Scientific American recently published a story about extreme weather that featured the research of Naresh Devineni and Niloufar Nouri of the City University of New York. This work is the result of the FY2017 Early Career Research Program award titled, “Multi-scale Modeling of Extreme Events and Impact Information” affiliated with the RGMA program area in EESM. The story was written by Mark Fischetti, Matthew Twombly, and Daniel P. Huffman.
Tornado outbreaks are moving from Texas and Oklahoma toward Tennessee and Kentucky, where people may not be prepared
Roughly 1,200 tornadoes strike the U.S. during an average year. They’re prevalent in the U.S.—far more so than anywhere else in the world—because its geography sets up the perfect conditions, especially in spring and summer. Westerly winds from the Pacific Ocean drop their moisture when they push up over the Rocky Mountains, becoming high, dry and cool as they move farther east. Similar winds may descend from Canada. Meanwhile low, warm, humid air streams northward from the Gulf of Mexico. Flat terrain along these paths allows the winds to move relatively uninterrupted, at contrasting altitudes, until they run into one another. The angles at which they collide tend to create unstable air and wind shear, two big factors that favor tornado formation. Although somewhat similar air masses do clash in other places, such as Uruguay and Bangladesh, the forces are much more powerful over the U.S. Canada ranks second worldwide with 100 twisters a year.
Although tornadoes touch down in many places across the eastern half of the country, from the 1950s through the 1990s they struck most often in Tornado Alley, an oval area centered on northeastern Texas and south-central Oklahoma. More recently, that focus has shifted eastward by 400 to 500 miles. In the past decade or so tornadoes have become prevalent in eastern Missouri and Arkansas, western Tennessee and Kentucky, and northern Mississippi and Alabama—a new region of concentrated storms.
Data gathered in the past two years show that in addition to solo storms, large tornado outbreaks—multiple twisters spawned by a single weather system—are shifting even more definitively to the east. The swarms are clustering in a tighter geographical area than in the old Tornado Alley, too. And outbreaks may be getting fiercer and more frequent. “It looks as if we may be having fewer days in the U.S. with just one tornado and more days when there are multiple tornadoes,” says Naresh Devineni, an associate professor at City University of New York, who co-led a 2021 geographical analysis of large tornado outbreaks.