Mesoscale Discussion 1845
   NWS Storm Prediction Center Norman OK
   0146 PM CST Sun Dec 13 2020

   Areas affected...Coastal southeast Texas and southwest Louisiana

   Concerning...Severe potential...Watch unlikely 

   Valid 131946Z - 132145Z

   Probability of Watch Issuance...20 percent

   SUMMARY...Developing thunderstorms may intensify enough to support
   an isolated wind threat through the late afternoon hours for the
   coastal regions of southeast Texas and into southwest Louisiana.
   Given the dynamic environment, a brief tornado threat may manifest
   with the strongest storms.

   DISCUSSION...Recent satellite and radar imagery from the TX/LA Gulf
   Coastal areas shows convection developing along a pre-frontal
   confluence zone and gradually moving to the east/northeast. These
   storms will continue to move into a gradually expanding warm sector
   as a surface warm front continues to slowly mix northward. While
   adequate boundary-layer moisture is in place (dewpoints in the upper
   60s noted at several stations), the lack of lightning with most
   convective structures suggests that updraft intensity is rather
   weak, possibly due to poor mid-level lapse rates. Widespread cloud
   cover with minimal breaks/clearings is also inhibiting more robust
   destabilization in the near term.

   However, recent RAP mesoanalysis suggests that 500-1000 J/kg MLCAPE
   is in place along the TX coast (though this may be an
   over-estimation), and recent guidance continues to show favorable
   instability spreading eastward with the expansion of the warm
   sector. Effective bulk shear values on the order of 40-50 knots and
   effective SRH values near 200 m2/s2 across the region introduce a
   conditional threat for severe convection if sufficient
   destabilization can take place through the remainder of the
   afternoon. Any storm that can intensify and become more organized
   may pose a severe wind, as well as a brief tornado, threat. This
   threat may persist into the late afternoon and evening as the cold
   front moves into the region and provides stronger forcing for
   ascent. However, deep-layer winds more parallel to the front will
   likely promote linear storm modes and limited instability with
   eastward extent cast uncertainty into the severe potential.

   ..Moore/Dial.. 12/13/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...LCH...HGX...CRP...

   LAT...LON   28819674 29279628 30009565 30709524 30929450 30839268
               30119231 29489271 29589346 29349450 28859511 28529566
               28339619 28379653 28819674