SPC AC 121955

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0255 PM CDT Mon Apr 12 2021

   Valid 122000Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON THROUGH LATE THIS EVENING ACROSS THE EDWARDS PLATEAU AND
   VICINITY...

   ...SUMMARY...
   A few afternoon and evening thunderstorms will produce isolated very
   large hail and locally damaging winds across the Edwards Plateau and
   vicinity in Texas.

   ...20Z Update...
   No changes have been made to the Slight Risk area across the Edwards
   Plateau region of TX. It appears that convective initiation will
   probably occur within the next few hours (by 22-23Z) between San
   Angelo and Junction TX. Visible satellite imagery shows a cumulus
   field has developed across this area in the vicinity of a cold
   front. Latest RAP forecast soundings suggest minimal capping
   remaining by 22Z, and weak low-level convergence along the front
   should be enough to initiate at least a couple of storms.
   Environmental conditions still appear favorable for isolated very
   large hail with any supercells that can form this afternoon/early
   evening, as moderate to strong instability, steep mid-level lapse
   rates, and sufficient deep-layer shear will all be present.
   Occasional strong to severe wind gusts from convective downdrafts
   may also occur as low-level lapse rates continue to steepen
   along/south of the cold front.

   ..Gleason.. 04/12/2021

   .PREV DISCUSSION... /ISSUED 1118 AM CDT Mon Apr 12 2021/

   ...Central TX area late this afternoon into tonight...
   A series of subtle southern-stream shortwave troughs will move
   east-northeastward from northern Mexico/far west TX/southern NM over
   western/northern TX and OK through tonight.  At the surface, a cold
   front will continue to move southward across north and central TX,
   while low-level moisture spreads north-northwestward in advance of
   the front.  Satellite imagery suggests that the strongest surface
   heating will occur south of I-20, where afternoon temperatures of
   85-90 and boundary-layer dewpoints near 60 will support MLCAPE of
   2500 J/kg.  Widely scattered thunderstorm development is expected in
   the zone of low-level ascent and minimized convective inhibition
   along the front late this afternoon across the Edwards Plateau, with
   the large buoyancy and relatively straight/long hodographs and
   midlevel lapse rates greater than 8 C/km favoring splitting
   supercells capable of producing isolated very large hail (greater
   than 2.5 inches in diameter) and isolated damaging winds.  Some of
   the left-moving storms could progress as far as north TX prior to
   weakening this evening, and additional elevated convection (with a
   low-end hail threat) may form atop the frontal surface early tonight
   from north TX into southeastern OK.

   Farther south, supercell development is also expected along the east
   slope of the Serranias del Burro (west of Del Rio), and the storms
   will make it near or just across the Rio Grande before weakening.

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