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Mesoscale Discussion 193
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   Mesoscale Discussion 0193
   NWS Storm Prediction Center Norman OK
   0249 PM CDT Wed Mar 18 2020

   Areas affected...Parts of the Texas South Plains and Big Country
   into the Red River Valley

   Concerning...Severe potential...Watch likely 

   Valid 181949Z - 182145Z

   Probability of Watch Issuance...80 percent

   SUMMARY...The initiation of discrete thunderstorm development
   appears increasingly likely by 6-7 PM CDT, and could commence as
   early as 4-5 PM CDT across the Big Country near Abilene, in an
   environment increasingly conducive to the formation of supercells.
   The primary severe hazards initially are probably large hail and
   locally strong surface gusts, but potential for tornadoes could
   begin to increase by early evening.

   DISCUSSION...Southwesterly mid/upper flow remains broadly
   anticyclonic with rising mid-level heights across much of the
   region.  However, it is and should remain at least weakly difluent,
   and model output continues to suggest this may transition at
   mid-levels to broadly cyclonic with weak height falls, as a subtle
   perturbation overspreads the region by 21-00Z.  As this occurs,
   there probably will be at least some tempering of increasing
   lower/mid tropospheric inhibition, which is ongoing in association
   with the northward advection of warmer elevated mixed-layer air.

   Daytime heating of a moist boundary layer (surface dew points in the
   lower to mid 60s) already appears to be contributing to mixed-layer
   CAPE of 1000-2000 J/kg, as winds around 500 mb begin to increase to
   40-50 kt.  By the time storms initiate, the environment probably
   will be conducive to supercells.

   Low-level forcing to focus and support thunderstorm initiation
   remains a little unclear, but weak low-level warm advection may 
   contribute to lift.  Convection allowing guidance, particularly the
   last few runs of the High Resolution Rapid Refresh, suggest
   convection may initiate across the Big Country, near Abilene, as
   early as 21-22Z.

   Low-level hodographs are initially rather modest in size, and may
   remain so until after 00-02Z, when near surface wind fields may
   begin to back to south/southeasterly, while 850 mb flow begins to
   strengthen to 30-40 kt, as the primary upstream short wave begins to
   accelerate toward the Southwestern international border area. 
   However, strongest storms may still pose a risk for large hail,
   locally damaging wind gusts and perhaps a brief tornado or two into
   early evening.

   ..Kerr/Dial.. 03/18/2020

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

   ATTN...WFO...FWD...OUN...SJT...LUB...MAF...

   LAT...LON   34320009 34229790 33399738 32459856 30919950 30950086
               31770126 34320009 

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Page last modified: March 18, 2020
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