SPC AC 041951

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0151 PM CST Sat Dec 04 2021

   Valid 042000Z - 051200Z

   ...NO SEVERE THUNDERSTORM AREAS FORECAST...

   ...SUMMARY...
   Isolated thunderstorms are possible across a wide area from north
   Texas and southern Oklahoma, through parts of the mid South.

   ...20Z Update...
   Forecast outlined in the previous discussion (appended below) still
   remains valid. Highest thunderstorm coverage still appears to be
   over the Arklatex vicinity after 06Z. Steep mid-level lapse rates
   will be in place, fostering modest elevated instability and the
   potential for a few storms capable of marginal hail. Limited
   large-scale forcing for ascent and relatively warm mid-level
   temperatures cast some doubt to overall storm coverage, with current
   forecast coverage still expected to remain below thresholds for
   severe probabilities.

   ..Mosier.. 12/04/2021

   .PREV DISCUSSION... /ISSUED 1031 AM CST Sat Dec 04 2021/

   ...Synopsis...
   In the mid levels, a split flow regime with moderate to strong
   northwesterly flow was observed across the northern third of the
   CONUS. Several vorticity maxima and their associated jet streaks
   within the mostly zonal flow field will move east with time today,
   supporting several areas of wintry precipitation from the Pacific
   Northwest/northern Rockies into the Northeast. Within the weaker
   southern branch of the mid-level westerlies, an upper low over the
   Southwest will linger through the forecast period while a weak
   shortwave trough moves east along the Gulf Coast. At the surface, a
   stalled front and weak low from eastern Oklahoma and north Texas
   into Alabama will support increased ascent and moistening through
   the forecast period.

   ...Southern Plains and portions of the Southeast...
   As low-level moisture and weak ascent increase through the period,
   Isolated thunderstorms may develop through the forecast period
   across several areas. Weak isentropic ascent along the front through
   the Gulf coast and central Alabama may support a few thunderstorms
   as diurnal warming and moistening contribute to a weakly unstable
   (MUcape around 500 J/kg) environment.

   The greatest focus for warm and moist ascent appears likely across
   portions of north Texas and eastern Oklahoma into southern Arkansas
   late in the period, as a low-level jet and upstream shortwave trough
   support isolated thunderstorm development overnight. Continued
   low-level warm advection should result in low 60s F surface
   dewpoints reaching into southern Arkansas by 06z. Cooling
   temperatures aloft ahead of the southern branch shortwave should
   favor modest lapse rates around 6.5 C/km aiding in weak to moderate
   destabilization. With MUCAPE around 500-100 J/kg, and weak mid-level
   flow, a few pule type storms with small hail may develop. However,
   forecast coverage is expected to remain below thresholds for severe
   probabilities.

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