A t least 48 people are dead in central Texas in what officials called a "mass casualty event" after devastating flash floods slammed Hill Country, with water rescues taking place along the Guadalupe River.

According to the National Weather Service, a flash flood is flooding that begins within six hours, and often in as little as three hours, of heavy

The region is also known as “Flash Flood Alley,” because of its propensity for high levels of rainfall and the runoff on thin soil.