While autumn showed the largest increase in rainfall since 1950 (10 percent) largely due to tropical storms, spring and summer showed the second largest (3.5 percent). Most of the heightened spring rainfall is concentrated over the central U.S. because of more frequent intense and longer-lasting large thunderstorms, according to research. The collision of warm, moist air from the Gulf of Mexico, dry air from the Rocky Mountains, and cool, dry air from Canada causes extreme atmospheric instability and high wind shear that sustain storms for hours in the central U.S.
And research shows the extreme rains are expected to worsen, especially in the spring and Midwest. The U.S. has warmed about 2.6 degrees Fahrenheit since 1970, leading to longer heatwaves, more frequent wildfires in the West, and accelerated sea level rise. Under more warming, parts of Tennessee and Alabama, for instance, could experience 40 percent more rain in their wettest storms.
Predicting the next heavy rain
The fatal April 2025 storms across the Midwest were relatively rare, even in a warmer world—expected to occur in today’s climate about once every 90 to 240 years, analysis found. But such uncommon storms and flooding seem to be popping up more often.
(What causes flash floods? Here’s how they get so destructive so quickly)
Yet Pendergrass says it’s difficult for experts to predict where a catastrophic rain event or flash flood may happen in any given year. Climate change can boost existing weather systems, but rain events are subject to many varying factors beyond temperature—like El Niño/La Niña conditions characterized by unusual ocean surface temperatures in the tropical Pacific.