SPC AC 251224

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0624 AM CST Thu Nov 25 2021

   Valid 251300Z - 261200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Thunderstorms are possible this Thanksgiving Day from parts of the
   Mid-South to the Texas Coast.

   ...Synopsis...
   In mid/upper levels, a positively tilted trough from Hudson Bay
   across the north-central/southwestern CONUS and northwestern MX will
   split through the period as:
   1.  The main northern-stream synoptic trough shifts eastward from
   the Plains States and upper Mississippi Valley to the lower Great
   Lakes and Appalachians, and predominantly forcing the cold front
   discussed below;
   2.  The main southern-stream component -- now apparent in moisture-
   channel imagery over AZ, northwestern Sonora and northern/central
   Baja -- digs southward slowly and develops a closed and cut-off
   500-mb low near the Baja spur.  An isolated flash or two cannot be
   ruled out north of the AZ/MX border.  However, the bulk of
   thunder-producing deep convection (in the baroclinic-leaf formation
   manifesting large-scale ascent, evident on satellite imagery east of
   the trough/low) should stay south of the border, with coverage less
   than 10% in AZ. 

   The 11Z surface analysis showed a cold front from northwestern QC
   across Lake Huron, northwestern IN, southeastern MO, the Arklatex
   region, and portions of south-central/southwest TX to eastern AZ. 
   This front should reach portions of OH, central KY, northern MS,
   central LA, and the lower Rio Grande Valley of TX by 00Z.  By 12Z
   tomorrow, the front should reach eastern NY, the Carolinas, the FL
   Panhandle, and the north-central/west-central Gulf. 

   ...Mid-South to the Texas Coast...
   Isolated to widely scattered thunderstorms are expected through this
   afternoon along and within less than 100 nm behind the cold front,
   with isolated thunderstorms still possible in the shrinking,
   weakening, prefrontal zone of low-level convergence associated with
   a warm-advection plume.  Modest magnitudes of both effective shear
   and deep-layer lapse rates suggest the severe threat is minimal, and
   too low for a categorical outlook area.  Thunderstorm coverage and
   intensity should decrease with time this afternoon and evening as
   substantial upper support remains post-frontal, and:
   1.  The western Gulf Coast part of the front interacting with the
   greatest warm-sector theta-e moves offshore;
   2.  The inland part of the front outpaces the favorably
   destabilizing warm sector and encounters progressively more
   incompletely modified return-flow trajectories.

   ..Edwards/Jewell.. 11/25/2021

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z