SPC AC 090550

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1150 PM CST Sun Dec 08 2024

   Valid 091200Z - 101200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Thunderstorms are possible from the Lower Mississippi Valley into
   much of the Southeast States today through early Tuesday. The
   probability for severe thunderstorms appears low.

   ...Synopsis...
   A weakening shortwave trough will quickly progress eastward across
   the lower OH river valley early this morning, and is forecast to
   exit off the East Coast by afternoon. In its wake, a more amplified
   upper wave over the Rockies will continue to shift east, resulting
   in broad surface pressure falls across the Plains along and ahead of
   a southeastward migrating cold front. This low-level mass response,
   while weak, will be sufficient to maintain a southerly flow regime
   across the lower MS river valley that will continue to advect a
   warm/moist air mass inland through the next 24 hours. The persistent
   warm advection regime over the central Gulf coast will maintain
   isolated thunderstorm chances through the day. Despite 40-50 knot
   mid-level flow, weak low to mid-level lapse rates, sampled well by
   00 UTC soundings, will modulate updraft intensities and the
   propensity for organized convection for much of the day. 

   The southeastward-moving cold front is forecast to reach the lower
   MS river valley during the overnight hours tonight. Thunderstorm
   chances will likely increase between 06-12 UTC as this boundary
   impinges on a higher theta-e air mass overspreading southeast LA
   into southern MS. By this time, low-level moisture advection should
   be sufficient to mitigate the deleterious effects of nocturnal
   cooling to some degree and support surface-based convection.
   However, the overall weak synoptic ascent over the region, combined
   with limited lapse-rate advection, may not provide sufficient
   destabilization for robust deep convection despite improving
   low-level thermodynamics. Nonetheless, veering in the lowest 1-2 km
   may support weakly rotating shallow convection. Consideration was
   given for low-end tornado probabilities to address this nocturnal
   concern; however, latest CAM ensemble guidance generally shows a
   very weak convective signal (aside from the typically bullish FV3
   members), which limits confidence in the overall threat.

   ..Moore.. 12/09/2024

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