Extreme Weather Toolkit: Severe Weather

CM: Billion-Dollar Severe Storms 2023 (EN)

As our climate continues to warm, certain conditions favorable to thunderstorms and tornadoes are occurring more often and severe weather activity is expanding into historically less-active seasons and regions.

Severe storms are thunderstorms that produce tornadoes, damaging winds (58 mph or higher), and/or hail at least one inch in diameter. 

Severe storms cause 200 deaths annually in the U.S. and account for nearly half of all billion-dollar weather disasters that have impacted the nation since 1980.

Every U.S. region faces severe weather risks—but especially in the Great Plains from April to July. People living in mobile homes are particularly vulnerable during high wind events.

Severe storms are localized, short-lived events with limited historical records. The complexity of these events makes it difficult to directly link their occurrence to global climate change. The relationship between severe storms and climate change is an active area of research.

Here’s what we do know:

More frequent and costly billion-dollar severe storms. The U.S. experienced nearly six times more billion-dollar severe storms during 2001–2022 (142 events) than during the previous two decades (25 events from 1980–2000). The average annual cost (CPI-adjusted) of billon-dollar severe storms rose from $2.5 billion (1980–2000) to $15.6 billion (2001–2022).

Tornado Trends. The number of tornadoes each year hasn’t changed since 1970 (when excluding the weakest events). But tornado variability has increased, concentrated in fewer outbreaks of larger magnitude. And tornado frequency has shifted eastward since 1979, with increased tornadic activity observed in the South, Southeast, and Ohio Valley. There’s no clear connection between these observed trends and climate change, however.

Future Potential. Severe storms are more likely to form under certain conditions—including high wind shear and convective available potential energy (CAPE). Since 1979, parts of the eastern U.S. have seen up to 15 more days with high CAPE during spring and summer—prime time for thunderstorms.

Studies suggest that conditions favorable to severe thunderstorms will become more frequent with warming over the 21st century—about 5-20% more frequent per 1.8°F of warming. Whether these changing conditions will ultimately result in the formation of more severe storms remains an active area of research. 

A 2023 study projects a 6.6% increase in supercell frequency nationwide—and especially in the densely-populated eastern U.S.—by the end of the century as a result of climate warming. 

Updated: July 2023


These resources explore the science, trends, and local impacts of severe weather in the U.S.

Search our resource library