NBC News | Wednesday, July 8, 2025 
How a confluence of extreme weather, geography and timing created Texas’ flood disaster

As a succession of thunderstorms fed by the remnants of Tropical Storm Barry pummeled Texas’ Hill Country, tools used by the National Oceanic and Atmospheric Administration to detect extreme rainfall began “maxing out the color charts.” The forecasting models — a flash flooding guidance system called FLASH and a program called the Multi-Radar/Multi-Sensor System that detects heavy precipitation — use a cascading series of colors to communicate the severity of rainfall and flood risk, said David Gagne, a National Center for Atmospheric Research scientist who is focused on using machine-learning to improve weather models. The floods that battered Texas’ Hill Country and have killed more than 100 people were the result of a confluence of factors related to storm dynamics and the local topography. Ultimately, they culminated in what Gagne called a “worst-case scenario.” “All the ingredients came together at the wrong place, at the wrong time, at night on a holiday weekend,” Gagne said. “This was at the top end of the scale.” While existing weather models can forecast flash flooding in advance, even the best models struggle to represent internal storm structure and to predict where, within a few miles, the hardest rainfall will strike. In this case, the off-the-charts colors on Friday morning indicated that the south fork of the Guadalupe River was taking a direct and prolonged hit. Then, instead of moving on, the storms stalled…Read more