Mesoscale Discussion 2045
   NWS Storm Prediction Center Norman OK
   0902 AM CST Sat Dec 18 2021

   Areas affected...Portions of southeast/coastal TX into southwestern
   LA

   Concerning...Severe potential...Watch possible 

   Valid 181502Z - 181700Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Storms may pose an increasing threat for damaging winds
   and severe hail this morning. A tornado or two may also occur. Watch
   issuance is possible.

   DISCUSSION...Linear convection is ongoing this morning along a cold
   front extending across southeast TX and into northwestern LA. A
   large degree of front-parallel flow aloft is present over this
   region, and tendency so far this morning has been for updrafts to be
   undercut by the front. Still, there appears to be some potential for
   pre-frontal storms to develop over the next couple of hours along
   one or more low-level confluence zones. One of these zones is
   already evident in radar and surface observations, extending
   southward from the front across the middle TX Coast. A rather moist
   low-level airmass exits ahead of the front, with surface dewpoints
   generally in the upper 60s to low 70s. Even with widespread
   cloudiness, modest diurnal heating and steepened mid-level lapse
   rates are already supporting MLCAPE in the 1000-1500 J/kg range
   ahead of the front. Although low-level winds are not overly strong,
   around 30-40 kt of deep-layer shear will support storm organization.

   Any convection that can develop ahead of the front will have the
   potential to become supercellular while posing both a large hail and
   damaging wind threat. It also appears possible that one or more
   small bowing line segments may accelerate ahead of the front later
   this morning and continue into the early afternoon along the TX
   Coast and perhaps into parts of southwestern LA. Damaging winds
   would be the primary threat with this activity if it occurs. A brief
   tornado or two also cannot be ruled out this morning with around
   100-150 m2/s2 of effective SRH present. However, low-level winds are
   expected to gradually diminish later this morning and into the
   afternoon as the main upper trough and stronger low-level forcing
   shifts eastward from the OH Valley across the Mid-Atlantic and
   Northeast today. Given expectations for a gradual increase in severe
   potential through the rest of the morning, watch issuance may
   eventually need to be considered for some portion of the
   middle/upper TX Coast into southwestern LA.

   ..Gleason/Kerr.. 12/18/2021

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

   ATTN...WFO...LCH...SHV...HGX...CRP...EWX...

   LAT...LON   27999678 28229773 28589794 29399785 29879765 30319690
               31199546 31179460 30909283 30499228 29939213 29449200
               29679326 29449457 28829536 28449617 27999678