Extreme Weather Toolkit: Severe Weather

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

Resources

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

Search our resource library

Climate Matters

Severe Storm, Supercell, and Tornado Trends

More billion-dollar severe storms. More storms with tornadic potential. Severe weather hazards shifting east into additional vulnerable communities—and extending earlier into winter months.

Climate Matters

Changing Thunderstorm Potential

Severe weather accounts for nearly half of all billion-dollar weather disasters in the U.S. since 1980. How has one key indicator of thunderstorm severity—Convective Available Potential Energy (CAPE)—changed with recent warming?

Climate Matters

2022 U.S. Temperatures and Billion-Dollar Disasters

In 2022, the U.S. suffered 18 billion-dollar disasters and had its 18th hottest year on record.

Climate Matters

Tornado Trends

Tornado season is changing in the United States — with more tornadoes occurring in the biggest outbreaks, the tornado risk zone increasing east of the Mississippi, and more striking outside the traditional time of year.

Climate Matters

Tornadoes & Climate Change

While there are fewer days each year with tornadoes, on average, the number days with more than 30 tornadoes is increasing.

News

Tornado Days Decreasing, but Number Per Day Rising

Tornadoes are seeming to cluster together so that there are fewer days with tornadoes, but more tornadoes on the days that do have them.

Climate Matters

Local Climate Hazard Pile-Up

Unchecked greenhouse gas emissions could hit some U.S. locations with up to three severe, nearly simultaneous climate hazards by 2050 — but moderate to deep emissions cuts could significantly reduce these dangers.