Mesoscale Discussion 1893
   NWS Storm Prediction Center Norman OK
   0710 AM CST Thu Dec 31 2020

   Areas affected...Portions of the upper TX Coast and far southwestern
   LA

   Concerning...Severe potential...Watch possible 

   Valid 311310Z - 311445Z

   Probability of Watch Issuance...60 percent

   SUMMARY...The threat for isolated tornadoes and damaging
   straight-line winds should increase this morning. Watch issuance may
   be needed.

   DISCUSSION...Convection has gradually increased in coverage this
   morning across the western Gulf of Mexico and near Matagorda Bay
   along the TX Coast, as forcing for ascent preceding an upper low
   over northern Mexico overspreads this region. As a surface low
   develops northward along/near the upper TX Coast this morning,
   thunderstorms should focus along an eastward-moving cold front.
   Although the warm sector is not forecast to make much northward
   progress across southeast TX and southwestern LA this morning, the
   presence of mid 60s surface dewpoints should support modest
   boundary-layer instability (MLCAPE 500-1000 J/kg). Both the low and
   mid-level flow fields are expected to strengthen over the next few
   hours as the upper low moves slowly northeastward, with a
   corresponding increase in effective bulk shear to 45-60 kt likely. A
   mix of supercells and short line segments should develop along/ahead
   of the front. Given the veering/strengthening low-level wind profile
   will support updraft rotation, isolated tornadoes appear possible.
   Damaging straight-line winds and marginally severe hail may also
   occur. A tornado watch may be needed for some portion of the upper
   TX Coast vicinity this morning to account for this increasing severe
   risk.

   ..Gleason/Thompson.. 12/31/2020

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

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

   LAT...LON   28589596 28909597 29449589 29949553 30359500 30629455
               30659395 30479345 30129321 29789325 29709370 29639403
               29429461 29289474 28869536 28589596