Thunderstorms are starting to intensify across the Serranias del Burro mountains in northern Mexico (west/southwest of Del Rio). These storms are expected to move into the Edwards Plateau and southern Hill Country later tonight. Some of these storms will be severe with a risk of very large hail and localized damaging wind gusts. As time goes on and they get further east, the threat for a few tornadoes will increase. This will be a nocturnal threat – and continue well into the morning hours Sunday. This will be the ‘beginning’ of what should be a significant severe weather threat into Sunday.
Mesoscale Discussion 0396 NWS Storm Prediction Center Norman OK 1006 PM CDT Sat Apr 01 2017 Areas affected...Portions of the Edwards Plateau and the Texas Hill Country Concerning...Severe potential...Watch likely Valid 020306Z - 020500Z Probability of Watch Issuance...80 percent SUMMARY...Thunderstorms will increase in coverage across southwest Texas late this evening, before eventually spreading east/northeast towards morning. Initially, large hail and damaging winds will be the primary threat. However, a threat for a couple tornadoes will likely materialize overnight as storms develop east. Watch issuance is likely within the next couple of hours. DISCUSSION...Convection has once again blossomed over the Serranias del Burro mountains late this evening, likely in response to amplifying large-scale ascent related to a strengthening upper level jet. It is uncertain whether these cells are the beginning of a more organized expansion of convection through the overnight hours. However, as a southeasterly low-level jet and related moist/warm advection intensify over the next several hours, confidence is high that more widespread thunderstorm activity will develop near the Rio Grande ahead of a cold front to the northwest. Initially, this activity will interact with surface dew points in the upper 50s to near 60. Combined with steep mid-level lapse rates and ample effective shear (both observed in the 00Z DRT sounding), these cells will be capable of large hail and damaging winds. Through the early overnight however, low-level moisture will surge westward as surface-to-850mb east/southeasterly flow intensifies. Surface observations depict dew points in the mid/upper 60s over south-central Texas, and this greater moisture should advance westward quickly. Therefore, cells will evolve eastward into an environment characterized by 2000+ J/kg of MLCAPE. Combined with notable low-level speed shear and some veering with height, a threat for a couple tornadoes should gradually increase through the night, especially with eastward extent. Therefore, despite the uncertainty regarding timing of the organized severe threat, a watch will be likely within the next couple hours.