Texas Hill Country, where much of the flooding took place this time, is often referred to as “flash flood alley.” It's home to steep terrain and a lack of vegetation that creates a perfect storm for waters to rise quickly.

Search efforts continue for the dozens of people still missing after Friday's floods, as questions swirl over what went wrong. Here's what we know so far.

Flash floods happen when heavy rains unleash more water than the ground can absorb, causing that water to pile up and flow to low-lying areas