On the night the deadly floodwaters raged down the Guadalupe River in Texas, the National Weather Service forecast office in Austin/San Antonio was missing a key member of its team: the warning coordination meteorologist,

This part of Texas Hill Country is known for flash floods. Why were so many people caught off guard when the river turned violent?

A hydrologist explains why the region is known as Flash Flood Alley and how its geography and geology can lead to heavy downpours and sudden, destructive floods.

A National Weather Service advisory warned of another 2-4 inches of rain falling in the region − and isolated areas could see 9-12 inches.

More than two dozen Mexican rescue volunteers and firefighters have been looking for victims and clearing debris along the Guadalupe River. Others were left waiting for visas and humanitarian permits to cross the border.

With more than 170 still missing, communities must reconcile how to pick up the pieces around a waterway that remains both a wellspring and a looming menace.

The Texas Hill Country has been notorious for flash floods caused by the Guadalupe River. Here's why the area is called "Flash Flood Alley."