More tornadoes are popping up east of the Mississippi

Twisters are twirling away from Tornado Alley.

From 1979 to 2017, annual tornado frequency slightly decreased over the region, which stretches across the central and southern Great Plains of the United States, a study finds. Conversely, a higher number of storms touched down in areas east of the Mississippi River over the same period, researchers report October 17 in npj Climate and Atmospheric Science.

“The great Tornado Alley is still No. 1 in terms of [overall] frequency,” says coauthor Victor Gensini, an applied climatologist at Northern Illinois University in DeKalb. But more tornadoes in communities ill-prepared to face the relatively unfamiliar storms, such as in the southeastern United States, could mean more infrastructure damage and loss of life.

Gensini and his colleague Harold Brooks, of the National Severe Storms Laboratory in Norman, Okla., analyzed weather data from across the country for the 38-year study period. The duo charted instances of ample moisture, unstable air pockets and large changes in wind in terms of direction and altitude — perfect conditions for tornadoes. But these conditions don’t always result in a twirling twister. So the team compared the weather data with anecdotal and sometimes unreliable tornado reports from the National Weather Service’s Storm Prediction Center, also in Norman, to map the twister trends.

Other research has suggested a similar change in tornado activity, finding evidence for a region dubbed “Dixie Alley” in states such as Alabama, Arkansas and Tennessee.

The cause of the shifts in storm location and frequency is still up in the air, says meteorologist William Gallus of Iowa State University in Ames. “The current data record is obviously not long enough to know if trends are due to natural causes or man-made climate change.”