• MESO: Mesoscale Discussion 1839

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Oct 12 20:08:37 2021
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    ACUS11 KWNS 122008
    SPC MCD 122008=20

    Mesoscale Discussion 1839
    NWS Storm Prediction Center Norman OK
    0308 PM CDT Tue Oct 12 2021

    Areas affected...portions of the central High Plains

    Concerning...Severe potential...Tornado Watch likely=20

    Valid 122008Z - 122145Z

    Probability of Watch Issuance...95 percent

    SUMMARY...Strong ascent ahead of an advancing upper low will support
    rapid destabilization and storm development late this afternoon and
    into this evening. Supercells with all hazards including tornadoes
    are possible. A tornado watch is likely late this afternoon.

    DISCUSSION...As of 1955 UTC, a well-defined upper low was located on
    WV imagery near the Four Corners region moving east. To the south of
    the low, an 80-100 kt mid-level speed max was observed rounding the
    base and ejecting into southern CO. To the north and east of the
    low, strong ascent (90-120 DM 12 hr H5 height falls) is supporting
    widespread precipitation across the central and northern Rockies. In
    response to the powerful dynamics aloft, already strong low-level
    pressure gradients are forecast to strengthen rapidly allowing a
    relatively warm/moist surface airmass to advect ahead of the
    dryline/surface trough supporting destabilization late this

    Mid and lower 50s F surface dewpoints at the nose of deeper surface
    moisture, have already been observed across southwestern KS as far
    north as TQK. Continued warm/moist advection beneath the cold-core
    of the upper low will support rapid destabilization (MLCAPE values
    of 500-1250 J/kg) by 23-01z given steep mid-level lapse rates near
    8.5 C/km. Late afternoon/early evening model soundings also show
    very strong and veering wind profiles developing beneath the
    mid-level jet, with largely boundary-normal effective shear values
    of 60-70 kt supportive of discrete supercells. Low-level shear is
    also likely to be strong beneath a 50-60 kt low-level jet. Model
    soundings show large looping hodographs (ESRH 300-400 M2/s2)
    favorable for strong low-level mesocyclone development. Given the
    overall parameter space and potential for strong supercells, a risk
    for tornadoes (some significant), large hail, and damaging winds
    appears likely to develop by 22-00z.=20

    Latest observational trends suggest hi-res guidance remains too cool
    and dry across much of the High Plains where rapid
    warming/moistening is occurring. This lends high confidence in
    eventual destabilization of the airmass as the upper low approaches
    late this afternoon. Deep convection should gradually evolve out of
    the initial updrafts ongoing in the elevated cumulus field across
    eastern CO. Weaker buoyancy and storm motions more parallel to the
    northern sections of the dryline suggest initial storm mode may
    remain linear, though a gradual transition to more isolated
    convection is expected with southern extent. Fast-moving long-track
    supercells capable of all hazards should evolve rapidly and
    intensify as they move through the narrow, but unstable and strongly
    sheared warm sector after dark. Given the potential for significant
    severe weather, a tornado watch will likely be needed late this

    ..Lyons/Grams.. 10/12/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!qzrQt7ZJ7zETuwb8yNrEsXZ1aBrg3dWqZj_Cl_t9O8XsDuCLF_APDrA1e2dB2g9LJwhGdoH1$=
    for graphic product...


    LAT...LON 36480181 36790197 37160211 37660219 38110231 38840240
    40060256 40510266 40770261 40960246 40970228 40900200
    40740169 40430136 39860108 39210076 38450049 37810030
    37370021 37220026 37010031 36760045 36610065 36540080
    36470097 36460128 36480153 36480181=20

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