Upper-Level Atmospheric Disturbance Fueled Devastating Texas Floods, Experts Say

An upper-level atmospheric disturbance contributed to the storm system lingering over Texas Hill Country, John Nielsen-Gammon, a professor of meteorological sciences at Texas A&M University and the Texas state climatologist, told Julia Jacobo of ABC News.

Floodwaters inundated parts of Texas Hill Country after days of intense rainfall fueled by a stalled storm system. (Photo: Global Empowerment Mission Facebook)

The unusually strong upper-level ridge allowed the storm system to develop a clockwise circulation pattern, effectively stalling it over the region, Nielsen-Gammon said.

The disturbance then combined with a mesoscale convective vortex—a warm, low-pressure circulation—that drew moisture from the tropical air mass over the Gulf, causing the system to produce heavy rainfall across the region for several days, Marshall Shepherd, director of the Atmospheric Sciences Program at the University of Georgia and former president of the American Meteorological Society, told Jacobo.

"It's really kind of an ideal setup from a rain production standpoint," Shepherd said.

During July, abundant moisture reaches Texas through the low-level jet stream from the western Gulf of Mexico, Nielsen-Gammon said. Additional monsoonal moisture from the Pacific and cooler air masses from the north can converge to produce extreme rainfall events.

Heavy rain that began in Texas Hill Country on Tuesday continued through Wednesday and Thursday, prompting multiple flash flood warnings along waterways, including the Guadalupe and Pedernales rivers.

Rainfall totals exceeded 2 feet in some locations, Nielsen-Gammon said.