SPC AC 281631

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1131 AM CDT Wed Apr 28 2021

   Valid 281630Z - 291200Z

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

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
   SOUTHERN PLAINS...AND OVER THE UPPER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the southern
   Plains to southwest Texas this afternoon and 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.

   ...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.

   ..Hart/Squitieri.. 04/28/2021

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