• MESO: Mesoscale Discussion 0013

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Wednesday, January 09, 2019 10:26:26
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    ACUS11 KWNS 090926
    SWOMCD
    SPC MCD 090925
    MEZ000-NHZ000-VTZ000-091530-

    Mesoscale Discussion 0013
    NWS Storm Prediction Center Norman OK
    0325 AM CST Wed Jan 09 2019

    Areas affected...portions of VT...NH and western ME.

    Concerning...Heavy snow

    Valid 090925Z - 091530Z

    SUMMARY...A belt of increasingly heavy snow, with rates commonly 1-2 inches/hour and locally/briefly higher, should pivot across this
    corridor from southwest to northeast through mid/late morning local
    time. Brief mixed precipitation, including light freezing rain, is
    possible around the south and east edges.

    DISCUSSION...A low/middle-level cyclone, manifest on the 9Z surface
    chart by a binary low with diffuse pressure minima near PSF and SLK,
    is expected to deepen and consolidate as it crosses southern VT/NH
    through dawn, reaching the ME coastline near PWM around 12Z, then
    moving slowly up the coast thereafter with continued deepening. As
    the low-level cyclone intensifies, mass response will likewise
    strengthen, including the combination of elevated forcings in the
    conveyor occupying its proximal northern semicircle.

    Meanwhile, large-scale lift forced from higher aloft -- contributed
    by both DCVA immediately preceding the mid/upper trough/low and
    left-exit region of a cyclonically curved/eastward-shifting jet
    streak south of southern New England, will contribute to deep
    columnar cooling. As evident in time series of forecast soundings,
    this process will freeze layers above the surface (near 850 mb) that
    initially are warmer than 0 deg C, effecting transition of sporadic
    freezing rain on the eastern rim of the advancing precip area to
    snow. As deep-layer lift from multiple sources strengthens in the dendritic-growth zone, snowfall rates should increase beneath the
    laterally expanding and vertically deepening area of ice-phase
    precip production. Steep midlevel lapse rates within a column that
    is saturated (or very nearly so) also may support development of
    transient lenses of weak MUCAPE, supporting embedded convective
    elements and locally contributing to short-lived bursts of snow
    rates topping 2 inches/hour, especially at higher ground elevations.

    ..Edwards.. 01/09/2019

    ...Please see www.spc.noaa.gov for graphic product...

    ATTN...WFO...GYX...BTV...ALY...

    LAT...LON 43907285 44307248 44757187 44927171 45147153 45277128
    45237085 44827013 44347010 43907047 43217150 43247297
    43477323 43907285



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