When Is Tornado Season?

If you’ve never spent a night glued to the television watching wall-to-wall tornado coverage, well, you’ve never been to Oklahoma in the springtime. Any minute you could be instructed to go to a shelter, or take cover immediately if the tornado is closing in.

Tornadoes happen fast. The most powerful can reach speeds of more than 300 miles per hour, devastating local communities that take years to rebuild.

Oklahoma has seen more than 4,000 tornadoes since 1950, the first year of National Weather Service (NWS) tracking data. But did you know that every U.S. state, even Alaska, has had tornadoes? No matter where you live, it’s important to know when you’re most at risk.

Here, storm expert Bill Bunting explains what you need to know about the timing of tornado season.

About The Expert

Bill Bunting is the deputy director of the National Oceanographic and Atmospheric Administration (NOAA) and NWS Storm Prediction Center (SPC).

Understanding Tornado Season

To get a tornado, you need a thunderstorm. A tornado is a “violently rotating column of air that extends from a thunderstorm to the ground,” according to NOAA’s National Severe Storms Laboratory definition.

For a tornado to happen, Bunting says, “the atmosphere must be unstable, and with sufficient moisture, to allow a developing thunderstorm updraft to rise vertically.”

Next, he says, you need a source of “lift,” like a cold front that makes the unstable air rise. This rising motion causes condensation to develop, leading to rainfall and sometimes hail. Next comes lightning and thunder. And if the “wind direction and speed throughout the lower portion of the atmosphere” is favorable, Bunting says, rotation follows.

At this point, Bunting says the rotating storm is known as a “supercell.” Under the right conditions, he says, “that rotation can concentrate into a tornado and accelerate wind speeds to damaging levels.”

When Is Tornado Season?

Most of the time, tornadoes occur between late March and June. But Bunting says it’s important not to focus too much on a particular season or time of year. Tornadoes touch down in winter and fall too, he says, and every month of the year has seen a tornado.

Hurricanes and tropical storms that make landfall, which often happen outside of the “typical” tornado season, can have associated inland tornadoes as well.

“In short, whenever conditions are favorable in the atmosphere the risk for tornadoes will exist,” Bunting says. He points to a tornado outbreak on December 10-11, 2021, the deadliest December for tornadoes on record. Dozens stretching from Arkansas to Kentucky killed 89 people and caused billions of dollars in damage.

In what month do most tornadoes occur?

Most tornadoes in the U.S. happen in May, according to SPC 25-year averages — about 275 in a given year. June was second with 196, and April third with 192. These are national averages, though, and shouldn’t be assumed to be the same as where you live.

If you’re in the upper Midwest, you have a later tornado peak (June) than the South, which sees more tornadoes in April on average.

Is the Timing of Tornado Season the Same Every Year?

Generally, but there is plenty of variation.

Historically, favorable tornado conditions — unstable air, thunderstorms, potential for rotation — arise each year during spring and early summer, Bunting says. “The peak tornado season tends to move north during the year … as the jet stream moves north from winter through spring and summer.” Bunting says this loop from the SPC webpage shows this in action.

“Every U.S. state has observed tornadoes,” he says, “but areas most at risk typically extend from Texas north through the central U.S. and also across the Ohio and Tennessee Valley region and the Southeastern U.S.” That’s a large chunk of the country.

Bunting says there may be variability from year to year in where most tornadoes occur, so it’s important to pay attention to local forecasts.

Predicting tornadoes based on timing or even location probabilities can be limiting, as the December 2021 tornado outbreak illustrates.

Bunting says if you look at the chances Kentucky would ever have a tornado in the second week of December, “the tornado probability is very close to zero.” Yet a tornado during that deadly outbreak was on the ground for 166 miles. Bunting says it’s one of the most devastating tornadoes in recent American history.

“This makes it a challenge to get too geographically specific about peak times of the year,” Bunting says.