Flash Flood in Aransas County, Texas

Delayed report of water covering Highway 35.

A persistent and highly moisture-laden tropical pattern set the stage for the flash flooding event from June 19-21. Thunderstorms initially developed along the Sierra Madre Oriental and crossed into South Texas on June 19, encountering an environment characterized by extremely high precipitable water values of 2.2-2.5+ inches, extreme instability with CAPE often exceeding 2,500-4,500 J/kg, and weak steering winds. As a stubborn upper-level closed low became established over South Texas, deep tropical moisture continued streaming inland on persistent southeast to east onshore flow. Multiple outflow boundaries, a mid-level vorticity maximum, and the sea breeze provided repeated lifting mechanisms for thunderstorm development. With storm motions generally under 10-15 kt and low-level inflow often stronger than the steering flow, thunderstorms repeatedly back-built, trained, and regenerated over the same locations. Rainfall rates of 2-3+ inches per hour became common, while saturated soils from prior heavy rainfall further reduced infiltration capacity. The combination of near-record atmospheric moisture, slow-moving and training thunderstorms, and several rounds of convection associated with the stationary upper low ultimately led to widespread flash flooding concerns across South Texas and the Coastal Bend through June 21.