday night. A cold front will advance south through northern
    California and help to cause lowering snow levels throughout the
    northern and central Sierra Nevada on Saturday. Periods of snow are
    possible in the higher ridge lines of the northern Great Basin on
    Saturday and as far east as the Tetons and Wasatch Saturday
    afternoon.

    WPC 72-hr PWPF shows high chances (>70%) of snowfall totals >18"
    in the Oregon Cascades above 5,000ft, with some of the tallest
    peaks above 6,000ft having similar high probabilities for snowfall
    totals >30". Farther east, the Blue and Sawtooth Mountains at
    elevations above 6,000ft have moderate-to-high chances (50-70%) for
    snowfall amounts >18". Even portions of the Washington Cascades
    are forecast to see some heavy snow with moderate-to-high chances
    70%) for >12" of snowfall at elevations above 4,000ft. Farther
    south, the Sierra Nevada and Siskiyou sport moderate-to-high odds
    (50-70%) for snowfall >8" on Saturday with additional snowfall
    likely to occur Saturday night. In terms of impacts, the
    Probabilistic WSSI shows Moderate chances (40-60%) for Moderate
    Impacts along the Oregon Cascades and the southern peaks of the
    Washington Cascades. These areas can expect the more treacherous
    travel conditions, particularly where heavy snow falls around pass
    level. Elsewhere, the other mountain ranges listed sport generally low-to-moderate chances (30-50%) for Minor Impacts.


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

    Mullinax





    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Nov 1 09:26:00 2024
    FOUS11 KWBC 010623
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    223 AM EDT Fri Nov 1 2024

    Valid 12Z Fri Nov 01 2024 - 12Z Mon Nov 04 2024

    ...Mountainous West...
    Days 1-3...

    Active period in the Western CONUS over the next few days
    downstream of a very strong upper ridge (~99th percentile) between
    Alaska and Hawaii. This will help guide several northern stream
    systems into the West Coast and into the Intermountain West this
    weekend into early next week. With the source region in the mid-
    latitudes, moisture anomalies with each system will be modest and
    thus the brunt of the snowfall will be driven by orographic upslope
    into the Cascades initially then into the Rockies thereafter. Snow
    levels will be on the higher side but still low enough at times to
    bring some snow to the higher mountain passes.

    D1 system will have the largest QPF amounts, primarily into the
    WA/OR Cascades, as a cold front comes ashore. D1 probabilities of
    at least 8 inches of snow are >50% above ~5000-6000ft. Into the
    weekend, the lead system will move through the Great Basin with
    light to moderate snow across central Idaho/western Montana and
    into the Tetons southward through the Uintas and Wasatch. WPC
    probabilities for at least 8 inches of snow D2 are low (<40%) in
    these areas but a bit higher into the OR Cascades with the next
    system quickly approaching the coast. By D3, that system will slip
    through the Great Basin and into the central Rockies, with more
    moderate totals possible into northern CO (Medicine Bow). Light
    snow will work its way into the Front Range by the end of the
    period as low pressure deepens over southeastern CO. WPC
    probabilities of at least 8 inches of snow are >50% above 10,000ft
    or so and for at least 4 inches are >50% above 8000ft.

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

    Fracasso





    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Nov 2 09:32:00 2024
    FOUS11 KWBC 020637
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    237 AM EDT Sat Nov 2 2024

    Valid 12Z Sat Nov 02 2024 - 12Z Tue Nov 05 2024

    ...Mountainous West...
    Days 1-3...

    An active pattern remains for much of the West this period,
    downstream of a strong upper ridge between Alaska and Hawaii. This
    will take a series of systems on a NW to SE path from the PacNW
    through the Great Basin and into the Rockies this weekend into
    early next week. For day 1, ongoing system in the NW will continue
    to bring snow to the Cascades eastward to the northern Rockies and
    southward through the Bitterroots, Tetons, Wind River, into the
    Wasatch. WPC probabilities for at least 8 inches of snow are >50%
    above 5000ft or so in the NW to about 9000ft over the Uintas.

    On day 2, the trough will dig into the Four Corners region and
    support light to modest snow for the CO Rockies, especially above
    10,000ft where WPC probabilities for at least 8 inches of snow are
    50%. Light snow is probable into the I-25 corridor but amounts are
    quite uncertain. Accumulating snow is favored farther south into
    the Palmer Divide. By day 3, that upper trough will continue to
    move slowly through NM with a focus for snowfall over the Sangre de
    Cristos into the Raton Mesa. There, WPC probabilities for at least
    8 inches of snow are moderate (40-70%). Back to the PacNW, the
    next system will move ashore with another surge in moisture to the
    area and significant snow for the WA Cascades. Snow levels will
    rise to 4500ft or so with a decent moisture plume (300-400 kg-m/s
    IVT) then fall behind the front. Higher mountains passes will
    likely be affected with significant accumulations, but lowering
    snow levels will likely affect some lower passes as well. WPC
    probabilities for at least 8 inches of snow are >50% above
    3000-3500ft or so.


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

    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Nov 3 09:27:00 2024
    FOUS11 KWBC 030705
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    205 AM EST Sun Nov 3 2024

    Valid 12Z Sun Nov 03 2024 - 12Z Wed Nov 06 2024

    ...Mountainous West...
    Days 1-3...

    Upper troughing over the Great Basin this morning will continue to
    dig into the Four Corners region into tomorrow, promoting broad
    lift over the Wasatch and especially the CO Rockies. WPC D1
    probabilities of at least 8 inches of snow are >50% above 10,000ft
    or so.

    Into D2, upper low will be moving out of NM with lingering snow
    for the San Juans, Raton Mesa, and Jemez Mountains where WPC
    probabilities for an additional 8 inches of snow are moderate
    (40-70%). Concurrently, a shortwave out of the northeastern Pacific
    will push into Washington with a brief surge in moisture aimed at
    the WA Cascades before weakening as the cold front moves inland.
    Snow levels will rise from ~4000 to 6000ft as the core of the WAA
    surges in ahead of the front, then will fall back below 4000ft
    post-FROPA. Moisture should reach into the northern ID mountains
    and into NW MT as well, where WPC probabilities for at least 8
    inches of snow are >50% above 4000-5000ft or so.

    By D3, the system in the NW will continue toward the Rockies with
    upstream vorticity at the nose of a 140kt jet streaming in across
    the PacNW, helping to amplify the pattern over the eastern Pacific
    into western North America. This, in turn, will carve out a broad
    upper trough that will dig into the Four Corners region through the
    end of the period (and then beyond). Broad lift combined with more
    localized upslope will maximize snow over the higher terrain as
    snow levels fall to the valley floors in most areas of the Northern
    Tier. WPC probabilities for at least 8 inches of snow are highest
    70%) over the Little Belt Mountains in MT as well as the Big Snow
    Mountains due to the favorable northerly flow. Lighter snow is
    forecast for the central Idaho ranges, NW MT around Glacier NP,
    southward through western WY and into the CO Rockies.

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

    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Nov 4 08:29:00 2024
    FOUS11 KWBC 040704
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    204 AM EST Mon Nov 4 2024

    Valid 12Z Mon Nov 04 2024 - 12Z Thu Nov 07 2024

    ...CO/NM border...
    Day 1...

    Upper low over NM this morning will lift northeastward across the
    TX Panhandle this evening. Snow on the NW side of the low within a
    region of modest PVA and enhanced upslope into the Raton Mesa will
    continue for the first part of D1 before tapering off later this
    evening and overnight. Lighter snow will extend eastward into the
    far western OK Panhandle as rain changes to snow. WPC probabilities
    for at least 8 inches of snow are >50% above 9000-10,000ft over
    portions of central/northern NM and across the CO line.


    ...Northwest and Northern/Central Rockies...
    Days 1-2...

    Next system coming into the PacNW will be the last for at least a
    little bit in what has been quite a busy stretch. Warm front will
    move ashore today bringing in a surge of moisture and rising snow
    levels up to around 4000ft to the north and 6000ft to the south
    over the WA Cascades, but only rising to around 5000ft farther east
    toward the Divide. Strong and favorable upslope flow will maximize
    over the WA Cascades where a few feet of snow will be possible at
    the higher peaks. By late in the evening and overnight into
    Tuesday, snow levels will fall to around 3000ft bringing
    accumulating snow to many of the lower passes across the Cascades.
    WPC probabilities for at least 8 inches of snow are >50% above
    3500ft or so. Upper jet will continue inland and promote moderate
    snow across the northern ID ranges into northwestern Montana. Into
    D2, the mid-level vort will deepen and split, with the northern
    portion closing off along the MT/Canadian border before pivoting
    back southward Tuesday evening over central MT. This will maintain
    modest snow over the central MT terrain (i.e., Little Belt and Big
    Snowy Mountains) on upslope northerly flow. There, WPC
    probabilities for at least 8 inches of snow D2 are >50% above
    4000ft or so. The southern portion of the mid-level trough will dig
    into the Great Basin through early Wednesday, spreading snow
    across UT/CO where several inches are likely, especially into the
    CO Rockies. By the end of D2, an upper low will start to close off
    over the Four Corners region, setting up the next phase of the
    system.


    ...Four Corners...
    Day 3...

    Aforementioned upper low is forecast to be situated over eastern
    UT early Wednesday morning and will likely sink southward through
    the day to a position over eastern AZ by the end of D3. This will
    keep a relatively consistent SW to S flow over northern NM into
    southern CO, which is quite favorable for upslope enhancement over
    the San Juans and into the Sangre de Cristos among other ranges.
    Multiple waves of PVA will rotate around the upper low and across
    the region, favoring moderate to heavy snow at times with a high
    likelihood (>60% chance) of moderate impacts per the
    probabilistic WSSI. WPC probabilities for at least 8 inches of
    snow are >50% above 6000-8000ft and probabilities for at least 4
    inches >50% down to around 5000-7000ft. Colder air filtering into
    northeastern CO will also promote light to perhaps modest snow over
    the I-25 corridor with heavier totals likely into the Palmer
    Divide. Heavy snow is forecast to continue past the end of D3 as
    the system slowly moves through the region. Please see the Winter
    Weather Outlook and the Probabilistic Winter Storm Severity Index
    (WSSI-P) for more information.

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

    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Nov 5 09:30:00 2024
    FOUS11 KWBC 050721
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    221 AM EST Tue Nov 5 2024

    Valid 12Z Tue Nov 05 2024 - 12Z Fri Nov 08 2024


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

    Vigorous upper trough moving through the NW will start its
    transition to separate systems... the northern entity becoming an
    upper low that will wobble through eastern Montana later today and
    overnight. Broad divergence will favor light snow over much of
    Montana but the eastward then southward movement of the forming
    upper low will turn the flow northerly over central portions of the
    state, which will enhance upslope flow into the Little Belt, Big
    Snowy, and Big Horn Mountains. Snow will fall at a modest to heavy
    rates per the 00Z HREF which shows >1"/hr probs of 50-90%. Lighter
    snow is expected farther south through WY into CO as the southern
    portion of the trough begins to split off and sink toward the Four
    Corners, with some higher totals in the high terrain. Snowfall
    should gradually taper off in most areas by Wednesday morning
    (north) or overnight (south). WPC PWPF shows high chances (>70%)
    for snowfall totals >8" over many of the MT ranges, especially
    6,000ft, through Wednesday afternoon. Some of the tallest peaks of
    these ranges could surpass 24" locally.

    ...Four Corners...
    Day 2-3...

    The southern part of the upper level feature responsible for the
    heavy snow in the northern Rockies will sink southward through
    eastern UT on Wednesday into AZ by early Thursday. After that, it
    should slowly turn eastward into NM, but the guidance remains
    inconsistent in the evolution/track. A cold front will bring in
    colder air to the southern Rockies onto the High Plains as strong
    upper level divergence aloft will support broad ascent over the
    region. Moisture levels will be modest, but IVT on southwest to
    southerly flow is forecast to be near the 90th percentile which
    should act in concert with upslope enhancement to promote moderate
    to heavy snow over the southern Rockies. Trend has been a bit less
    and farther south with the QPF, resulting in a bit less snow for
    northern areas in CO and continued uncertainty in snow amounts over
    NM. Nevertheless, significant snow is still expected in at least
    portions of southern CO into northern NM with this dynamic system.

    The upslope component should favor both the SW/S-facing slopes of
    the San Juans and Sangre de Cristos as well as farther north into
    the Front Range via the cold front. The key on Thursday will be
    where the upper low sets up and the extent of the moisture/upslope
    flow into the Southern Rockies. By Friday morning, the upper low is
    forecast to drift into NM with the brunt of the snowfall over NM.

    WPC PWPF for the event through 12Z Fri shows high chances (>70%)
    for snowfall >8" in the San Juans, the Sangre De Cristo, and into
    parts of the far western High Plains. Highest totals are likely
    over the Sangre De Cristo where 2ft+ is possible (>50% chance).
    Around the Denver metro area, WPC PWPF for >4" of snow are around
    30% but increase to the south (i.e., Palmer Divide) and then
    increase again near/south of Colorado Springs and Pueblo to reach
    70%.


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


    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Wed Nov 6 08:40:00 2024
    FOUS11 KWBC 060807
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    307 AM EST Wed Nov 6 2024

    Valid 12Z Wed Nov 06 2024 - 12Z Sat Nov 09 2024


    ...Central/Southern Rockies and Adjacent High Plains...
    Days 1-3...

    Upper low at the base of a larger western CONUS trough lies over
    southeastern UT this morning, and will continue sinking southward
    today into AZ. It will slowly detach from the northern stream and
    cut off as it wobbles southward then eastward into southern NM by
    early Friday. Then, feeling the push of the subtropical jet, it
    will lift northeastward across the northern TX Panhandle and far
    western OK Panhandle to the CO/KS border by early Saturday. The
    slow movement of the upper low combined with a fairly steady
    stretch of moisture as well as upslope enhancement will lead to
    significant snow accumulations in parts of the NM mountains and
    across the CO line along the Sangre de Cristo range. Impacts may be
    major to extreme in some locations.

    For D1, frontal boundary over southeastern CO on the edge of the
    height falls will see modest to locally heavy snow continue this
    morning in an area of surface convergence and beneath bouts of PVA.
    Through the day, as the upper low tucks farther southwest of CO,
    heights should rise and the snow should lessen. Nevertheless,
    snowfall rates of >1"/hr should yield an additional several inches
    near/south of DEN and eastward over the High Plains. There, WPC
    probabilities for at least 8 inches of snow after 12Z are moderate
    (40-70%). Farther south over NM, closer to the stream of moisture
    and vort maxes rotating around the upper low center, snow will
    increase in intensity over much of the NM terrain where snowfall
    just on D1 will likely exceed 8 inches (probabilities >70%) in the
    terrain (e.g., Sangre de Cristos/Raton Mesa/Jemez Mnts).

    By D2, slow movement of the upper low will allow for continued
    snowfall to its east via persistent IVT values near/above the 90th
    percentile. This could result in 1-2ft of snow over the NM terrain
    (WPC probabilities for at least 12 inches are >70% over much of
    northeastern NM) along with areas of blowing/drifting snow eastward
    into the western OK Panhandle. Snow will continue over northern NM
    into southern CO along the Sangre de Cristos and onto the High
    Plains as the upper low sloshes toward the TX/OK Panhandles.
    Moisture source will add in then largely switch to the western
    Gulf, wrapping around the upper low and capitalizing on upslope
    from the northeast through the column. Snow will finally start to
    taper off by the end of the period (early Saturday).

    All told, 3-day WPC probabilities for at least 24 inches of snow
    are >50% above 6000-7000ft over the Sangre de Cristos and Raton
    Mesa, with a large footprint of at least 6 inches over much of
    eastern CO southward into central NM.


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


    Fracasso



    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Nov 9 09:03:00 2024
    FOUS11 KWBC 090736
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    236 AM EST Sat Nov 9 2024

    Valid 12Z Sat Nov 09 2024 - 12Z Tue Nov 12 2024


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

    The historic winter storm that has brought multiple feet of snow to
    many parts of the Southern Rockies and central High Plains will
    wane quickly Saturday morning as the low becomes vertically stacked
    and occludes, shutting off the primary moisture feed. Despite this
    occurring, the primary upper low will remain intense, and the
    strong deformation axis responsible for the heavy snow banding
    overnight will pivot across north-central CO into southeast WY
    before slowly eroding through the day. The thermal profile to the
    northeast is less conducive for snow, but some dynamic cooling due
    to strong ascent could still result in some modest snowfall through
    early Saturday. However, the greatest potential for any additional
    significant accumulations will be across the higher terrain of
    north-central CO, including the Park Range where WPC probabilities
    for an additional 4+ inches of snow are 50-70%.


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

    A potent upper trough digging from the Gulf of Alaska will dig
    towards Washington State, but likely come ashore over British
    Columbia Monday night. This will have a two-pronged effect of
    causing broad height falls across the Pacific and Interior
    Northwest (height anomalies -1 sigma according to NAEFS) while also
    causing some pinched broadly cyclonic flow into the Northwest
    CONUS. Together, this will drive a corridor of moderate IVT for
    which CW3E probabilities from the ECENS and GEFS suggest will
    exceed 500 kg/m/s as an AR surges onshore, accompanied by a surface
    cold front advecting eastward. This will result in a stripe of
    heavy precipitation ahead of the cold front, with a secondary wave
    of precipitation following in its wake embedded within the
    confluent mid-level flow.

    Snow levels ahead of the front will be generally 6000-7000 ft, so
    the initial precipitation should fall as primarily rain except in
    the highest terrain of the Cascades. However, as snow levels crash
    behind the front and precipitation persists, accumulating snow will
    occur as low as 3500-4000 ft by the end of the period. This will
    result in significant snowfall in the WA/OR Cascades and the
    Olympics, with increasing pass-level impacts possible.
    Additionally, by Tuesday morning /end of D3/ precipitation falling
    as snow is expected to spread as far east as the Northern Rockies
    and areas around Yellowstone NP.

    WPC probabilities for more than 4 inches of snow on D2 are confined
    to the far northern WA Cascades and the higher terrain around Mt.
    Rainier where they are above 70%. By D3, snowfall expands along the
    Cascades and as far south as the Sierra, while additionally
    pushing inland to the Northern Rockies. WPC probabilities for more
    than 6 inches D3 are above 70% along the Cascades and near Mt.
    Shasta, where 1-2 feet of snow is likely in the highest terrain.
    Elsewhere, WPC probabilities are as high as 30-50%, highest near
    the Salmon River and Sawtooth Ranges of Idaho. With snow levels
    falling, impactful pass-level snow is also likely, especially at
    some of the higher passes like Washington Pass and Stevens Pass in
    the WA Cascades.

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

    Weiss

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

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

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Nov 10 09:51:00 2024
    FOUS11 KWBC 100738
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    238 AM EST Sun Nov 10 2024

    Valid 12Z Sun Nov 10 2024 - 12Z Wed Nov 13 2024

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

    Dual amplified shortwaves will bring an active period of weather to
    the Pacific and Interior Northwest through mid-week. The first of
    these will dig out of the Gulf of Alaska and approach the British
    Columbia coast Sunday night, before sharpening into a short-
    wavelength but amplified open wave advecting onshore WA/OR Monday
    evening. This feature will then move quickly eastward into the
    Northern Rockies while weakening through Tuesday. Although this
    trough will be of modest amplitude and progressive, height falls,
    divergence and dual jet streaks (one poleward arcing downstream of
    the trough axis, another more zonally oriented upstream) will lead
    to widespread deep layer ascent from the Pacific Northwest eastward
    through the Northern Rockies. At the same time, this trough will
    drive a cold front eastward, surging onshore the WA/OR coasts
    Monday morning before racing into the Northern High Plains by the
    end of the forecast period.

    This synoptic lift will act upon an increasingly moist column noted
    by rapidly rising 1000-500mb RH as warm/moist advection occurs
    within the aforementioned jet streaks, driving IVT to 250-500
    kg/m/s. This will support widespread moderate to heavy
    precipitation, and as snow levels collapse from around 6000 ft
    early to as low as 3500 ft D2, snow will become widespread in the
    terrain of the Olympics, Cascades, Shasta/Trinity region of CA, the
    Sierra, and then into the Northern Rockies. WPC probabilities for
    at least 6 inches of snow are 70+% along the spine of the Cascades
    of WA and OR, with amounts reaching multiple feet likely in the
    highest volcanoes. There is also a 30-50% chance of more than 6
    inches in the Shasta/Trinity region, the northern Sierra, the Blue
    Mountains of OR, and the far Northern Rockies.

    After a brief period of shortwave ridging across the Pacific
    Northwest, a more pronounced impulse digs into the region during D3,
    nearly reaching the coast by the end of the period. This will be
    accompanied by more impressive moist advection with ECENS IVT
    probabilities reaching above 90% for 500 kg/m/s, with several
    members exceeding 750 kg/m/s. The accompanying WAA will surge snow
    levels back to around 5000-6000 ft along the immediate coast, but
    rise only to around 4000 ft across the Cascades. This will support
    more widespread heavy snow, with generally below climo SLRs leading
    to high snow load and greater impacts, especially across the WA
    Cascades. WPC probabilities are above 9)% in the WA Cascades,
    primarily above 5000 ft, with 1-2 feet likely in the higher
    elevations. Some pass level impacts are also expected, especially
    at Washington Pass, with lesser but still potential impacts at
    Stevens Pass.


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

    Weiss


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Nov 11 08:51:00 2024
    FOUS11 KWBC 110728
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    228 AM EST Mon Nov 11 2024

    Valid 12Z Mon Nov 11 2024 - 12Z Thu Nov 14 2024

    ...Western U.S...
    Days 1-3...

    Two distinct and anomalous shortwaves will amplify and move
    progressive across the Western CONUS through Thursday, bringing an
    extended period of unsettled weather to the region, with several
    days of moderate to heavy snow expected in the higher terrain.

    The first of these will approach the Pacific Coast Monday morning,
    with downstream SW flow driving robust IVT approaching 500 kg/m/s
    onshore into CA/OR/WA. This IVT will help surge PWs to above climo
    directly ahead of a surface cold front which will be positioned
    beneath the trough axis. As this trough/front advect onshore Monday
    aftn, the overlapping ascent into the moistening column will result
    in heavy precipitation spreading from central CA through the WA
    Cascades, and then pushing east, while weakening due to lessening
    IVT, reaching the Northern Rockies and eastern Great Basin by
    Tuesday morning. Snow levels ahead of this front will be generally
    around 6000 ft during the period of heaviest precipitation, but
    will fall quickly to as low as 3500 ft behind the front. At the
    same time, while the primary forcing mechanisms will shift east,
    continued onshore moist advection in pinched mid-level flow will
    drive persistent moisture onshore, resulting in snow accumulations
    lowering across the Cascades/Olympics. WPC probabilities D1 for
    more than 6 inches of snow are above 70% along the spine of the
    Cascades in OR and WA, with up to 2 feet possible in the highest
    terrain. Lower probabilities exist into the Shasta/Trinity region,
    the northern Sierra, and as far east as the Blue Mountains of OR.

    During D2 /Tuesday and Tuesday night/ the lead trough and
    accompanying cold front continue to push east as far as the Central
    Plains while weakening, while shortwave ridging briefly builds in
    across the Northwest. This suggests that much of D2 will feature
    waning snowfall with lesser accumulations. However, before D2 ends,
    the subsequent trough will approach the Pacific Northwest once
    again. This trough is progged to be deeper, noted by 700-500mb
    height anomalies reaching -2 sigma according to NAEFS, with the
    subsequent downstream warm/moist advection in the mid and upper
    levels driving IVT to as high as 750 kg/m/s, and ECENS
    probabilities suggest even a 30% chance of IVT exceeding that
    value. This WAA will occur within a narrow channel ahead of yet
    another cold front, driving a corridor of heavy precipitation in
    conjunction with snow levels rising once again to 6000-7000 ft.
    This will limit snowfall before D2 ends except in the highest
    terrain of the Olympics and Cascades.

    The trough axis responsible for pushing the front eastward and
    driving the pronounced deep layer ascent across the Northwest will
    struggle to move east as repeated lobes of vorticity rotate down
    from the Gulf of Alaska, resulting in little movement of the trough
    axis and persistent, although weaker, moist advection onshore. This
    suggests that snow levels will only slowly fall, progged to drop
    to 4500-5000 ft by the end of the forecast period, with primarily
    light to moderate precipitation rates from northern CA through the
    Northern Rockies. This will still result in heavy snow
    accumulations at the highest elevations, reflected by WPC
    probabilities for more than 6 inches exceeding 90% in the northern
    WA Cascades, and then expanding east into Selkirk Range, the Blue
    Mountains, and the Sawtooth/Salmon River area. The higher passes
    above 5000 ft will also likely experience significant impacts from
    snow accumulations, but in general most of the passes should be
    below the heavier snow accumulation levels.


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


    Weiss


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Nov 12 10:03:00 2024
    FOUS11 KWBC 120820
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    320 AM EST Tue Nov 12 2024

    Valid 12Z Tue Nov 12 2024 - 12Z Fri Nov 15 2024

    ...Western U.S...
    Days 1-3...

    An active period of winter weather continues across the Western
    CONUS this period as dual shortwave trough cross the region.,

    The first of these will be moving from the eastern Great Basin this
    morning into the Central Plains by Wednesday evening, with minimal
    amplitude gain. The combination of the progressive nature of this
    feature with modest PW surge (at least until the Plains when
    thermals support only rain) will somewhat limit snowfall potential
    D1. However, sharp height falls downstream of the short-wavelength
    trough combined with low-level convergence along the accompanying
    cold front and post-frontal upslope flow into terrain features will
    still support rounds of moderate to heavy snow. The greatest
    potential for significant accumulations will be across the Wasatch
    and Colorado Rockies, including the Park Range, where WPC
    probabilities for more than 6 inches are above 70%, and locally up
    to 10 inches is possible, primarily above 5500 ft.

    Brief shortwave ridging blossoms across the Northwest behind this
    first trough, but is quickly replaced by a more impressive impulse
    digging along the Pacific Coast as it drops from the Gulf of
    Alaska. Downstream divergence and accompanying WAA/moist advection
    will begin to spread precipitation back into the Pacific Northwest
    late tonight. Unlike its predecessor, this secondary trough will be
    very slow to move east as it gets repeatedly reinforced just off
    the coast by renewed lobes of vorticity swinging cyclonically
    around it. This will have the two-pronged effect of driving waves
    of ascent and persistent moisture onshore, while also keeping the
    primary trough axis positioned just west of the region until Friday
    when a more pronounced vort max swings through the base and pushes
    the trough onshore CA late in the forecast period.

    Within the most impressive WAA, a narrow channel of IVT exceeding
    750 kg/m/s is likely, focused into the WA/OR and northern CA coast
    late D2 into D2 before weakening with inland extent. This channel
    /AR/ will also provide the highest increase in snow levels,
    reaching as high as 7000 ft. However, dual cold front progged to
    push onshore, one Wednesday morning and another Thursday morning,
    driven east by periodic shortwaves, will cause gradual lowering of
    snow levels to as low as 3000 ft by Friday morning across the
    Cascades, and 4500 ft into the Interior Northwest and northern CA.
    The lower snow levels will be accompanied by weaker forcing and
    more transient moisture however, so heavy pass-level snow is still
    not anticipated at this time.

    Despite that, heavy snow accumulations are likely, especially on D2
    when WPC probabilities for more than 6 inches spike above 90% in
    the Cascades, Shasta/Trinity region, the Okanogan Highlands,
    Selkirk Mountains, and Blue Mountains. Some of these areas could
    receive as much as 2 feet of snow D2, and 6-12 inches is possible
    at some of the elevated passes including Washington Pass. By D3,
    the snow intensity wanes across most of the NW, but an increase in
    WPC probabilities for 6+ inches reaching 30-50% in the Sierra as
    the trough finally pushes onshore into CA.

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


    Weiss

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Wed Nov 13 08:52:00 2024
    FOUS11 KWBC 130751
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    251 AM EST Wed Nov 13 2024

    Valid 12Z Wed Nov 13 2024 - 12Z Sat Nov 16 2024

    ...Western U.S...
    Days 1-3...

    The weather pattern over the next few days will be driven largely
    by a longwave upper level trough with a pair of upper level
    disturbances tracking into the West Coast. The first storm system
    is already impacting the Pacific Northwest with an IVT up to 750
    kg/m/s (topping the 97.5 climatological percentile) escorting
    anomalous moisture as far south as northern California and as far
    east as the Lewis Range in Montana. Elevations above 5,000ft,
    whether it be in the Cascades, Olympics, northern Sierra Nevada, or
    inland through the Blue, Sawtooth, Bitterroots, and Lewis Range,
    will be favored for witnessing accumulating snowfall that could
    result in treacherous travel conditions. The WSSI does depict some
    localized areas of Minor to Moderate Impacts in the >5,000ft
    elevations of the Olympics, Cascades, Blue, and Shasta Mountains
    today.

    Onshore flow into the Pacific Northwest will keep high elevation
    snow in the forecast through Thursday in the Northwest. By
    Thursday night, the next Pacific storm system will track farther
    south into California with 500mb heights that below the 2.5
    climatological percentile on NAEFS. Heights will be low enough
    Thursday night and into Friday morning that snow levels in the
    Sierra Nevada will be as low as 4,000ft (5,000ft in the San Gabriel
    and San Bernadino of southern California). The heaviest snowfall
    will be observed above 6,000ft in the central Sierra Nevada. WPC
    PWPF shows moderate-to-high chances (50-70%) for snowfall totals
    4" in the central Sierra Nevada between Thursday evening and
    Friday morning. By Friday afternoon, the upper trough will track
    into the heart of the Intermountain West with strong upper level
    ascent over the Northern Rockies. WPC PWPF shows moderate chances
    (40-60%) for snowfall totals >4" in the >7,000ft ranges of the
    Absaroka.

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

    An inverted trough revolving around the northern flank of a
    retrograding storm system in the northwest Atlantic will direct a
    plume of low level moisture back towards northern New England on
    Friday. The air-mass over northern New England (particularly
    Maine) will be sufficiently cold and dry enough for wet-bulb
    temperatures to remain below freezing within the boundary layer.
    Strong easterly mid-level flow with air-mass origins over the
    Atlantic will lead to warm air-advection that causes a >0C nose
    between 850-750mb Friday morning. This is a setup that will likely
    result in periods of sleet/freezing rain over northern Maine and
    possibly as far west as northern New Hampshire. WPC PWPF does show
    low chances (10-30%) for ice accumulations >0.1" in parts of the
    North Woods and Central Highlands of northern Maine. One notable
    location with those potential ice accumulations includes Baxter
    State Park. These icy conditions could result in Minor Impacts
    according to the Probabilistic WSSI with low-moderate chances
    (30-50%) through Friday afternoon. The primary impacts would be icy
    roads in some areas that could lead to slick travel conditions.

    Mullinax


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Thu Nov 14 09:27:00 2024
    FOUS11 KWBC 140802
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    302 AM EST Thu Nov 14 2024

    Valid 12Z Thu Nov 14 2024 - 12Z Sun Nov 17 2024

    ...Western U.S....
    Days 1-3...

    A pair of Pacific storm systems will produce heavy mountain snow
    from the West Coast to the Northern Rockies over the next few days.
    Today, broad scale upper level ascent out ahead of a longwave
    trough off the West Coast will also direct Pacific moisture at the
    Northwest and northern California. Periods of snow will occur for
    many of the Northwest U.S. mountain ranges which include (but are
    not limited to) the Cascades, Siskiyou, northern Sierra Nevada,
    Blue, Sawtooth, Bitterroots, Idaho Panhandle, and northern Montana
    Mountains). As a potent upper level trough approaches California
    Thursday night (500mb heights below the 2.5 climatological
    percentile via NAEFS), snow levels will fall to as low as 4,000ft
    in the Sierra Nevada and as low as 6,000ft in the San Gabriel and
    San Bernadino of southern California. The heaviest snowfall will
    be mainly confined to elevations at/above 6,000ft in the Sierra
    Nevada. By Friday morning, the upper level trough will advance
    through the Great Basin and into the Rockies by Friday afternoon.
    Periods of snow will move through northern Nevada and into the
    northern Rockies with the Tetons, Wind River, and Absaroka ranges
    seeing the heaviest snowfall Friday evening. Snow will also pick up
    in intensity along the Wasatch, Uinta, and Big Horn ranges Friday
    night and into Saturday morning. WPC PWPF shows moderate-high
    chances (50-70%) for >4" of snowfall along the Sierra Nevada above
    6,000ft, the northern Great Basin above 7,000ft, and the Absaroka,
    Tetons, and Wind River ranges above 8,000ft.

    Meanwhile, the Pacific Northwest will see periods of snow gradually
    diminish throughout the day today with a fairly tranquil day
    weather-wise on tap for Friday. By Saturday, the next Pacific
    trough approaches with a stronger IVT (>500 kg/m/s, or above the
    90th climatological percentile via NAEFS) will direct another plume
    of Pacific moisture at the region. Strong synoptic-scale support
    will also be present as 200-500mb winds over western Washington top
    the 90th climatological percentile. As the warm front arrives
    Saturday night, snow levels will rise to as high as 5,500ft in some
    cases, but once the cold front pushes through on Sunday, snow
    levels will crash and result in precipitation changing over to
    heavy snow Sunday afternoon in the Olympics and Cascades. Through
    12Z Sunday, the northern Cascades and the Idaho Panhandle above
    5,000ft sport high chances (>70%) for snowfall >6" with a low
    chance (10-30%) for >12" in the tallest peaks of the northern
    Washington Cascades.

    ...Northern Maine...
    Days 1-2...

    An inverted trough revolving around the northern flank of a
    retrograding storm system in the northwest Atlantic will direct a
    stream of low-level moisture back west towards northern New England
    late Thursday night into Friday. The air-mass over northern New
    England (particularly Maine) will be sufficiently cold and dry
    enough for wet-bulb temperatures within the boundary layer to
    remain below freezing for at least a few hours. Strong easterly
    mid-level flow with air-mass origins over the Atlantic will lead to
    warm-air advection (WAA) that causes a >0C nose between 850-750mb
    Friday morning. This setup will result in periods of sleet/freezing
    rain over northern Maine and possibly into far northern New
    Hampshire. WPC PWPF does depict some spotty areas with low chances
    (10-30%) for ice accumulations >0.1" in portions of the North Woods
    and Central Highlands of northern Maine. One notable location with
    those potential ice accumulations includes Baxter State Park. These
    icy conditions could result in Minor Impacts according to the
    Probabilistic WSSI with low chances (10-30%) through Friday
    afternoon. The primary impacts would be icy roads in some areas
    that could lead to slick travel conditions.

    Mullinax



    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Nov 15 08:58:00 2024
    FOUS11 KWBC 150811
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    311 AM EST Fri Nov 15 2024

    Valid 12Z Fri Nov 15 2024 - 12Z Mon Nov 18 2024

    ...Western U.S....
    Days 1-3...

    This morning, an upper level trough will advance through the Great
    Basin and into the Rockies by this evening. Periods of snow
    along the Sierra Nevada and northern Great Basin this morning will
    move into the northern Rockies tonight with the Tetons, Wind
    River, and Absaroka ranges seeing the heaviest snowfall. Snow will
    also pick up in intensity along the Wasatch, Uinta, Big Horn,
    Little Belt, and Big Snowy ranges tonight and into Saturday
    morning. WPC PWPF shows moderate chances (40-60%) for >6" of
    snowfall along the Sierra Nevada above 9,000ft. High probabilities
    70%) for snowfall >8" are forecast along the ridgelines of the
    northern Great Basin above 6,000ft and the Absaroka, Tetons, and
    Little Belt, and Big Snowy ranges above 7,000ft.

    Elsewhere, the Pacific Northwest will witness a fairly tranquil
    day weather-wise today. This changes by Saturday as the next
    Pacific trough approaches with a stronger IVT (>500 kg/m/s, or
    above the 90th climatological percentile via NAEFS) will direct
    another plume of Pacific moisture at the region. Strong synoptic-
    scale support will also be present as 200-500mb winds over western
    Washington top the 90th climatological percentile. As the warm
    front arrives Saturday night, snow levels will rise to as high as
    5,500ft, but once the cold front pushes through on Sunday, snow
    levels will crash and result in precipitation changing over to
    heavy snow Sunday afternoon in the Olympics and Cascades. Heavy
    snow will continue to push inland through the interior Northwest
    Sunday night while persistent upslope flow leads to a prolonged
    stretch of accumulating snowfall above 3,000ft in the Cascades.

    Through this weekend, the northern Cascades and the Idaho
    Panhandle above 5,000ft sport high chances (>70%) for snowfall >12"
    with low-moderate chances (30-50%) for >18" in the tallest peaks.
    In the Oregon Cascades and Blue Mountains, WPC PWPF shows
    moderate-high chances for >12" of snowfall. WSSI-P depicts
    moderate-high chances (50-70%) for Major Impacts in the WA/OR
    Cascades above 4,000ft, which includes some notable passes such as
    Snoqualmie Pass.

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

    Some light ice accumulations are expected across portions of
    northern Maine this morning. Warm air at mid levels overrunning
    sub-freezing low level temperatures will support periods of
    freezing rain/drizzle, especially from the St. John Valley on south
    through the Southern Aroostook. The primary impacts would be icy
    roads in some areas that could lead to slick travel conditions. WPC
    PWPF shows low-moderate chances for ice accumulations >0.01"
    through this afternoon.


    Mullinax


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Nov 16 12:24:00 2024
    FOUS11 KWBC 160820
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    320 AM EST Sat Nov 16 2024

    Valid 12Z Sat Nov 16 2024 - 12Z Tue Nov 19 2024

    ...Western U.S....
    Days 1-3...

    As one storm system originally over the Intermountain West last
    night departs (leaving some light-moderate mountain snow over parts
    of the central Rockies in its wake this morning), attention shifts
    to the next Pacific storm system that is set to bring an onslaught
    of heavy snow to the Pacific Northwest and Northern Rockies this
    weekend and into early next week. Precipitation will arrive
    Saturday morning as a warm front approaches from the West. Snow
    levels start out around 3,000ft Saturday morning, but strong warm
    air advection associated with the warm front will cause snow levels
    to rise above 7,000ft in the OR Cascades, while they are more
    focused around 5,000ft in the northern WA Cascades Saturday night.
    This same moisture plume, which is associated with a >500 kg/m/s
    IVT that also happens to be above the 90th climatological
    percentile according to NAEFS, will advect rich low-mid level
    moisture well inland into the northern Rockies Saturday night. By
    Sunday, while moisture advection into the Cascades will not be as
    strong, a cold front passing through on Sunday will cause snow
    levels to plummet to as low as 2,000ft in the WA Cascades and
    2,500ft in the Oregon Cascades by Sunday evening.

    These falling snow levels will also occur inland across the
    Northern Rockies Sunday night and into Monday. NAEFS by 00Z Monday
    shows 500mb heights that are below the 10th climatological
    percentile throughout the northwestern U.S.. By Monday afternoon,
    700mb temperatures are unusually cold across the Pacific NW with
    temps as cold as the 2.5 climatological percentile. This unusually
    cold air-mass is in place at the same time as steady onshore flow
    perpendicular to the Cascades and northern Rockies continues to
    support moderate-heavy snow from the Olympics, Cascades, and
    northern Rockies to as far south as the Salmon Mountains of
    northern California. Heavy snow not only looks to continue through
    Monday night in the Cascades and Olympics, but a much stronger
    Pacific storm system arrives on Tuesday with more heavy snow and
    much stronger winds.

    Through 12Z Tuesday, WPC PWPF shows which chances (>70%) for
    snowfall >18" in the Oregon Cascades, the northern Bitterroots of
    the Idaho Panhandle, and the tallest peaks of the Lewis Range. The
    northern Washington Cascades show high chances (>70%) for over 2
    feet of snowfall with some of the tallest peaks above 7,000ft
    topping 3 feet. Impacts will be the worst in these aforementioned
    areas with Moderate to Major Impacts shown on the WSSI, which
    includes some of the notable passes in the OR/WA Cascades.
    Elsewhere, WPC PWPF shows high chances (>70%) for >12" of snowfall
    in the Blue, Boise, and Sawtooth Mountains. Similar high chance
    probabilities exist in the Tetons for >8" of snowfall. The WSSI
    shows Minor to localized Moderate Impacts in these mountain ranges.

    ...Eastern MT & Western ND...
    Day 1...

    Over the past 24 hours, guidance shows the upper level trough
    tracking through southern Montana tonight to be more potent and
    compact than originally shown. The region remains beneath the
    divergent left-exit region of a 250mb jet streak located over the
    Four Corners region. As the 700mb low tracks through eastern
    Montana this morning, a ribbon of anomalous 700mb moisture aloft
    will wrap around the northern and western flank of the low while
    strong vertical velocities aloft and dynamic cooling allow for
    heavy snow to ensue over northeast Montana. Latest CAMs show
    excellent upward vertical velocities within a highly saturated DGZ
    around 600-550mb. The 00Z HREF Snowband Probability Tracker (SPT)
    does show a swath of snowfall rates that could hover around 2"/hr,
    if not higher in some cases. Residents in these areas can expect
    rapidly accumulating snowfall this morning with US Routes 2 and 85
    to the north and west of Williston likely to feature treacherous
    travel conditions. Slick roads and significantly reduced
    visibilities are expected where the heaviest snowfall occurs. By
    this afternoon, the storm system will be over eastern North Dakota
    and tracking to the northeast. Periods of snow will continue across
    western North Dakota before finally concluding Saturday evening.


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

    Mullinax

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Nov 17 12:23:00 2024
    FOUS11 KWBC 170812
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    312 AM EST Sun Nov 17 2024

    Valid 12Z Sun Nov 17 2024 - 12Z Wed Nov 20 2024

    ...Western U.S....
    Days 1-3...

    A developing active pattern is in its early stages as the first in
    a series of Pacific storm systems revolves beneath the base of a
    longwave trough that will become quasi-stationary in the Gulf of
    Alaska to start the period. Then, as a strong ridge builds over the
    Aleutians mid-week, the longwave trough will dive south into the
    northeast Pacific and direct a steady barrage of rich Pacific
    moisture at the region into the second half of the week. Tonight,
    the warm front associated with the initial surge in Pacific
    moisture is working across the interior Northwest. Meanwhile, a
    cold front will push across western WA/OR Sunday morning that will
    cause snow levels to plummet to as low as 2,000ft in the WA
    Cascades and 2,500ft in the OR Cascades by this afternoon. By
    Sunday evening, some locations on the windward side of the Cascades
    could see snow levels as low as 1,000ft. It is also worth noting
    that there are likely to be some instances of freezing rain today
    with low-moderate probabilities for >0.01" of freezing rain in
    parts of eastern OR and the northern ID Panhandle.

    The falling snow levels will occur well inland across the Northern
    Rockies Sunday night and into Monday. NAEFS shows 500-700mb temps
    and heights that are below the 10th percentile throughout the
    Northwest on Monday. This unusually cold air-mass is in place at
    the same time as persistent onshore flow, courtesy of the longwave
    trough to the north, strikes mountain ranges such as the Cascades
    at an orthogonal angle to maximize the snowfall potential through
    Monday. Following a brief lull Monday night, a rapidly
    strengthening storm system (both the GFS and ECMWF have the low sub
    950mb by Tuesday afternoon!) will direct a stronger atmospheric
    river at the Pacific Northwest with not only exceptional moisture
    advection (>750 kg/m/s IVT on NAEFS would be above the 97.5
    climatological percentile Tuesday afternoon), but intense winds
    along the mountainous terrain. Robust warm air-advection late
    Tuesday and into Tuesday night will lead to snow levels rising to
    above 3,000ft in the WA Cascades and Olympics, around 4,000ft in
    the OR Cascades, and 6,000ft in the northern California ranges by
    Wednesday morning. The concern would be for the potential for a
    heavier/wet snow type to rapidly accumulate, while powerful wind
    gusts potential lead to tree damage and power outages Tuesday
    night and into Wednesday.

    All told, there is no shortage of snow in the forecast for the
    Pacific Northwest and Northern Rockies. Snow is likely to be
    measured in feet along not just the Cascades above 3,000ft, but the
    Olympics, the Salmon/Shasta/Siskiyou of northern California, and
    well inland through the Blue, Sawtooth, Boise, Bitterroot, Tetons,
    and Lewis Mountain Ranges. The latest WSSI shows Moderate to Major
    Impacts in the Cascades and Bitterroots with impacts including not
    just dangerous travel conditions (including notable Cascade
    passes), but the weight of the snow and strong winds by Tuesday
    night could result in tree damage and power outages in some areas.

    ...Northern Plains...
    Day 3...

    Confidence is increasing in a powerful late November cyclone to
    track from the Southern Plains on Monday and race north into the
    Midwest Monday night. Both NAEFS and ECMWF SATs support a highly
    anomalous area of low pressure Monday night, but the ECMWF is
    farther west and closer to the Missouri River than the NAEFS, which
    is located farther east over central Iowa. By Tuesday morning, the
    NAEFS (a GFS/CMC ensemble based tool) shows the storm about to
    cross the Mississippi River in southeast MN while the ECMWF is over
    southwest MN. The primary reason for this is the ECMWF shows a
    slightly slower and stronger 500mb solution than the GFS, albeit
    they are not overly different in the storm evolution.

    Where they differ is that the ECMWF (RGEM as well) phases sooner
    with an upper level disturbance over the northern High Plains and
    is pulled farther west than the GFS. By 21Z Tuesday, both the ECMWF
    and RGEM show a closed 500mb low near Bismarck, while the GFS is
    more elongated and does not close off fully until a few hours later
    near the ND/Canada border. These details are critical in
    determining where the deformation zone (or heaviest snow bands) set
    up; over the Dakotas or more over south-central Canada. For the
    moment, WPC PWPF shows moderate-high probabilities (50-70%) for
    4" of snowfall over north-central ND. It is worth noting that the
    WPC PWPF does show low chances (10-30%) for snowfall >8", and near
    the North Dakota/Canada border, a small 10% chance area for >12" of
    snowfall. Residents in the Dakotas should monitor the forecast
    closely over the next 24-48 hours.

    While exact amounts are unclear, the exceptionally strong storm
    system over Minnesota coupled with high pressure building in over
    the Northern Rockies will make for a very windy setup over the
    Northern Plains. Snow is still expected to fall across much of
    central and western North Dakota and wind gusts of 30-40 mph would
    result in whiteout conditions for areas that, in some cases, would
    experience their first round of accumulating snowfall this season.
    The Probabilistic WSSI (WSSI-P) shows moderate-high chances
    (50-70%) for Minor Impacts across much of central North Dakota with
    the highest probabilities focused in north-central North Dakota.
    The WSSI-P shows Snow Amount and Blowing Snow to be the primary
    impacts in these areas. In summary, while exact amounts remain low
    confidence at this range, the combination of some accumulating snow
    and hazardous visibility reductions due to blowing snow are still
    likely to cause some treacherous travel conditions in these areas
    late Tuesday and into Wednesday morning.


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

    Mullinax
    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Nov 22 09:25:00 2024
    FOUS11 KWBC 220831
    QPFHSD

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

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

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

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

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

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

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

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

    The Central Appalachians, especially from the Laurel Highlands
    southward across WV and as far south as the Great Smokey Mtns of
    TN/NC, will benefit from prolonged upslope flow on the western
    periphery of the upper low resulting in waves of heavy snowfall
    through Saturday. WPC's snowband probability tracker depicts an
    extended period of 1-2"/hr snowfall rates during the D1 period
    across the Allegheny Mtns. WPC probabilities in this area are high
    70%) on D1 for more than 8 inches of snow. Event total snowfall
    could peak around 2 feet in central WV.

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

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

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

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

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

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

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

    Snell

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

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

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Nov 23 10:55:00 2024
    FOUS11 KWBC 230755
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    255 AM EST Sat Nov 23 2024

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

    ...Pacific Coast through the Intermountain West and Rockies... Days 1-3...

    Strong upper low off the Pacific Northwest finally begins to
    unravel while ejecting shortwaves inland across the West, with
    persistent onshore flow and lowering snow levels leading to
    widespread heavy mountain snowfall.

    The first shortwave ejecting through the base of an anomalous
    trough off the Pacific Coast will swing eastward into the Northwest
    Saturday and then begin to amplify into a potent but fast-moving
    impulse across the Northern Rockies and into the Northern Plains
    Sunday. This deepening system will drive downstream ascent through
    height falls, PVA, and divergence. At the same time, a zonally-
    oriented jet streak will pivot south of the region, placing its
    favorable LFQ atop the far northern High Plains and southern Canada, interacting with increasing baroclinicity as a front wavers near
    the international border. The overlap of synoptic lift with the
    enhanced mesoscale ascent through fgen will result in weak
    cyclogenesis, leading to an expanding area of precipitation falling
    as snow. The column will be plenty cold for wintry precipitation
    thanks to high pressure from Canada extending southward. As the WAA
    along the warm front lifts north, an exceptionally deep DGZ will
    support fluffy aggregate dendrites which should accumulate
    efficiently, but the most favorable environment and most impactful
    snowfall will likely be just north of the U.S.-Canada border. The
    greatest impacts over the U.S. from this system appear to occur
    over the northern Rockies on D1, where upslope flow will enhance
    ascent. WPC probabilities for at least 8 inches of snow are high
    (<70%) across northwest MT and Glacier NP, as well as the Salmon
    River and Clearwater Mts of Idaho.

    The Pacific mountain ranges spanning from the Cascades to the
    Sierra Nevada will see a few separate shortwaves move inland
    before the parent upper low finally pushes eastward on D3. The
    ongoing AR over central CA will come to an end by the start of D1
    and allow for snow levels to fall back to around 4000-5000 ft
    across the Sierra and lower (2500-3000 feet) across the Cascades.
    However, IVT values will also become very weak along the West Coast
    until a resurgence across the Sierra on D3 in response to the
    parent upper lows eastward movement. A few locally enhanced axes
    of moisture are also possible across the Pac NW D2-D3 due to the
    lingering low off the coast. This results in high probabilities
    70%) for at least a foot of total snowfall over the next three
    days across the Sierra Nevada, Shasta Siskiyous of northern
    California, Oregon Cascades, and Olympic Mts. Areas above 5000 feet
    can expect the potential for up to two feet of snow.

    Leftover moisture spilling across the Intermountain West and
    central Rockies could combine with favorable west-east upslope
    enhancement over the Wasatch Mts of Utah and Colorado ranges on D2.
    WPC probabilities for at least 8 inches of snow are low (10-30%).

    ...Northern New England... Days 1-2...

    Stacked/wrapped upper and sfc low over the Northeast will complete its counterclockwise loop this morning before a separate sfc low
    develops and lifts north through Atlantic Canada along with the
    larger upper low this weekend. Upslope snow into the central
    Appalachians will persist through this evening via NW flow as
    moisture has circulated from the Atlantic up and around
    southeastern Canada back across the lower Great Lakes. A few
    additional inches of snow are possible in elevations above 3000 ft
    in West Virginia, with marginal surface temperatures limiting the
    potential for heavier amounts.

    Into New England, trailing vorticity lobe will aid this new coastal
    sfc low east of Cape Cod that will track northward into Nova
    Scotia by tonight, favoring increased northerly/cooler flow over
    interior portions of Maine southwestward into VT. The column is
    fairly mild to start over New England via SE flow ahead of the
    initial front, but that will change on D1 with rain changing to
    snow as the low approaches and deepens. QPF will be focused closer
    to the coast, but light amounts of snow are likely for the interior
    and especially the higher terrain above 2500ft or so (White
    Mountains and northern ME) where WPC probabilities of at least 4
    inches are >40%.

    Additionally, lake effect snow showers are possible downwind of
    Lake Ontario D1-D2 due to this persistent west-northwest flow
    around the large low pressure system to the east. Warm boundary
    layer temperatures will limit snowfall accumulations as upper
    ridging quickly builds from the west. In, fact most showers may
    simply fall as rain outside the higher elevations of Upstate New
    York or within some of the locally heavier bands where dynamic
    cooling can lower surface temperatures to near freezing.

    ...Upper Great Lakes... Day 3...

    The fast-moving shortwave exiting the northern Plains on Sunday is
    forecast to reach the Upper Great Lakes on Monday while also
    taking on a negative tilt in response to a piece of upper energy
    quickly rounding the southern end of the trough over the Midwest.
    Surface low is expected to then deepen over the Great Lakes by the
    end of D3 with upper diffluence and lake enhancement off Lake
    Superior supporting periods of light to moderate snow over the
    U.P. of Michigan. WPC probabilities for at least 4 inches of snow
    are low (10-30%) for most of this region on D3, with medium
    chances (40-60%) over the Porcupine Mts.

    Snell
    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Nov 24 09:57:00 2024
    FOUS11 KWBC 240835
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    335 AM EST Sun Nov 24 2024

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

    ...Northern New England...
    Days 1-2...

    Upper low moving over Atlantic Canada is expected to stall today
    and absorb approaching upper shortwave diving southeastward over
    Ontario. These features combined with strong northwest flow will
    support upslope snow over the higher terrain of far northern New
    England (mainly the White Mts through northern Maine). WPC
    probabilities of an additional 4 inches of additional snow are
    medium (40-70%) over these areas. Light snow is also favored over
    eastern NY (Adirondacks into the Catskills) but amounts should be
    under 4 inches.

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

    Tonight, energy from two separate disturbances, one an upper level
    low over the Canadian prairies, and the other an ejecting
    shortwave out of central Great Basin, will merge over a strong
    surface cold front diving southward over the central Plains. An
    area of low pressure will then form and progress northeastward from
    the Midwest to the Great Lakes on D2. The combination of upper
    level energy and upper diffluence beneath the favorable left- exit
    region of a quick moving 250 mb 105 kt jet streak will aid in a
    blossoming precipitation shield from northern MN to northern WI and
    the U.P. of Michigan into Monday morning. As the low tracks
    northeast across the L.P., much colder air wrapping around the back
    side of the low will allow for additional widespread lake-effect
    snow and snow showers persisting into D3 for much of the U.P. WPC
    probabilities for at least 4" of snow are medium (30-60%) across
    the Arrowhead of MN, far northern WI, and the U.P. of Michigan.

    As this low and precipitation moves eastward over the Northeast
    and New England on D3, light freezing rain is possible over
    interior New England as low- level cold air remains locked in
    place as mid- level temperatures rapidly warm above freezing along
    with the precipitation shield. Surface temperatures should also
    eventually rise above freezing given the strong low forecast to
    track north of the region into southern Quebec. Only the northern
    White Mts and far northern Maine could see temperatures remain
    around the freezing mark and the entire column potentially
    remaining cold enough for light snow.

    ...Sierra, Wasatch, CO Rockies...
    Days 1-3...

    Ejecting upper shortwave and surface cold front crossing the
    Intermountain West and central Rockies today will include residual
    moisture from the atmospheric river impacting northern California
    over the last few days and will have the potential to produce a
    burst of snow over the region. Snow levels starting around
    5000-6000ft will fall below 4500-5000ft by the end of D1 and
    behind the cold front, but also as the column gradually dries out.
    WPC probabilities for at least 6 inches of snow are mostly low
    (10-30%) for the Wasatch Mts and CO Rockies, with higher chances
    above 9000ft.

    Troughing off the West Coast will continue during the short range
    period, with a rather steady stream of moisture into the region.
    Generally lighter snow is forecast for D1 above 4000ft or so
    over northern CA and the Cascades WPC probabilities for at least 6
    inches of snow are medium (40-70%) for these ranges and high
    70%) above 6000ft. By D2, the next heavy snow event enters the
    West as another surge of moisture will aim toward the Sierra with
    PW and IVT values climbing above the 95th percentile per the NAEFS
    ESAT. With a favorable WSW flow into the central/southern Sierra,
    moderate to very heavy snow is likely for areas south of Lake Tahoe
    into D3 as PW/IVT anomalies peak above the 99th percentile. Snow
    levels will rise well above 7000ft to 9000ft (north to south) but
    those high elevations may see several feet of snow over the two-day
    period. WPC probabilities for at least 24 inches of snow are
    highest above 8000ft with the highest peaks possibly receiving
    closer to four feet.

    Farther east, 120-140kt upper jet will stream across the Great
    Basin with the axis of moisture focused across southern NV/UT. This
    will set up favorable westerly flow into the Wasatch and then the
    CO Rockies with moderate-to-heavy snow accumulations on D3 as snow
    levels increase (7500-9000ft). The extended duration of elevated
    moisture and favorable westerly flow could lead to higher
    elevations receiving multiple feet of snowfall by the end of the
    event on Thursday. Currently, WPC probabilities for at least 12
    inches are >50% above 9000ft in the CO Rockies and Wasatch MTs
    through Wednesday morning.


    Snell
    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Nov 25 10:01:00 2024
    FOUS11 KWBC 250743
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    243 AM EST Mon Nov 25 2024

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

    ...Upper Great Lakes to New England...
    Days 1-2...

    Negatively tilted trough over the Upper Midwest along with a closed
    low churning over south-central Canada will slide east today and
    work to provide ample lift over the Upper Great Lakes during the D1
    period. Additionally, broad upper diffluence within the left exit
    region of a zonally oriented upper jet into the central Plains will
    help create the widespread precipitation shield from northern MN
    and WI into the U.P. of MI. Meanwhile, a sure low is expected to
    deepen as it crosses the Great Lakes and enters southern Ontario on
    Tuesday morning with the added forcing to the north of the low. Periods
    of heavy snow with rates up to around 1"/hr are possible associated
    from this low pressure system between northern WI to the U.P. from
    late this afternoon through the evening hours per the 00z HREF
    SPT. Lake -enhanced snowbands are also likely as cold west-
    northwest flow follows in the wake of the low before precipitation
    turns strictly lake-effect on D2. WPC probabilities are high (>70%)
    across the U.P. of Michigan and medium (40-60%) across the MN
    Arrowhead.

    Into New England, which will be dealing with WAA and the passage of
    an occluded front as the low moves into Canada Tuesday, will see some
    of the colder valleys remain below freezing for a period of time
    and allow for light icing. This is most likely to occur near the
    White MTs of northern New England, including parts of VT, NH, and
    ME. PWPF for ice >0.10 inches are about 20-40%.


    ...Pacific Northwest...
    Day 1...

    Upper low off the coast will finally move inland over SW OR and
    weaken on Tuesday, with onshore flow ahead of it for D1 over the
    Cascades where several inches of snow are likely. Snow levels are
    around 3000-4000ft from north to south (WA to OR) and will fall by
    D2 but as QPF wanes and finally moves away from the area. WPC
    probabilities are most notable across the Cascades and Blue Mts in
    OR, as well as the northern CA ranges.


    ...Sierra Nevada...
    Days 1-2...

    Persistent WSW flow will continue for the next few days as waves
    of anomalous moisture flow across the central and especially
    southern Sierra, bringing significant heavy, wet snow to higher
    elevations. Precipitation is beginning to move onshore this morning
    and quickly become heavier today before peaking early Tuesday as
    PW/IVT approach record levels for this time of year per the NAEFS
    ESAT and CFSR period. 700mb 0C line will lie W-E from central CA
    eastward to near UT/AZ border, suggesting high snow levels and
    generally a heavy/wet snow for many areas (and likely lower SLR
    values). NBM shows snow levels around 7500ft (north) to perhaps
    10,000ft (south) coinciding with the heaviest QPF. With >2-3"
    liquid, even at <10:1 ratios, multiple feet of snow are likely in
    the highest elevations along with snowfall rates up to 2-3"/hr.
    Snow levels will drop as QPF starts to decrease towards the end of
    D2 once the shortwave to the north moves out of the Great Basin.
    For the two- day period, WPC probabilities for at least 18 inches
    of snow are high (>70%) above ~8000ft.


    ...Wasatch, CO Rockies...
    Days 1-3...

    Several rounds of forcing in the upper levels and a potent 140 kt
    upper jet initially over UT and CO will impact the region through
    Wednesday and produce widespread heavy mountain snowfall. This
    strong upper flow will also take advantage of ample amounts of
    atmospheric moisture advecting into CA from continued onshore flow
    from the Pacific. IVT values are expected to reach all-time highs
    from southern UT/northern AZ to the Four Corners per NAEFS
    climatological percentiles. Once the zonal jet shifts eastward, a
    strong shortwave trough will approach the area on Wednesday,
    resulting in much heavier snow across the Wasatch and CO Rockies.
    Snow may also bleed over into the CO Front Range as the core of the
    upper jet sinks south, as well as better upslope components on the
    east-facing slopes of the Sangre de Cristo and Sawatch range. Snow
    levels are expected to start out at the beginning of D2 in the
    6000ft-8000ft range (higher south) and rise slightly on D2 before
    falling rapidly below 5000 ft on Day, but while precipitation also
    weakens. In total, multiple days of very favorable forcing and
    continued moisture advection from the Pacific will result in a
    broad 2 to 3 feet of snow over many of the higher elevations of UT
    and CO. WPC probabilities are high (>70%) for at least 24 inches of
    snow during the three day period for elevations in UT and CO above
    10,000ft, with low probabilities (10-30%) of 4 inches of snow
    across the CO Front Range on D3.

    The probability of significant ice >0.25 inches across the CONUS
    is less than 10 percent.

    Snell


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Dec 3 10:39:00 2024
    FOUS11 KWBC 030859
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    359 AM EST Tue Dec 3 2024

    Valid 12Z Tue Dec 03 2024 - 12Z Fri Dec 06 2024

    ...Michigan...
    Days 1-3...

    LES from NNWly flow continues through mid-morning over the eastern
    U.P. and down the western shore of the L.P. Localized additional
    amounts of 4" are possible between 12Z and 18Z in far SW MI given
    the orientation of the flow into that area as well as the current
    radar coverage for the strong banding shifting down Lake Michigan.

    Surface ridging ahead of the next wave spreads over MI today
    shifting flow to the SW and bringing a reprieve to snow this
    afternoon to the state. However, the SWly flow quickly saturates
    and warm air advection snow begins over the U.P. this evening as
    the moisture plume from the next low shifts in. Lake Michigan
    enhancement to this snow will really kick in overnight with
    heavy/repeating snow north from Grand Traverse Bay and over the
    southern shore of the eastern U.P. which continues into Wednesday
    morning. Day 1.5 probabilities for >12" snow are around 60% north
    of Petoskey and across the Mackinac Straits.

    A strong cold front from the low tracking north of the Great Lakes
    sweeps across MI Wednesday afternoon with a quick return to LES
    banding. Potent cold air advection over the Lakes brings heavy
    bands to NW flow prone snow belts into Thursday. Particularly
    strong winds can be expected given the pressure gradient between
    the 990mb low and the 1037mb high over the Dakotas, so impacts will
    be enhanced by the wind. Day 2 PWPF for >6" is 50-80% over the U.P.
    north shore and the NW sector of the L.P. with potential prolonged
    banding southeast from Grand Traverse Bay with a Superior and Lake
    Michigan fetch contributing given the NW flow turning NNWly. LES
    slowly decays and the wind gradiently quickly drops off on
    Thursday.


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

    NWly flow will continue to produce heavy LES over the Chautauqua
    Ridge from fetch over Lake Huron and then over Lake Erie through
    much of today before it diminishes/pivots east as flow shifts SWly
    behind a ridge axis that moves through. An additional 3-6" can be
    expected today over the Chautauqua Ridge area. This afternoon the
    SWly flow will bring snow, possibly banded, to around Buffalo and
    the easten shore of Lake Ontario that persists into the overnight;
    Day 1 PWPF for >4" are 20-40%.


    Days 2/3...

    SWly flow ahead of a developing clipper-type low tracking north of
    the Great Lakes saturates over the interior Northeast, increasing
    coverage and intensity of snow on Wednesday that continues to
    expand and shift north over New England through the overnight. The
    Mohawk Valley/southern Adirondacks are favored for heavier snow
    Wednesday afternoon where the combination of topographic lift and
    antecedant cold air overlap. Higher terrain of the Greens and
    Whites get snow in this time, but the greater coverage is expected
    over central Maine, generally inland from Bangor Wednesday night.
    Day 2 PWPF for >6" is 50-80% over the Mohawk Valley as well as in
    central Maine. The WAA based precip spreads across the rest of
    Maine Thursday morning with a rain/snow line developing interior
    from the Maine coast with a quick transition to heavy snow
    on the cold side.

    The strong cold front crossing Michigan on Wednesday crosses the
    eastern Great Lakes late Wednesday night with a quick onset back to
    heavy snow again on NWly flow off eastern Erie starting before
    sunrise Thursday with aided fetch from Lake Huron. A decent banding
    situation arrises from Lake Ontario over the Tug Hill down the
    Mohawk Valley, possibly overlapping well with the snow from
    Wednesday.Day 2.5 PWPF for >8" is unfortunately 60-90% from Erie Co
    PA to the South Towns of Buffalo. These bands may extend decently
    far inland given the rather strong winds from the 990mb low moving
    into southern Quebec and the 1035mb high over South Dakota Thursday
    morning.

    The low quickly exits to the Canadian Maritimes Thursday with
    guidance wanting to end most of the heavier banding Thursday night.
    Guidance is usually too quick to cut off LES banding, but at least
    in this case the surface high tracking over the Ohio Valley on
    Friday should cause disruption to the bands. Day 3 PWPF for >8" is
    90% over Erie Co PA and around 30% over northern Maine where the
    surface low tracks and for upslope flow over the northern Greens
    and Adirondacks.

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

    Jackson
    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Fri Dec 6 10:44:00 2024
    FOUS11 KWBC 060718
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    218 AM EST Fri Dec 6 2024

    Valid 12Z Fri Dec 06 2024 - 12Z Mon Dec 09 2024

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

    Departing area of low pressure over Atlantic Canada and modest
    high pressure over the Mid-MS Valley will maintain cyclonic flow
    across the Great Lakes, especially off Lakes Erie/Ontario, for the
    next day or two. A shortwave within the broad trough over the
    region will help back the flow enough to instigate another strong
    single band off Ontario into the Tug Hill between Watertown and
    Syracuse this afternoon/evening and overnight. Robust snowfall
    rates of 1-3"/hr (per the HREF) will help deposit another 12-18"+
    of snow over favored areas before waning on Saturday. Downwind of
    Lake Erie, multi-band streamers will result in a larger area of
    light to moderate snow with WPC probabilities of at least another
    6" of snow >50% from Erie, PA northeastward to the Chautauqua Ridge
    in NY.

    Another shortwave rounding the base of the longwave trough will
    slip through the Great Lakes late Sat into early Sun with generally
    light snow for the U.P., northern Lower MI, into NYS and northern
    New England. WPC probabilities for at least 4 inches of snow are
    generally low (10-40%) except for areas with lake enhancement and
    parts of the Adirondacks, Green, and White Mountains where
    probabilities are moderate (40-70%).


    ...Pacific Northwest/Northern Rockies...
    Days 2-3...

    An upper low currently south of the Gulf of Alaska will move
    eastward over the next day or so, aimed toward British Columbia.
    Ahead of it, a plume of moisture will be directed into the Pacific
    Northwest starting early Saturday. Snow levels will start quite
    high (around 8000-9000ft at precip onset very early Saturday) but
    fall to around pass level (~4000ft) late Saturday into the
    overnight hours. East of the crest, cold air in place at the
    surface with overrunning WAA-driven precip supports a wintry mix of snow/sleet/freezing rain for eastern WA. Some icing is possible,
    from a few hundredths to around a tenth of an inch.

    A second surge in moisture will occur on Sunday associated with
    the parent upper low as it opens up across the region. With snow
    levels already around pass level, snow should accumulate on Sunday
    with WPC probabilities for at least 6 inches of snow >50% above
    about 3500ft or so.

    Farther east, moisture will spread across northeastern OR and into
    the northern Rockies from late Saturday through the end of the
    period early Monday. Snow levels will lower through time, and
    nearly all areas except the lowest valleys will change from rain to
    snow. WPC probabilities for at least 8 inches of snow days 2-3 are
    50% above about 5000ft or so, mostly in the Lewis Range and
    across northern ID, the Blue Mountains, and into northwestern WY.


    ...Northern Minnesota and northeastern North Dakota...
    Day 3...

    Eastern extension of the northern Rockies system will manifest
    itself as another upper low forming by Sunday over southern
    Saskatchewan. That will move east-southeastward into early Monday
    with WAA-driven precipitation to its east from northeastern ND
    eastward across northern MN. Ptype will be an issue with milder air
    overtopping the colder boundary layer, especially where precip
    arrives near/after sunset Sunday. NBM ptype uncertainty maximizes
    between all 4 types in a zone along the U.S.-Canadian border though
    the majority of probabilities are either rain or snow. Still,
    cannot rule out some light icing but will have time to narrow the
    forecast with time. WPC probabilities for at least 4 inches of snow
    are moderate (40-70%) over northern MN.


    The probability of significant ice >0.25" across the CONUS is less
    than 10 percent.

    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sat Dec 7 09:49:00 2024
    FOUS11 KWBC 070727
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    227 AM EST Sat Dec 7 2024

    Valid 12Z Sat Dec 07 2024 - 12Z Tue Dec 10 2024

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

    Shortwave on the southwest side of the expansive eastern North
    American trough will zip quickly across the Great Lakes and
    into/through the Northeast later today. With a surface low track
    through southern Ontario, WAA-driven snow will spread across the
    Northeast and end early Sunday. With a general westerly wind
    component, upslope into N-S terrain (e.g., the Green and White
    Mountains) will promote moderate amounts of snow with lighter
    amounts in lower elevations. Some additional lake enhancement is
    also likely off Lake Ontario into the Tug Hill. Quick movement of
    the system should limit amounts, and WPC probabilities for at least
    4 inches of snow are highest (>50%) north of I-90 in NY (Tug
    Hill/Adirondacks) and into the Green and White Mountains. By later
    Saturday night into early Sunday, as the system departs, could see
    some late enhancement over eastern Maine where WPC probs for 4
    inches are also near 50%.


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

    An upper low in the northeast Pacific heading into British
    Columbia will direct two shortwave troughs into the Pacific
    Northwest this weekend. Snow levels will initially start out
    between 8,000-9,000ft this morning, but plummet to as low as
    3,000ft by early Sunday morning. Rain at most locations will change
    to snow at Stevens/Snoqualmie Passes as the first wave of
    precipitation wanes. East of the Cascades, lingering sub-freezing
    temperatures within the boundary layer will be trapped in the
    Columbia Basin as WAA and overrunning moisture aloft provide a
    favorable setup for an icy wintry mix in central and northeastern
    Washington today and even into parts of southeastern
    OR/southwestern ID tonight. Some minor icing accumulations are
    possible up to about a tenth of an inch.

    The second shortwave trough makes its way through the Pacific
    Northwest tonight and into Sunday. Lower snow levels support
    moderate snow at pass level (esp Stevens) with this second wave of
    moisture. WPC probabilities for at least 8 inches of snow are
    highest above about 3500ft.

    These atmospheric disturbances will push their respective plumes
    of moisture east into the Northern Rockies as well, with the
    heaviest snow tonight and into Sunday as snow levels decrease, SLRs
    increase, and northerly low level winds aid in upslope enhancement
    for snowfall rates. Highest probabilities for >6" snow are over
    the terrain including the Bitterroots, Lewis Range, Blue Mountains,
    and into the Little Belt Mountains in central Montana, the
    Absarokas in southern Montana, and the Tetons of western Wyoming.


    ...Northern Minnesota and northeastern North Dakota...
    Days 2-3...

    The first upper level shortwave trough that brought snow to parts
    of the Pacific Northwest mountain ranges will spawn low pressure
    over the Canadian Prairies Sunday morning. As its warm front moves
    east, WAA across the Northern Plains will result in a shield of
    precipitation that passes over a sub-freezing boundary layer. While precipitation may start out as snow along the Canadian border,
    mid/low-level WAA may promote an area of freezing rain for portions
    of eastern ND into MN late tonight into early Sunday. Depending on
    the evolution of the main low along the Canadian border and other
    frontal waviness over the Corn Belt moving up toward the MN
    Arrowhead, snow could be maximized over northeastern MN from north
    of Duluth to the border. WPC probabilities for at least 4 inches of
    snow are >50% from around the Northwest Angle southeastward to
    Embarrass and points northeast.


    ...CO Rockies/Sangre de Cristos...
    Day 3...

    Height falls associated with the second wave through the Pacific
    Northwest will push through the central Rockies, spreading light
    snow across the region on Monday into early Tuesday. Quick movement
    and general lack of moisture will limit snowfall, with WPC
    probabilities of at least 4 inches >30% limited to the Sangre de
    Cristos in CO and just into NM.


    The probability of significant ice >0.25" across the CONUS is less
    than 10 percent.

    Fracasso/Mullinax
    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Sun Dec 8 09:35:00 2024
    FOUS11 KWBC 080812
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    312 AM EST Sun Dec 8 2024

    Valid 12Z Sun Dec 08 2024 - 12Z Wed Dec 11 2024

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

    Quick-moving system crossing from Ontario into Quebec before 12Z
    will continue eastward across northern Maine this morning and early
    afternoon before moving into Atlantic Canada. Light snow is
    forecast after 12Z this morning for the Adirondacks and northern
    New England, with a bit higher amounts over eastern Maine where
    snow will eventually taper off later this afternoon. WPC
    probabilities for at least 4 inches of snow today after 12Z are
    20-40% over far eastern Maine.

    Day 2...

    The next winter storm to affect the region comes from a
    combination of a shortwave over the Ohio Valley and a northern
    stream upper low over southern Canada, both acting in concert to
    coax a moisture plume northward from the Gulf of Mexico on WAA. A
    mix of some freezing rain on the southern side (northeast PA
    northward through NYS and also over parts of western New England)
    and snow on the northern side (north of I-90) may cause some minor
    impacts on Monday. WPC probabilities for at least 4 inches of snow
    are not higher than 10 percent, but are moderate (40-70%) for at
    least 2 inches over northern NH into western ME.

    Day 3... Yet another system will start to affect the Northeast as
    the pattern becomes more amplified in the East. Through 12Z Thu,
    strong WAA should scour out most of the cold air over the region,
    but interior Maine may see some light icing very early Wednesday
    with much more precipitation into D4.


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

    Second part of the two-part system will affect the NW today,
    pushing moisture into a much colder environment. Moderate to heavy
    snow at the higher passes may continue to cause moderate impacts
    this morning before the snow starts to taper off from west to east
    this afternoon. WPC probabilities depict high chances (>70%) for at
    least 8 inches of snow above about 3,500ft while the more remote
    areas above 5,000ft likely receive an additional 12"+ of snowfall.

    Moisture will continue east of the Cascades across to the Rockies
    as the cold front has moved well past the Divide. WPC probabilities
    for >8" of snow are over the higher terrain including the
    Bitterroots, Lewis Range, Blue Mountains, and into the Little Belt
    Mountains in central Montana, the Absarokas in southern Montana,
    and the Tetons of western Wyoming. Snow will continue into D2
    farther east over the Black Hills where probabilities of at least 4
    inches reach 60-90%.


    ...Northern Minnesota and northeastern North Dakota...
    Day 1...

    Low pressure over southern Saskatchewan this morning will move ESE
    toward northern ND/MN this evening and overnight, lifting its warm
    front through the region. While precipitation may start out as
    snow along the Canadian border, mid/low-level WAA may promote an
    area of freezing rain for portions of eastern North Dakota into
    Minnesota this morning, with several hundredths of an inch of ice
    possible after 12Z. Closer to the Canadian border, a colder column
    supports light to modest snowfall, with the heaviest snow occurring
    with the initial WAA over northern Minnesota (esp the Arrowhead,
    which will be enhanced by easterly flow off Lake Superior). WPC
    probabilities for at least 4 inches of snow are >50% across much of
    the northern part of MN, with higher probabilities over the
    Arrowhead (>80%). There, probabilities for at least 8 inches of
    snow are moderate (40-70%).


    ...CO Rockies/Sangre de Cristos...
    Day 2...

    Height falls at the southwest side of a large positively-tilted
    longwave trough over the middle of North America will swing through
    the central Rockies on Monday, brining with it a plume of residual
    Pacific moisture. High pressure building in from the north in the
    wake of a cold frontal passage Monday morning will result in some
    weak upslope flow into Colorado's Front Range during the day. This
    upslope component will extend as far south as the Sangre de Cristos
    in northern New Mexico by Monday night. Periods of light-to-
    moderate snow across the region are expected as the system moves
    quickly through the region and heights build in by Tuesday. WPC
    probabilities show >50% probabilities for at least 4 inches mainly
    limited to the Sangre de Cristos in southern Colorado and northern
    New Mexico, which does include the Raton Mesa. The highest and more
    remote elevations could see localized amounts approach 8" by the
    time the snow comes to an end Tuesday morning.

    The probability of significant ice >0.25" across the CONUS is less
    than 10 percent.

    Fracasso/Mullinax


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Mon Dec 9 10:20:00 2024
    FOUS11 KWBC 090741
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    241 AM EST Mon Dec 9 2024

    Valid 12Z Mon Dec 09 2024 - 12Z Thu Dec 12 2024

    ...CO Rockies/Sangre de Cristos...
    Day 1...

    Height falls moving out of the Great Basin this morning will
    continue southeastward behind a cold front that has pushed into the
    central Rockies. High pressure over the northern Rockies and
    nosing down the High Plains will promote some modest upslope flow
    into Colorado's Front Range during the day today. This upslope
    component will extend as far south as the Sangre de Cristos in
    northern New Mexico by tonight. Periods of snow across the region
    are expected as the system moves quickly through the region and
    heights build in by Tuesday. WPC probabilities are high (>70%) for
    at least 4 inches of snow around the Palmer Divide southward to
    Raton Pass. The highest and more remote elevations could see
    localized amounts around 8-10" by the time the snow comes to an end
    Tuesday morning. Lighter amounts are expected through the I-25
    corridor but could be heavier around Raton Pass.

    ...Northeast...
    Days 1-2...

    Shortwave moving through the Ohio Valley this morning will help
    bring in another surge of moisture coincident with an advancing
    warm front. Sub-freezing air mass largely resides north of I-90,
    along with some higher elevations through the Catskills, this
    morning. As the warm front approaches I-80 this afternoon, an area
    of low pressure will form over southeastern New England, helping to
    maintain some northerly flow over northern New England. However,
    with broad SW to S flow between 850-700mb, warm nose will help
    support areas of freezing rain over eastern NYS into New England
    today, then into Maine D2. Around a tenth of an inch of icing is
    expected D1-2, but WPC probabilities for at least 0.25" are 10-20%
    over western Maine (into the Kennebec Valley). Snowfall may be
    limited with time due to the marginal thermal profile and lack of
    cold enough temperatures in the production zone for dendrites as
    the warm front attempts to push through. A few inches will be
    possible toward precip onset, focusing over the Green/White
    Mountains into Maine where WPC probabilities for at least 4 inches
    are 40-80%.


    Day 3...

    By D3 (Wed-early Thu), upper pattern becomes much more amplified
    upstream as a vigorous system lifts northeastward out of the
    Southeast. Digging upper low into MN will raise heights over the
    East Coast with milder temperatures above freezing ahead of the
    front. On the backside of the front, colder air will filter in atop
    a lagging precip shield, supporting a rain-to-snow transition
    initially over the eastern TN Valley and central/southern
    Appalachians first (Wed afternoon), then eventually into NYS Wed
    evening and overnight into early Thu. WPC probabilities for at
    least 4 inches of snow through 12Z Thu are low to moderate
    (10-40/40-70%) over the central Appalachians (eastern WV) and into
    parts of central NYS into the Adirondacks which will be quicker to
    change over from rain to snow. Additionally, as the low deepens
    quite smartly into Canada, cyclonic flow will wrap across Lakes
    Erie/Ontario as 850mb temps crash to -10 to -15C on westerly flow.
    This will support single banded lake snows by early Thursday,
    continuing beyond this forecast period.


    ...Upper Great Lakes...
    Days 2-3...

    Upstream anticyclonic wave breaking over northwestern Canada will
    support a digging and deep upper low moving into the Great Lakes on
    Wednesday. An arctic front will switch winds to northwesterly as
    much colder air is dragged into the region (850mb temps -15 to -25C)
    which will kick-start the lake-effect snow (LES) machine into
    high gear toward the end of D3 and continuing beyond this forecast
    period. WPC probabilities of at least 4 inches of snow are high
    70%) over much of the northern shore of the Michigan U.P. and
    along the western coast of Michigan's Mitten. For at least 8
    inches of snow, the highest probabilities lie over northwestern
    Lower Michigan. Snowfall rates of 1-2"/hr are likely in more intense bands.


    Fracasso


    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP
  • From Mike Powell@CAPCITY2 to All on Tue Dec 10 08:39:00 2024
    FOUS11 KWBC 100759
    QPFHSD

    Probabilistic Heavy Snow and Icing Discussion
    NWS Weather Prediction Center College Park MD
    259 AM EST Tue Dec 10 2024

    Valid 12Z Tue Dec 10 2024 - 12Z Fri Dec 13 2024

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

    Broad SW flow in the mid-levels to the south/southeast of a
    shortwave nearing James Bay will override a nose of high pressure
    from Atlantic Canada, maintaining sub-freezing low-levels across
    much of central/northern New England this morning. Wavy frontal
    boundary will try to lift northward into the colder air, but will
    be slow to succeed until tomorrow (Wed). As precipitation moves
    into the region overnight tonight into Wednesday morning, freezing
    rain will be likely over much of central/northern New England,
    especially in areas with a little elevation. On Wednesday, southerly/southeasterly flow will eventually win out at the low
    levels, turning all areas over to plain rain. Ice accumulations of
    a tenth or two of an inch are likely over parts of the Green and
    White Mountains and into western Maine where the cold air may hold
    on the longest. WPC probabilities for at least a tenth of an inch
    of ice are >50%. Though the probabilities of at least 0.25" are
    low, this may be underdone as the models are sometimes too quick to
    have the cold air retreat.


    ...Central Appalachians... Day 2...

    The southern part of the system affecting the Northeast tonight
    into Wednesday will be the evolution of an increasingly negatively-
    tilted and deep upper trough over the eastern 1/3 of the CONUS.
    Frontal boundary will clear past the Appalachians tonight, allowing
    colder air to push in behind it and change rain to snow over the
    Cumberland Plateau and points eastward. Upslope enhancement into
    the central Appalachians will promote more modest snow totals, and
    WPC probabilities for at least 4 inches of snow are >30% over
    eastern WV northward through the western MD Panhandle (Garrett Co)
    into the Laurel Highlands in PA.


    ...Northern Plains... Day 1...

    The leading edge of the encroaching Arctic air-mass will track
    into the Northern Plains today. Surface-based warming out in front
    of the Arctic front and strong CAA aloft will allow for lapse rates
    in the 500-700mb layer to be >7.5C/km in some cases, with just
    enough low-level moisture for some snow squalls to develop. These
    squalls could form as far north and west as eastern Montana and
    western North Dakota this morning then race southward and eastward
    into South Dakota this afternoon and the Missouri Valley by this
    evening. Squalls could even continue to track into parts of Iowa,
    northern Kansas, and northern Missouri tonight as the snow squall
    parameter exceeds 1 in much of the CAM and even global guidance.
    Though snow amounts will be light, squalls can lead to rapid
    reductions in visibility with accumulating snow on roadways where
    road temperatures drop below freezing and create icy hazards.


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

    Upper pattern will become increasingly amplified over the East as
    ridging into the West weakens but builds quite smartly over the
    northern Atlantic. This will help strengthen the jet to ~170kts out
    of the southwest across the TN/OH Valley overnight tonight as
    arctic air moves in from the northwest. Lake effect snow will pick
    up in earnest starting this evening and overnight across the U.P.
    of Michigan and then into the western side of Lower Michigan as
    height falls rush through (500mb heights below the 1st percentile
    per the CFSR) as the trough axis becomes quite negatively-titled
    into the Southeast/Mid-Atlantic. 850mb temperatures will plunge to
    -15C to -25C tomorrow with plenty of Lake-to-850 DeltaT. Snow will
    continue through the period as winds slowly back from NW to WNW or
    W as the upper center passes by. Into the Northeast, once the
    front clears the area and temperatures fall below freezing area-
    wide, snow will increase off Lakes Erie/Ontario, the latter of
    which will support a strong single band into the Tug Hill Plateau
    with lighter snow pretty far inland. Snow off Lake Erie may also
    be a single banded aimed just into the BUF southtowns. Snow will
    continue across all the Great Lakes through the end of this period
    (12Z Fri) but will continue beyond then.

    Through 12Z Fri, WPC probabilities of at least 12 inches of snow are
    high (>70%) across the favored lake belts on NW flow over the U.P.
    and northwest Michigan; between Erie, PA and Buffalo, NY (esp the
    southtowns but perhaps into the southern Buffalo area); and in the
    Tug Hill. Snowfall rates of 1-2"/hr (surpassing 3"/hr at times) are
    likely in the more intense bands.


    ...WA/OR Cascades... Day 3...

    Incoming shortwave or upper low will move into NorCal/Southwestern
    OR Thursday, spreading some precipitation into the Cascades
    southward into the Sierra. Snow levels will be around 3000ft to the
    north and 5000ft to the south with QPF totals generally up to
    0.50" or so. WPC probabilities for at least 6 inches of snow are
    highest in the WA/OR Cascades.

    Fracasso

    $$
    ---
    * Synchronet * CAPCITY2 * capcity2.synchro.net * Telnet/SSH:2022/Rlogin/HTTP