SPC AC 131958

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0158 PM CST Sun Dec 13 2020

   Valid 132000Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

   ...SUMMARY...
   A few damaging wind gusts and a couple tornadoes will remain
   possible across parts of southeast Texas and southwest Louisiana
   through the early evening.

   ...20Z Update...
   No changes have been made to the Slight Risk across parts of coastal
   southeast TX and southwest LA. A band of pre-frontal showers and
   thunderstorms should move northeastward across this area through the
   remainder of the afternoon. Any isolated damaging wind and tornado
   threat should remain focused along/near the coast, as widespread
   precipitation aided by low-level warm advection has hampered the
   northward advance of a warm front inland across southeast TX and
   southern LA. For more information on the near-term severe threat
   across this region, see Mesoscale Discussion 1845. It remains
   unclear whether sufficient destabilization will occur farther north
   into central LA and southwestern MS to support surface-based storms.
   Any strong/gusty threat across this area will likely remain marginal
   and quite isolated.

   Farther east, mid to upper 60s surface dewpoints should advance
   northward across southern AL and the western FL Panhandle late
   tonight into early Monday morning ahead of a surface low and related
   cold front moving generally eastward across the Southeast. Even
   though low-level moisture will be increasing across these areas, it
   appears that instability will be tempered by a low-level inversion
   and poor low/mid-level lapse rates. With stronger forcing for ascent
   attendant to a shortwave trough likely remaining to the north of
   this region, robust convective development late tonight may not
   occur. Have opted not to include low severe probabilities across
   southern AL and the FL Panhandle given these potentially limiting
   factors.

   ..Gleason.. 12/13/2020

   .PREV DISCUSSION... /ISSUED 1023 AM CST Sun Dec 13 2020/

   ...Southeast Texas into southwest Louisiana...

   Late this morning a warm front extends from a weak surface low in
   southeast TX, eastward to near Palacios TX and into the northwestern
   Gulf. The front will move north through the day, likely reaching the
   Houston metro early this afternoon and continuing into the southwest
   LA coastal area by late afternoon. Rich low-level moisture with
   upper 60s to 70 F dewpoints reside along and south of the warm
   front, and will contribute to MLCAPE from 800-1200 J/kg. Numerous
   showers and scattered thunderstorms are developing across southeast
   TX within corridor of isentropic ascent north of this boundary. This
   activity will remain elevated with minimal severe risk. A somewhat
   greater threat for severe storms should evolve this afternoon. Some
   CAMs suggest surface-based storms will develop along confluence
   boundaries just offshore. A couple of these storms might move inland
   and interact with the warm front where low-level hodographs with
   200-400 m2/s2 storm relative helicity and strong effective bulk
   shear will support potential for supercells capable of producing a
   tornado or two. Otherwise, additional surface based storms will be
   possible as the cold front advances southeast and interacts with the
   moist warm sector. Storms might eventually evolve into linear
   structures along the cold front this evening as they spread east
   into LA with a threat for mainly a few strong to damaging wind
   gusts. The marginal thermodynamic environment with weak lapse rates
   and widespread low clouds, along with tendency for deeper forcing
   for ascent to remain north of warm sector, could potentially serve
   as limiting factors for a more robust severe threat.

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