Thunderstorms have developed just west of Del Rio over the last hour. Unlike farther north in the Concho Valley, these locations are already south of the warm front. That means instability and wind shear values support organized surface-based supercelluar storm modes, even at this early hour. If these thunderstorms show signs of intensfying they could become severe with a risk of very large hail, localized damaging wind gusts, and even the threat of tornadoes. A tornado watch may be needed for the Edwards Pleateau by 2-3AM if these trends continue.
Mesoscale Discussion 0312 NWS Storm Prediction Center Norman OK 1256 AM CDT Sat Apr 13 2019 Areas affected...portions of west Texas and the Rio Grande Valley Concerning...Severe potential...Watch possible Valid 130556Z - 130800Z Probability of Watch Issuance...60 percent SUMMARY...Convection across western and southern portions of the discussion area should continue to strengthen, with potential for all modes of severe. A Tornado Watch is being considered for the area. DISCUSSION...Convection continues to deepen across eastern Pecos/Terrell counties and just south of the Rio Grande near Del Rio. These storms were already demonstrating supercellular characteristics, and these trends should continue given strongly vertically veering wind profiles, strong low-level shear (30-40 kts), and moderate surface-based instability (mid-50s to low 60s F dewpoints beneath steep mid-level lapse rates and cooling aloft). Point forecast soundings indicate that any remaining cap across western/southern portions of the discussion has been mostly removed, and with continued low-level upslope against higher terrain in northern Mexico and lift associated with the approaching mid-level trough in New Mexico, convection should continue to expand over time and possibly necessitate a tornado watch across portions of the discussion area. If issued, this watch will extend north of the current position of the warm front (subjectively analyzed from near 6R6 to near JCT), with the expectation that this front should slowly migrate northward over time. Mid-level capping is a bit more pronounced in point forecast soundings in the eastern half of the discussion area (nearer San Antonio). A couple of factors suggest presence of a severe threat in these areas beyond the next 1-2 hours or so, including: 1) continued cooling aloft with approach of a mid-level wave over New Mexico and 2) convective organization, which may overcome the cap especially in instances of strong updraft rotation and/or upscale convective growth. A few of the operational CAMS indicate this potential as well. This region will also be monitored for a potential watch. ..Cook/Edwards.. 04/13/2019