• MESO: Mesoscale Discussion 0435

    From COD Weather Processor@1:2320/105 to wx-storm@lists.illinois.edu on Tue Apr 27 18:17:28 2021
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    ACUS11 KWNS 271817
    SWOMCD
    SPC MCD 271817=20
    OKZ000-TXZ000-272015-

    Mesoscale Discussion 0435
    NWS Storm Prediction Center Norman OK
    0117 PM CDT Tue Apr 27 2021

    Areas affected...Portions of west/northwest TX and western/central
    OK

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

    Valid 271817Z - 272015Z

    Probability of Watch Issuance...80 percent

    SUMMARY...The threat for large hail, damaging wind gusts, and
    perhaps a couple tornadoes is expected to increase this afternoon.
    Some of the hail may be very large (2+ inches in diameter). Watch
    issuance is likely.

    DISCUSSION...Towering cumulus has begun to form early this afternoon
    along a dryline across parts of west TX to the south of Lubbock,
    with lightning recently noted with a recent attempt at initiation in
    Lynn County TX. Current expectations are for additional convective
    development to occur in the next couple of hours across portions of
    west TX along/near the dryline as weak ascent associated with
    multiple small-scale mid-level perturbations overspreads the
    southern High Plains and continues to erode the cap. Rather steep
    (8-8.5 C/km) mid-level lapse rates are present across much of
    west/northwest TX into central OK per area 12Z soundings. These
    steep lapse rates aloft combined with strong mid/upper-level flow
    suggest supercells capable of producing large hail will be the main
    threat initially. The boundary-layer still appears capped farther
    east into western north TX and western OK per latest mesoanalysis
    estimates. Still, visible satellite imagery is showing some breaks
    in the cloud deck, with temperatures warming into the mid/upper 70s
    as of 18Z. As diurnal heating continues, the development of
    1500-2000 J/kg of MLCAPE appears likely by mid afternoon across much
    of the warm sector along and east of the dryline.

    Some convection-allowing guidance suggests that substantial
    mixing/drying of the boundary layer will occur this afternoon across
    parts of west/northwest TX where the depth of the low-level moisture
    return remains shallow. Some evidence of this may already be
    occurring near San Angelo TX per recent surface observations. If
    this trend continues, then a relatively narrow corridor may exist
    for severe storms to develop, roughly from the vicinity of Lubbock
    towards Childress TX. Still, as storms move northeastward into
    western/central OK, they should encounter increasing low-level
    moisture, greater instability, and strong deep-layer shear. This
    favorable environment will likely support storm organization, with
    large to isolated very large hail possible with any supercells.
    Although low-level flow is not forecast to be overly strong through
    the afternoon, a modest increase in a south-southwesterly low-level
    jet may occur by early this evening across parts of western OK and
    vicinity. If this occurs and convection can remain at least
    semi-discrete, then a couple of tornadoes appear possible given the
    expected increase in low-level shear. Some increase in the damaging
    wind threat may also develop with time if storms congeal into one or
    two small bowing clusters. Regardless of eventual convective
    evolution, an increasing severe threat across this region will
    likely warrant watch issuance.

    ..Gleason/Hart.. 04/27/2021

    ...Please see https://urldefense.com/v3/__http://www.spc.noaa.gov__;!!DZ3fj= g!tSle1RZomw39_fcgYhJ6_0ksopttw6qT6l1RJj0gEJO8I6URNMu_zG-PJqjNO2HfH0EAOC7L$=
    for graphic product...

    ATTN...WFO...OUN...LUB...AMA...MAF...

    LAT...LON 33120085 32840165 32770197 33220188 33510170 33850133
    34420094 35559994 36169918 36579840 36719777 36529719
    36149694 35509705 34829780 34189865 33459984 33120085=20



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