SPC AC 120543

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1243 AM CDT Tue Oct 12 2021

   Valid 121200Z - 131200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   CENTRAL AND SOUTHERN PLAINS...

   ...SUMMARY...
   Severe thunderstorms are expected this evening/overnight across
   portions of the central and southern Plains, where an all-hazards
   severe risk is anticipated.

   ...Central/Southern Plains...

   Early-morning water-vapor imagery depicts a well-defined upper
   trough beginning to advance east across the lower CO River Valley.
   This feature will eject northeast soon as a strong 500mb speed max
   translates through the base of the trough across NM into southeast
   CO by 13/00z, then into eastern NE by the end of the period. Strong
   12hr mid-level height falls will precede this negative-tilt trough
   and large-scale forcing for ascent should overspread the High Plains
   by late afternoon. In response to this short wave, LLJ is beginning
   to strengthen across the High Plains but will shift a bit eastward
   across western OK-KS-NE-SD prior to convective initiation.

   Boundary-layer moisture has yet to move appreciably inland over the
   Coastal Plain of TX, with the leading edge of maritime-tropical air
   mass having advanced to COT-VCT (70F Td) at 05z. Water-vapor imagery
   depicts a weak disturbance over northeast Mexico ejecting northeast
   toward this region and this feature should encourage moisture to
   begin surging inland later today. Even so, higher-quality moisture
   should struggle to advance farther north than the eastern TX
   Panhandle/western OK prior to sunset; though further advection is
   expected into western KS during the evening. This delayed moisture
   return should negate more robust surface-based updrafts prior to
   sunset across the central High Plains, but severe thunderstorms will
   develop ahead of the trough during the evening as moisture surges
   north toward the lee cyclone. 

   The Mexican short wave and low-level warm advection should aid
   early-day convection from the TX Hill country, north into OK. This
   activity should stay mostly sub-severe and the primary concern will
   be thunderstorms that initiate across the High Plains, just east of
   the strongest heating after 22z. Latest HREF suggests strong forcing
   will lead to convective initiation across the central Plains first,
   then more isolated activity should develop over the eastern TX
   Panhandle just before sunset. This southern activity will develop
   within a more moist/unstable environment, supporting very large
   hail. Have added sig hail to this portion of the outlook. Otherwise,
   a few tornadoes can be expected with supercells, especially this
   evening. Then, damaging winds are likely as a squall line should
   mature along the front due to strong forcing. Convection will spread
   east of I-35 as far south as OK by the end of the period.

   ..Darrow/Dean.. 10/12/2021

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