• MESO: Mesoscale Discussion 0605

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Thu May 13 19:38:42 2021
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    ACUS11 KWNS 131938
    SWOMCD
    SPC MCD 131938=20
    NEZ000-SDZ000-WYZ000-132215-

    Mesoscale Discussion 0605
    NWS Storm Prediction Center Norman OK
    0238 PM CDT Thu May 13 2021

    Areas affected...Parts of northern/western Nebraska and adjacent
    portions of southeastern Wyoming and southwestern South Dakota

    Concerning...Severe potential...Watch unlikely=20

    Valid 131938Z - 132215Z

    Probability of Watch Issuance...20 percent

    SUMMARY...Strong thunderstorm development, possibly including an
    evolving cluster of storms, appears underway. This may pose a risk
    for hail and strong surface gusts which could occasionally approach
    or exceed severe limits into early evening. Due to the marginal
    anticipated risk, it is not clear that a severe weather watch is
    needed, but trends will be monitored.

    DISCUSSION...Boundary-layer destabilization is underway across
    central portions of the high plains, modest due to low moisture
    levels, but becoming maximized as far north as the Nebraska
    Panhandle vicinity. This is generally north and east of a
    developing weak surface low, and along a strengthening zone of
    differential surface heating, which is becoming a focus for
    deepening convective development. This is probably being supported
    by increasing large-scale ascent, largely due to low/mid-level warm
    advection, downstream of a low-amplitude mid-level perturbation
    digging within northwesterly flow across the northern Rockies.

    Deep-layer ambient mean flow only appears to be strengthening from
    20-30 kt, but associated vertical shear, aided by veering profiles
    in low to mid-levels, is probably becoming conditionally supportive
    of organized convection. With mixed-layer CAPE, particularly around
    the Alliance, NE vicinity, as high as 500 J/kg, but up to around
    1000 J/kg for surface-based parcels, there appears potential for at
    least a few stronger storms capable of producing small to marginally
    severe hail.=20=20

    Given the steep low-level lapse rates associated with the modestly
    deep, well mixed boundary-layer, locally strong surface gusts might
    be the more prominent convective hazard, aided by sub-cloud cooling
    associated with melting and evaporating precipitation. It is
    possible that forcing associated with consolidating surface cold
    pools, coupled with the larger-scale ascent, could support an
    upscale growing, southeastward propagating cluster of storms by
    early evening.

    ..Kerr/Thompson.. 05/13/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!uzo11vCru5AZsTEMIKud-9xo6qu7eYBFJNnsXZusRQCbp2rbDrLYDhPD9vW2ZSKJraqF7rFP$=
    for graphic product...

    ATTN...WFO...LBF...UNR...CYS...

    LAT...LON 43560347 42309958 41460155 41340384 42450404 42920451
    43560347=20



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