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Mesoscale Discussion 215
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   Mesoscale Discussion 0215
   NWS Storm Prediction Center Norman OK
   0558 PM CST Sun Feb 26 2017

   Areas affected...Parts of central TX

   Concerning...Severe potential...Watch unlikely 

   Valid 262358Z - 270200Z

   Probability of Watch Issuance...5 percent

   SUMMARY...Developing thunderstorms near the Austin/San Antonio metro
   may pose a very isolated risk for hail, gusty winds, and perhaps
   even a brief tornado over the next several hours. Watch issuance is
   not expected at this time.

   DISCUSSION...Visible satellite loops from the past few hours have
   shown an area of weak low-level confluence and agitated cumulus
   field over central TX. Better low-level moisture (surface dewpoints
   in the lower to mid 60s) has developed northward from south TX and
   the western Gulf through the day, and steep mid-level lapse rates
   present on the 12Z DRT sounding have advanced eastward over central
   TX. With some diurnal heating, MLCAPE of 500-1000 J/kg is presently
   located across the discussion area, decreasing with northward extent
   due to more limited moisture.

   Large-scale forcing for ascent is also increasing across central TX
   with the approach of a low-amplitude shortwave trough from the west.
   Strong westerly to southwesterly mid-level winds attendant to this
   trough are contributing to 50-55 kt of effective bulk shear, which
   is more than sufficient for supercell structures. Indeed, several
   low-topped supercells have been observed per the KEWX radar between
   Austin and San Antonio over the past hour or two. Main limiting
   factor that has suppressed more robust thunderstorm development so
   far has been pronounced mid-level capping centered between 850-700
   mb. Even so, with continued low-level moistening and mid-level
   cooling forecast to occur over the next several hours, these
   developing thunderstorms may eventually breach the cap and pose a
   very isolated risk for hail approaching severe levels, strong/gusty
   winds, and perhaps even a brief tornado given effective SRH of
   200-250 m2/s2 across central TX.

   ..Gleason/Edwards.. 02/26/2017


   LAT...LON   29559826 30869757 30839720 30589689 29859680 29409737
               29359814 29559826 

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