SPC AC 221937

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0237 PM CDT Wed Apr 22 2020

   Valid 222000Z - 231200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
   AFTERNOON AND EVENING ACROSS PARTS OF SOUTHEASTERN OKLAHOMA AND MUCH
   OF NORTHEAST TEXAS THROUGH SOUTHWESTERN ARKANSAS...NORTHERN
   LOUISIANA AND PARTS OF WESTERN MISSISSIPPI...

   ...SUMMARY...
   Supercells capable of producing severe hail and a few tornadoes
   appear increasingly likely through early evening across southeastern
   Oklahoma and portions of eastern Texas into Louisiana.  Thereafter,
   a gradually organizing cluster of storms may spread into the lower
   Mississippi Valley overnight, accompanied by a continuing risk for
   damaging wind gusts and tornadoes.

   ...20Z Outlook Update...
   There is no appreciable change to the prior outlook concerning
   severe weather potential.

   Mid-level inhibition associated with warm elevated-mixed layer air
   remains prominent across much of southern and eastern Texas. 
   However, lower/mid tropospheric thermal and moisture advection to
   the northeast of this air mass has contributed to increasingly
   widespread convective development across northeastern Texas into
   northern Louisiana and southern Arkansas.  At the same time,
   convection has become widespread to the north of a warm frontal zone
   roughly along/north of the I-40 corridor of Oklahoma into Arkansas.

   Strong boundary-layer destabilization has become focused along an
   eastward advancing dryine, trailing south of a slowly deepening
   surface cyclone near the Red River, where the leading edge of
   mid-level cooling is beginning to weaken the mid-level inhibition. 
   Strong boundary-layer destabilization has also occurred beneath the
   stronger mid-level inhibition, across much of Deep South Texas into
   the vicinity of the southern flank of the warm advection convection,
   now roughly north of College Station into the Jasper vicinity.  This
   also coincides with the leading edge of low-level moisture return,
   in the wake of recent frontal passages associated with amplified
   troughing now shifting east of the Atlantic Seaboard.

   Into this evening, it appears that both the eastward advancing
   dryline, across and east of the I-35 corridor of southern Oklahoma
   into northern Texas, and the developing effective surface warm
   frontal zone north of the upper Texas coastal plain into central
   Louisiana will become the focus for intensifying severe thunderstorm
   development.  This probably will include a few discrete supercells
   and one or two organizing clusters which may progress into the lower
   Mississippi Valley overnight.

   ..Kerr.. 04/22/2020

   .PREV DISCUSSION... /ISSUED 1127 AM CDT Wed Apr 22 2020/

   No changes have been made to the ongoing outlook areas.

   ...East TX into LA today...
   Scattered thunderstorms have begun to form in central TX beneath the
   sub-tropical jet.  A very moist boundary layer beneath steep lapse
   rates will provide ample CAPE for hail this afternoon in the
   strongest cells.  Considerable shear and helicity also pose an
   increasing risk of a few tornadoes this afternoon as storms spread
   into LA. Refer to MCD #436 for further details.

   ...Eastern OK/Western AR early this afternoon...
   Scattered strong to severe storms have been occurring over eastern
   OK this morning, in a region of strengthening low-level warm
   advection and lift ahead of an approaching shortwave trough.  The
   strong cells/clusters may continue to pose a risk of large hail
   through the early afternoon as they move into western AR and slowly
   weaken.  

   ...Central OK into North TX this afternoon/evening...
   A well-defined dryline is expected to develop this afternoon over
   southwest OK and western north TX - mixing eastward to roughly I-35
   by 22z.  Very steep lapse rates and dewpoints at least in the mid
   60s will yield a corridor of strong MCAPE with values over 3500 J/kg
   and little inhibition.  This will likely result in the development
   of a few supercells roughly between OKC and FTW.  Very large hail
   will be possible with this activity, as well as a few tornadoes
   (including strong tornadoes).  These supercells will likely persist
   into the evening and track across southeast OK and northeast TX.

   ...ArkLaTex overnight...
   Storms will likely congeal in the late evening over northeast TX and
   surge eastward overnight across parts of AR/LA and eventually into
   MS.  These storms will have an increasing risk of damaging winds,
   along with continued threats of hail and tornadoes.

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