SPC AC 131247

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0647 AM CST Sun Dec 13 2020

   Valid 131300Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FAR SOUTHEAST
   TX/SOUTHWEST LA...

   ...SUMMARY...
   Damaging winds and a couple tornadoes are possible across a portion
   of southeast Texas and southwest Louisiana, mainly from
   mid-afternoon to early evening.

   ...Southeast TX to LA and southwest MS...
   Primary severe potential is expected to peak this afternoon into
   early evening. Although confidence is not high, the conditional
   threat for a couple tornadoes and damaging winds appear large enough
   to warrant a Slight Risk delineation centered on the Lower Sabine
   Valley.

   A vigorous shortwave trough over the southern High Plains will move
   east into the TN Valley by early Monday. Resultant cyclogenesis
   across the TX Gulf Coast by midday should result in gradual
   deepening of the low as it tracks from near Houston to Atlanta by
   12Z. A richly moist warm sector characterized by 68-71 F surface dew
   points was present across the northwest Gulf and the Lower TX Coast,
   supporting a plume of MLCAPE from 500-1500 J/kg, as sampled by the
   12Z Corpus Christi and Brownsville soundings. This will probably
   spread as far northeast as southwest LA.

   Initially elevated convective development should further blossom
   across east TX this morning. As forcing for ascent strengthens and
   low-level warm theta-e advection persists, convective development
   into the confined warm sector appears possible by mid-afternoon.
   Enlarged low-level hodographs coinciding with the northeast extent
   of surface-based instability should support a conditional risk for a
   couple embedded supercells with the primary hazard being a tornado,
   centered on the Lower Sabine Valley. Low-level winds are progged to
   become increasingly veered with southwest extent during the
   afternoon and a predominant cluster mode early in the convective
   life cycle should mitigate a greater tornado threat.

   During the late afternoon to early evening, a narrow squall line
   should evolve across far southeast TX into northern LA and progress
   east across most of LA into MS before weakening. Strengthening
   700-mb flow behind this line should aid in potential for isolated
   severe gusts across far southeast TX and southwest LA. Low-level
   stability will be a limiting factor with northern/eastern extent,
   but a threat for isolated damaging gusts should exist given the
   increasingly impressive kinematic profiles.

   ..Grams/Goss.. 12/13/2020

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