SPC AC 030552

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1252 AM CDT Mon May 03 2021

   Valid 031200Z - 041200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE OZARK PLATEAU EASTWARD INTO THE LOWER OHIO VALLEY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR ALABAMA
   NORTHEASTWARD INTO GEORGIA AND PARTS OF THE CAROLINAS...

   ...SUMMARY...
   Scattered severe thunderstorms are expected across parts of the
   Ozark Plateau northeastward into the Ohio Valley late this afternoon
   into tonight.  The risk for severe gusts, large hail, and tornadoes
   will accompany this activity.

   ...Synopsis...
   A mid-level trough over the OH Valley will weaken during the day as
   it moves to the central Appalachians by early evening.  The more
   notable mid-level shortwave trough will move from the Four Corners
   into the southern Great Plains, as an attendant speed max
   intensifies overnight from OK/north TX northeast into MO/AR.  In the
   low levels, a weak area of low pressure over the OH Valley will move
   into the lower Great Lakes with a wavy frontal zone extending
   southwestward into the mid MS Valley and into the southern Great
   Plains.  A large warm sector will encompass much of the Southeast
   into the OH Valley and parts of the southern Great Plains.

   ...Southern Great Plains east-northeastward into the Ozarks...
   A complex forecast is leading to above-average uncertainty for this
   forecast.  An initially capped but destabilizing boundary layer will
   feature 60s/lower 70s deg F dewpoints east of a dryline near the
   I-35 corridor in OK/north TX.  Steep 700-500 mb lapse rates (7.5 to
   8.5 deg C/km) and strong effective shear (40-50 kt) will support
   storm organization, including supercells and organized thunderstorm
   lines.  Convection-allowing models are in relatively strong
   agreement in showing simulated supercells developing during peak
   heating near the westward extension of the front over parts of
   northwest TX.  Large to very large hail will be the primary risk
   with these storms.  By late afternoon/early evening, eroding
   convective inhibition near the front may lead to isolated to
   scattered storms developing over OK with upwards of 3000 J/kg
   MLCAPE.  Strengthening low to mid-level flow during the evening will
   help facilitate upscale growth into organized severe clusters/lines
   with severe gusts/wind damage becoming a more prominent threat.  A
   couple of tornadoes and large hail are possible with the more
   intense updrafts, especially early during the convective life cycle
   of storms.  A tornado risk may persist into the overnight hours as
   storms move from OK into parts of AR/southern MO and approach the MS
   River late.

   ...Mid MS Valley into the OH Valley...
   Mid-level shortwave ridging is forecast over the lower MS Valley
   into the lower OH Valley during the day---probably precluding
   surface-based thunderstorm development.  Residual convective cloud
   debris and a possible MCV from a thunderstorm complex over the lower
   MO Valley, is expected to move east towards the MS River by early
   afternoon.  Some convection-allowing model guidance indicates
   thunderstorms will preferentially develop due to a combination of
   forcing from the front/MCV by late afternoon near the IL/MO border. 
   Upscale growth into a MCS may occur across parts of IL and
   subsequently affect the lower OH Valley after dark within a capped
   but moisture-rich/unstable airmass.  Severe, damaging gusts are the
   primary risk with this activity.  

   ...Southeast...
   The departing influence of the mid-level trough over the OH Valley
   will still maintain a belt of moderate to strong flow across the
   region during the day.  A moisture-rich airmass (surface dewpoints
   ranging from the mid 60s to near 70 deg F) will contribute to
   moderate instability developing by early afternoon (1000-2500 J/kg
   MLCAPE) with 25-40 kt effective shear.  Scattered thunderstorms are
   forecast to develop by the afternoon with large hail and damaging
   gusts being the primary threats with the stronger storms.  This
   activity is expected to weaken by early evening.

   ..Smith/Lyons.. 05/03/2021

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