SPC AC 231958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0258 PM CDT Fri Apr 23 2021

   Valid 232000Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
   OF THE SOUTHERN PLAINS INTO THE GULF COAST STATES...

   ...SUMMARY...
   Severe wind, large to very large and destructive hail, and a few
   tornadoes are possible today and tonight across parts of the
   southern Plains to lower Mississippi Valley.

   ...Southern portion of Gulf Coast states...

   Primary change to previous forecast has been to extend the ENH risk
   area farther east along southern portions of the Gulf Coast states.
   Storms that develop over TX this afternoon are expected to evolve
   into an MCS with likelihood of embedded organized storm structures
   especially on the southern end near advancing warm front this
   evening into the overnight. An intense 60 + kt southwesterly
   low-level jet accompanying the progressive shortwave trough will
   support large 0-2 km hodographs within a strongly sheared
   environment. Bowing segments and embedded supercells capable of
   damaging wind and a few tornadoes will be the main threats.

   ..Dial.. 04/23/2021

   .PREV DISCUSSION... /ISSUED 1113 AM CDT Fri Apr 23 2021/

   ...TX early this afternoon...
   Morning water vapor loop shows a trough progressing across AZ/NM and
   northern Mexico into TX.  Large-scale lift associated with this
   trough will begin to overspread an increasingly moist/unstable air
   mass over central TX by early afternoon - leading to scattered
   thunderstorm development.  Forecast soundings from north-central to
   south-central TX show steep mid-level lapse rates and sufficient
   CAPE to pose a risk of hail in the stronger cells.  Low and mid
   level winds are also sufficiently strong for a threat of
   gusty/damaging winds.  

   ...Southeast TX into LA/MS/AL this evening and tonight...
   A strong southerly low-level jet is forecast to develop after dark
   across far southeast TX and southern LA.  This will help to focus
   lift and shear along precipitation-reinforced boundary that will
   extend across the region.  Most CAM solutions show multiple
   bow/supercell structures tracking along the boundary through the
   evening and overnight into parts of southern MS/AL.  Present
   indications are that damaging winds will be the main threat with
   these storms.  However, there is increasing concern for a greater
   tornado risk as well - both supercellular and QLCS.  Will maintain
   5% tornado probabilities at this time but may introduce higher
   probabilities at 20z if confidence of the narrow corridor of threat
   increases.

   ...Southeast TX Panhandle into Southern OK...
   Southeasterly low-level winds continue to transport increasingly
   moist/unstable air northward into the eastern TX panhandle and
   southwest OK.  This will lead to the development of scattered
   intense thunderstorms this afternoon and evening.  Forecast
   soundings show very steep lapse rates and robust CAPE profiles,
   along with strong deep-layer shear.  This should promote supercells
   capable of very large hail and a tornado or two.  Activity is
   expected to persist through the evening and spread eastward across
   central/southern OK with an increasingly linear nature, along with
   the potential of more widespread damaging wind risk.

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