SPC AC 070756

   Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0156 AM CST Thu Dec 07 2023

   Valid 091200Z - 101200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EAST TX
   ACROSS THE LOWER MS VALLEY...

   ...SUMMARY...
   Scattered severe thunderstorms will be possible from east Texas
   across the Lower Mississippi Valley, mainly on Saturday afternoon
   into the early evening.

   ...Synopsis...
   The broader synoptic trends noted in D2 persist into D3 with a
   leading shortwave impulse and attendant cyclogenetic surface low
   rapidly progressing across the central Great Lakes towards James
   Bay. The trailing cold front from the Midwest to east TX will
   continue to push southeast, aided by a seasonably tight surface
   pressure gradient between it and a stout anticyclone over the
   northern Great Basin. Much weaker secondary cyclogenesis is
   generally progged from the Ark-La-Tex on Saturday morning to at
   least the TN Valley by Saturday night, as an upstream basal
   shortwave impulse shifts from the Four Corners across the southern
   Great Plains. Model spread in placement of the surface cyclone/front
   increases late in the period. 

   ...East TX to the Mid/Deep South...
   Slower timing of appreciable mid-level height falls over the warm
   sector on Saturday suggests that more than isolated thunderstorm
   development should hold off until midday through the afternoon. This
   would likely allow for a plume of moderate buoyancy characterized by
   MLCAPE of 1000-1500 J/kg to become established from the Upper TX
   Gulf Coast towards the Ark-La-Tex amid surface dew points into the
   mid to upper 60s. Deep-layer southwesterly shear vectors should be
   nearly parallel to the orientation of the cold front, supporting a
   predominant clustered to linear convective mode. As such, convection
   will likely become widespread by late afternoon into the evening
   with favorable effective bulk shear for organized updrafts. 

   Low-level shear will be modest with southwest extent where the
   larger buoyancy is expected, suggesting a predominant severe
   wind/hail threat. Enlarged low-level hodographs should generally be
   confined from the Ark-La-Miss to the northeast and east, where
   surface-based instability should be diminishing with spatial extent.
   Given the overall model trends for only weak secondary cyclogenesis
   through 12Z Sunday, the eastern extent of the 15 percent probability
   area has been held as-is. Confidence is low in just how far east the
   extent of low-probability wind/tornado threats exist overnight.

   ..Grams.. 12/07/2023

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