There are few sights in nature more terrifying than a powerful tornado. These violently rotating columns of air can reach from a storm cloud to the ground, and usually are visible due to condensation, as well as dust and debris that they pick up.
Many tornadoes occur in an area we know of as tornado alley, and most only last for just a few minutes and have windspeeds of 100 miles per hour (161 kilometers per hour) or less. But the most destructive tornadoes can occur outside of tornado alley and last for more than an hour, and have wind speeds of between 200 and 300 miles per hour (322 and 482 kilometers per hour), according to the National Weather Service.
As far as severe weather events go, tornadoes can be incredibly damaging; the most violent ones can lift automobiles into the air, rip homes to shreds and turn loose debris into lethal missiles.
Tornado alley is the term given to the region of the central United States that sees the most tornadoes per year and has conditions most favorable for the formation of tornadoes. That region extends from northern and central Texas and Oklahoma northward into Kansas, Nebraska and South Dakota, explains Jason Furtado, an associate professor at the University of Oklahoma School of Meteorology.
"People who live in this region are typically the most likely to experience tornadoes in a given year and should be prepared accordingly, e.g., [having] storm shelters, weather radios, evacuation plans," Furtado says via email.
The term "tornado alley" was coined back in 1952 by two Air Force weathercasters, Maj. Ernest J. Fawbush and Capt. Robert C. Miller. The two were assigned to work on forecasting tornadoes and issued the first-ever tornado warning, according to this archived article from the National Oceanic and Atmospheric Administration (NOAA) website.
Tornado Alley and Supercell Storms
To understand why tornado alley is particularly prone to tornadoes, it's necessary to know a little about the tornado development process.
"Tornado-producing storms form through both instability (warm, moist air beneath cooler, drier air) and wind shear (changing winds with height)," according to Ross Lazear, a meteorologist at the University at Albany.
The reason tornado alley experiences some of the world's largest tornado outbreaks is because of the region's proximity to warm, moist sources, like the Gulf of Mexico, as well as cold air from higher terrain to the west, Lazear says in an email.
"The combination — and layering — of these disparate airmasses results in both instability and wind shear," Lazear says.
Keeping track of how many tornadoes happen and where they occur is complicated. Detailed records of tornadoes date back only to the 1950s in the U.S., and the information gathered hasn't always been consistent, which can make it a challenge to identify long-term trends, according to the Center for Climate and Energy Solutions. It wasn't until 2007 that scientists developed the Enhanced Fujita (EF) Scale, a standard for measuring tornado damage intensity.
"The frequency of tornadoes in a region has historically been determined by aggregating on-the-ground tornado reports and sightings over a given year," Furtado explains. "These are done by a multitude of people, including citizens, government officials, trained meteorologists, etc. who report these tornadoes to local National Weather Service offices."
After a storm system or thunderstorm that has reports of tornadoes, the National Weather Service will send trained meteorologists to the areas and confirm, based on damage, whether (a) a tornado occurred and if so (b) what the rating of the tornado is (EF-0 to EF-5), Furtado says.
Tornado Alley Is Shifting
The tornado alley of the Great Plains, of course, isn't the only area that experiences tornadoes.
"Other portions of the United States outside of what is historically referred to as 'tornado alley' do experience significant, very powerful tornadoes with frequency, as well, such as the Southeastern U.S. (e.g., Arkansas, Mississippi, Alabama, Tennessee)," Lazear says. "While tornado outbreaks are possible every month of the year in the United States, they are more likely in the Southern part of tornado alley in late winter and early spring, with tornado season migrating northward into the Northern Plains by mid-summer."
But because tornadoes happen in so many places across the map, the traditional concept of tornado alley isn't universally embraced by meteorologists. Some now even reject the term. As Furtado explains, tornadoes occur when the right conditions exist, not because of the location of the thunderstorm.
"Meteorologists predict severe weather and tornadic activity based on the ingredients present (e.g., (1) warm, moist and unstable air, and (2) large changes in wind speed and direction with height), not based on a defined climatology," Furtado says.
But there are indications that the boundaries of tornado alley may be shifting. According to 2023 research by Northern Illinois University, supercell storms have taken an eastward shift targeting areas like eastern Arkansas.
"Over the past couple of decades, we have seen a clear increase in tornado frequency further eastward into the Mississippi River Valley," Furtado says. "This means that new populations are increasingly becoming vulnerable to tornadic activity. This shift has been characterized as a 'shift' in tornado alley."
This new tornado alley is often referred to as Dixie alley and it includes, roughly, Arkansas, Louisiana, Tennessee, Alabama and Georgia. Visibility here is worse, as tornadoes are often wrapped in rain or hidden by trees and hills. And there's really no specific tornado season.
But another study from Dr. Harold Brooks, a senior scientist at the National Severe Storms Laboratory in Norman, Oklahoma, found that doesn't mean tornado alley is moving east.
Why? Because the formation of tornadoes is linked with the potential for thunderstorms, and they found there are simply more chances for thunderstorms in Dixie alley today than there are around tornado alley. Why? Climate change.
While the relationship between tornadoes and climate change isn't completely understood, studies have found that conditions that produce the most severe thunderstorms from which tornadoes can form are likely to be found more often as the planet warms.
Now That's Interesting
What may have been the earliest written report of a tornado sighting in what is now the U.S. dates back to July 1643, when then-Massachusetts Gov. John Winthrop observed a sudden powerful wind that whipped up dust, lifted his meeting house and knocked down a tree that killed a nearby onlooker, according to the NOAA.
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