SPC AC 211956

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0256 PM CDT Thu May 21 2020

   Valid 212000Z - 221200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM WESTERN
   KANSAS INTO NORTHWEST OKLAHOMA...

   ...SUMMARY...
   Scattered severe thunderstorms are expected this afternoon and
   evening over the central High Plains and parts of west Texas. Other
   isolated severe thunderstorms are possible over southern Florida and
   the Carolinas.

   ...Central Plains...
   A slight extension was made to the Slight Risk across northern
   Oklahoma and far south-central Kansas in anticipation of a
   well-advertised nocturnal MCS. Large elevated instability will
   develop ahead of storms forming over western Kansas this evening,
   which will likely support an eventual southeastward-propagating MCS
   with damaging wind threat. While storm mode will not be particularly
   favorable for hail, very steep lapse rates aloft may support
   marginally severe hail in the strongest storm cores. For more
   information see MCD #651.

   ..Jewell.. 05/21/2020

   .PREV DISCUSSION... /ISSUED 1101 AM CDT Thu May 21 2020/

   ...Western KS and Vicinity...
   Southwest flow aloft is present today over most of the Plains
   states, with weak midlevel height falls expected to spread into
   parts of KS and the TX Panhandle later today.  A weak surface low is
   currently analyzed over western KS, and should stay stationary or
   move slowly southward this afternoon as a front sags southward
   across eastern CO.  The capping inversion is strong this morning,
   but is forecast to weaken rapidly by mid-afternoon as a combination
   of large scale forcing, daytime heating, and low-level moisture
   return occur.

   Current indications are that storms will initiate along the surface
   cold front, and near the surface low/triple-point, over western KS
   before 21z.  Forecast soundings suggest steep midlevel lapse rates
   and MLCAPE over 2000 J/kg.  Large hail will be the primary threat
   with initial storms, with a risk of isolated very large hail. 
   Vertical shear profiles are not particularly strong, but should be
   sufficient for a few supercells during the late afternoon.  Activity
   will likely congeal into a bowing MCS after dark, spreading into
   southwest KS and northwest OK with a risk of damaging winds.

   ...Central TX...
   Water vapor imagery shows a shortwave trough moving eastward across
   central TX this morning.  Clear skies and veered low-level winds are
   present to the west of the trough across west TX.  By
   late-afternoon, full sunshine will lead to strong instability and a
   deeply mixed boundary layer along the dryline near Abilene/San
   Angelo.  However, convergence will be quite weak and convective
   initiation is highly uncertain.  Will maintain portions of the
   ongoing SLGT risk due to a conditional risk of hail and damaging
   wind gusts if storms can form.  But confidence is low for this area.

   ...FL...
   Strong heating is occurring this morning over the FL peninsula,
   where dewpoints in the 70s and rather cool temperatures aloft will
   yield afternoon MLCAPE values over 2500 J/kg.  Thunderstorms are
   expected to form first over south FL, then develop northward along
   the instability axis.  Wet microbursts capable of gusty/damaging
   wind gusts and occasional hail appear to be the main risks. 
   Midlevel winds and low-level shear are weak, limiting convective
   organization and the risk of a more robust severe event.

   ...Carolinas...
   Scattered afternoon thunderstorms are expected over the eastern
   Carolinas, where scattered breaks in the clouds and dewpoints in the
   60s will develop later today.  Easterly surface winds along/north of
   a warm front may lead to transient supercell structures capable of
   gusty winds or even a brief tornado.  However, weak flow aloft
   should limit overall several potential.

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