In what experts call "Flash Flood Alley," the terrain reacts quickly to rainfall steep slopes, rocky ground, and narrow riverbeds leave little time for warning.

In the early hours of July 4, the only sound many of the vacationers along the banks of the Guadalupe River would have heard was pounding rain and thunder. They didn’t get any official warning of the rapidly rising waters that ultimately proved deadly to dozens of people swept away in central Texas flash floods.