SPC AC 281933

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0233 PM CDT Wed Apr 28 2021

   Valid 282000Z - 291200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF TEXAS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM TEXAS INTO
   SOUTHERN IL/WESTERN KY AND ACROSS PARTS OF THE LOWER GREAT LAKES...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the southern
   Plains to southwest Texas through this evening. Other severe storms
   may develop in parts of the lower Great Lakes region.  In both
   areas, the most intense thunderstorms may produce large hail and
   wind damage.  A tornado threat also may develop in the southern
   Plains.

   ...20z Update...

   Only minor adjustments have been made to outlook areas with the 20z
   update. The main adjustments have been to trim the Marginal and
   Slight risk areas across parts of northwest OK into northwest TX.
   This is based on the current position of the cold front and where
   persistent precipitation/cloud cover has limited destabilization.
   The Slight risk also was expanded across parts of western KY where
   an ongoing threat for damaging winds will continue the next several
   hours. The Marginal risk has also be adjusted slightly southward
   from MO into OH based on frontal position. Minor adjustments were
   also made to the Enhanced risk/30% SIG Hail area in southwest TX
   based on current position of developing convection. Otherwise,
   overall forecast philosophy remains unchanged from the previous
   outlook.

   ..Leitman.. 04/28/2021

   .PREV DISCUSSION... /ISSUED 1131 AM CDT Wed Apr 28 2021/

   ...TX...
   An upper low is over southeast AZ today, with strong southwesterly
   midlevel winds extending across the southern Plains.  At the surface
   widespread moist and at least moderately unstable air is present
   across much of central/east TX.  Forecast soundings suggest the cap
   is relatively weak today, which makes the timing/position of
   convective initiation more uncertain.  However, it appears the
   primary forcing boundaries will be a remnant outflow boundary
   extending from north of SJT to near MWL, and also the dryline west
   of SJT.  Both boundaries are likely to activate by mid/late
   afternoon, with a risk of supercells capable of very large hail,
   damaging winds.  While low-level shear is not particularly strong,
   presence of boundaries, ample CAPE, and discrete mode may promote a
   risk of a few tornadoes across the ENH risk area through the
   evening.  

   ...West TX into OK...
   Visible satellite imagery shows breaks in the clouds across much of
   west TX into western OK. This overlaps the dryline from SJT
   northward, where most 12z CAM solutions indicate the development of
   scattered afternoon and evening thunderstorms.  A few intense cells
   are likely to form in this area, with a primary risk of large hail.

   ...Southern MO into Southern IL...
   A cluster of organized/intense thunderstorms is affecting southern
   MO this morning.  This activity may persist through the day and
   eventually track into southern IL/western KY.  Shear is quite
   strong, but instability is very limited in this corridor due to
   cloud cover.  Nevertheless, persistent convective organization may
   allow for a continued risk of damaging wind gusts and occasional
   tornado spin-ups through the day.

   ...OH/PA/NY...
   A line of showers and thunderstorms is forecast to develop this
   afternoon over Lake Erie and spread southeastward across the region.
    Dewpoints in the mid 50s and relatively strong heating will result
   in MLCAPE values around 1000 J/kg.  Deep-layer vertical shear is
   more than sufficient for a few rotating/bowing segments through the
   afternoon posing a risk of hail.  Low-level lapse rates will also be
   steep in areas where heating is optimized, aiding in the development
   of strong/damaging wind gusts.

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