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.

At least 81 people, including more than two dozen children, died in the torrential downpour. Dozens more were still missing three days later.

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.