Mesoscale Discussion 0453
   NWS Storm Prediction Center Norman OK
   0242 PM CDT Wed Apr 28 2021

   Areas affected...Portions of south-central TX

   Concerning...Severe potential...Watch likely 

   Valid 281942Z - 282145Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms capable of producing very large hail,
   damaging wind gusts, and perhaps a few tornadoes are expected to
   develop this afternoon. Watch issuance will likely be needed.

   DISCUSSION...Persistent low-level east-southeasterly upslope flow is
   occurring this afternoon across south-central TX. This will support
   convective initiation across the higher terrain of northern Mexico
   adjacent to Del Rio TX. In fact, several attempts have recently
   occurred along the Rio Grande River in Val Verde County, and a
   lightning flash has been observed with developing convection in
   adjacent northern Mexico. Rich low-level moisture, characterized by
   upper 60s to low 70s surface dewpoints, is in place across this
   region. This moisture coupled with strong diurnal heating and
   steepening mid-level lapse rates is supporting MLCAPE of 1500-2500
   J/kg east of a surface dryline.

   Enhanced mid-level flow associated with an upper low over the
   Southwest and northern Mexico will remain over this region through
   the afternoon and evening. Related strong effective bulk shear of
   50-60+ kt and long, straight hodographs above the boundary layer
   will support supercells, with some potential for storm splits. Very
   large hail of 2 to 3+ inches appears likely with these initially
   discrete storms given the rather favorable thermodynamic and
   kinematic environment. As additional storms form through the late
   afternoon and into early evening, severe wind gusts may also occur
   given the presence of steep low-level lapse rates where strong
   diurnal heating has occurred. Although low-level winds across
   south-central TX are not forecast to be very strong, there will be
   ample directional shear/veering of the wind profile though the
   boundary layer. This should support low-level rotation with any
   supercells that can form, and isolated tornadoes appear possible.
   Watch issuance will likely be needed to address this anticipated
   severe threat.

   ..Gleason/Hart.. 04/28/2021

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

   ATTN...WFO...EWX...SJT...

   LAT...LON   29730153 30150129 30420067 30599987 30719900 30719844
               30429823 29959841 29229917 28569999 28570048 29010072
               29300099 29730153