Sam Stein talks with Washington Post meteorologist Matthew Cappucci to break down the tragic flash floods that swept through central Texas and find out what made them so deadly.

Cappucci explains how a nearly invisible system of triggers, moisture from Tropical Storm Barry, and stagnant storm cells led to a catastrophic rise in river levels from 3 feet to 34 feet in just 90 minutes.

They also dig into why warnings may have gone unheeded and what this event reveals about the limitations of our weather alert systems.