SPC AC 060549

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1249 AM CDT Tue Apr 06 2021

   Valid 071200Z - 081200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
   LOWER MISSISSIPPI VALLEY...

   ...SUMMARY...
   Scattered severe thunderstorms are possible across the lower
   Mississippi Valley with other isolated severe storms possible
   farther north over the middle Mississippi Valley.

   ...Synopsis...
   A mid-level closed low and associated trough will move from western
   KS to northern MO during the period.  Concurrently, a belt of strong
   mid-level flow will wrap cyclonically south through east of the
   larger-scale trough.  A surface low is forecast to develop northward
   from northeast KS to northern IA while a cold front pushes east over
   AR/MO as the low becomes occluded.  

   ...Lower MS Valley...
   A still-modifying reservoir of moisture over the northwestern Gulf
   Coast will stream northward into the lower MS Valley during the day.
   Isolated to scattered showers/thunderstorms are possible over parts
   of eastern OK/western AR during the morning.  Storm activity will
   likely increase by the afternoon coincident with heating, as the
   airmass destabilizes, with MLCAPE ranging from 500 J/kg near the
   MO/AR border to around 1500-2000 J/kg over northern LA/east TX. 
   Forecast hodographs enlarge across AR/northern LA during the day
   assisted by a 45-kt LLJ.  However, a weakness currently depicted
   around 700 mb suggests a messy storm mode will likely evolve from
   initial cellular/mixed-mode storms.  The threat for large hail will
   likely focus over the western half of the lower MS Valley where
   mid-level lapse rates will support stronger updrafts and more
   optimal storm structures for hail growth.  The damaging-wind/tornado
   risk will seemingly concentrate from parts of AR/northern LA into
   central-northern MS where a combination of greater buoyancy, moist
   low levels, and enlarged hodographs will reside.  A larger band of
   storms will likely evolve by evening and persist overnight across
   parts of MS before encountering weaker instability towards early
   Thursday morning over western AL.  

   ...Middle MS Valley...
   Scattered showers and thunderstorms will likely continue through the
   morning across parts of MO/IA and thereby limit greater instability
   from developing over the area.  However, a rejuvenation to storms is
   expected during the afternoon near the surface low and possibly
   farther east ahead of residual decaying convection near the MS
   River.  Uncertainty largely related to instability will seemingly
   limit the overall severe threat.  Nonetheless, weak instability
   coupled with deep-layer shear sufficient for organized thunderstorms
   will conditionally support a marginal severe risk for storms during
   the day.  The activity will likely weaken by the early evening.

   ..Smith.. 04/06/2021

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