Tornadoes, climate change and why Dixie is the new Tornado Alley
Ernest Agee, Professor Emeritus of Atmospheric Science, Purdue University
Tornadoes tore up homes in New Orleans and its suburbs and were reported in communities from Texas to Mississippi and Alabama as severe storms swept across the South in late March 2022. We asked tornado scientist Ernest Agee to explain what causes tornadoes and how the center of U.S. tornado activity has shifted eastward from the traditional Tornado Alley in recent years.
What causes tornadoes?
Tornadoes start with thunderstorms. Think of the thunderstorm as the parent of the tornado. When atmospheric conditions favor the development of severe storms, tornadoes can form.
The recipe for a tornado requires a few important ingredients: low-level heat and moisture and cold air aloft, coupled with a favorable wind field that increases in speed with height, as well as changes in the wind direction in the lower levels.
The right combination of heat, moisture and wind can develop rotating thunderstorms capable of spinning off a tornado or a tornado family. Thunderstorms capable of spinning off tornadoes typically develop along and ahead of a frontal boundary — where warm and cold air masses meet — often accompanied above by a strong jet stream.
Why do tornado outbreaks seem to be getting more frequent and intense? Is climate change playing a role?
Forecasting tornadoes. NOAA National Severe Storms Laboratory.
What’s interesting is that despite that increase, the per capita death toll from tornadoes has actually gone down in the latter half of the past 100 years. So, as bad as these new outbreaks are, science and technology are saving lives at a faster rate than storms are killing people.
Scientists can now anticipate and forecast areas where tornadoes may develop. If you look at NOAA’s Storm Prediction Center website, you’ll see eight-day outlooks now. That’s based on scientific knowledge and technology able to target where conditions conducive to tornadoes are developing.
People also know what to do now and are more likely to get warnings, and more homes have safe rooms able to withstand a tornado. Social media also plays a big role today. A few years ago, I had a student who was on his family’s farm when he got a text warning that a tornado was coming. He and his family got to safety just before the tornado hit.
The Southeast seems to be getting a lot more severe storms. Has Tornado Alley shifted?
Oklahoma still has tornadoes, of course. But the statistical center has moved. Other research since then has found similar shifts.
Mean number of days per year with a tornado registering EF1 strength or greater within 25 miles, 1986-2015. NOAA Storm Prediction Center
We found a notable decrease in both the total number of tornadoes and days with tornadoes in the traditional Tornado Alley in the central plains. At the same time, we found an increase in tornado numbers in what’s been dubbed Dixie Alley, extending from Mississippi through Tennessee and Kentucky into southern Indiana.
In the Great Plains, drier air in the western boundary of traditional Tornado Alley probably has something to do with the fact that tornadoes are a declining risk in Oklahoma while wildfire risk is growing.
Research by other scientists suggests that the dry line between the wetter Eastern U.S. and the drier Western U.S., historically around the 100th meridian, has shifted eastward by about 140 miles since the late 1800s. The dry line can be a boundary for convection — the rising of warm air and sinking of colder air that can fuel storms.
While scientists don’t have a full picture of the role climate change may be playing, we can certainly say we live in a warmer climate, and that a warming climate provides many of the ingredients for severe storms.
Ernest Agee does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
This article is republished from The Conversation under a Creative Commons license.
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AP Photo/Charlie Riedel
In this May 25, 2011, photo, Beverly Winans hugs her daughter Debbie Surlin while salvaging items from Winans' devastated home in Joplin, Missouri. The deadliest tornado to hit the United States in the last several decades struck on May 22, 2011, leveling a miles-wide swath of Joplin and leaving 161 people dead.
AP Photo/Charlie Riedel
In this May 25, 2011, photo, Beverly Winans hugs her daughter Debbie Surlin while salvaging items from Winans' devastated home in Joplin, Missouri. The deadliest tornado to hit the United States in the last several decades struck on May 22, 2011, leveling a miles-wide swath of Joplin and leaving 161 people dead.
Tuscaloosa Fire Lt. Brian Phillips climbs a pile of rubble in search of survivors or bodies at an apartment building in Tuscaloosa, Ala., after 362 tornadoes hit the southeastern United States over three days in April 2011, killing an estimated 321 people. Alabama was the hardest hit, with a death toll of more than 250 in that state alone.
AP Photo/Dave Martin
Tuscaloosa Fire Lt. Brian Phillips climbs a pile of rubble in search of survivors or bodies at an apartment building in Tuscaloosa, Ala., after 362 tornadoes hit the southeastern United States over three days in April 2011, killing an estimated 321 people. Alabama was the hardest hit, with a death toll of more than 250 in that state alone.
New cars and trucks at a Chevrolet dealership sit under the wreckage from a tornado that hit Mountain View, Ark., on Feb. 5, 2008. The so-called Super Tuesday outbreak of 87 tornadoes in the southeastern United States killed 57 people.
AP Photo/Danny Johnston
New cars and trucks at a Chevrolet dealership sit under the wreckage from a tornado that hit Mountain View, Ark., on Feb. 5, 2008. The so-called Super Tuesday outbreak of 87 tornadoes in the southeastern United States killed 57 people.
An American flag waves from a makeshift flag pole in front of a concrete slab that once was a house in Louisville, Miss., after an April 28, 2014, tornado destroyed the house. An outbreak of dozens of tornadoes, stirred up by a powerful storm system, hit the Southeast and Midwest over a three-day period in April 2014 and killed 32 people in Iowa, Oklahoma, Arkansas, Mississippi, Alabama and Tennessee.
AP Photo/Rogelio V. Solis
An American flag waves from a makeshift flag pole in front of a concrete slab that once was a house in Louisville, Miss., after an April 28, 2014, tornado destroyed the house. An outbreak of dozens of tornadoes, stirred up by a powerful storm system, hit the Southeast and Midwest over a three-day period in April 2014 and killed 32 people in Iowa, Oklahoma, Arkansas, Mississippi, Alabama and Tennessee.
A tornado killed 24 people on May 20, 2013, in Moore, Oklahoma. The tornado had winds over 200 miles per hour, giving it the most severe rating of EF-5.
AP Photo/Alonzo Adams
A tornado killed 24 people on May 20, 2013, in Moore, Oklahoma. The tornado had winds over 200 miles per hour, giving it the most severe rating of EF-5.
This March 1925 photo shows an overturned house that was carried more than 50 feet from its foundation following a tornado in Griffen, Ind. The March 18 tornadoes that hit Missouri, Illinois and Indiana killed nearly 700 people, topping the list of the deadliest tornadoes in the United States.
AP Photo
This March 1925 photo shows an overturned house that was carried more than 50 feet from its foundation following a tornado in Griffen, Ind. The March 18 tornadoes that hit Missouri, Illinois and Indiana killed nearly 700 people, topping the list of the deadliest tornadoes in the United States.
Bolstered by heavy equipment, workers start the gigantic task of cleaning up wreckage remaining in the downtown area of Waco, Texas, in the aftermath of a May 11, 1953, tornado. It was one of the top 10 deadliest tornadoes in U.S. history, killing 114 people.
AP Photo
Bolstered by heavy equipment, workers start the gigantic task of cleaning up wreckage remaining in the downtown area of Waco, Texas, in the aftermath of a May 11, 1953, tornado. It was one of the top 10 deadliest tornadoes in U.S. history, killing 114 people.
As others stand intact, debris from destroyed mobile homes litter the Eastbrook Mobile Home Park in the aftermath of a tornado in Evansville, Ind., on Nov. 6, 2005. The tornado ripped across southwestern Indiana and northern Kentucky, causing 20 deaths, wrecking homes and knocking out power to thousands.
AP Photo/Darron Cummings
As others stand intact, debris from destroyed mobile homes litter the Eastbrook Mobile Home Park in the aftermath of a tornado in Evansville, Ind., on Nov. 6, 2005. The tornado ripped across southwestern Indiana and northern Kentucky, causing 20 deaths, wrecking homes and knocking out power to thousands.
A vehicle was dumped along highway 86 north of Racine, Mo., by a tornado that hit the area in southwest Missouri on May 10, 2008. Fourteen people were killed and hundreds injured in the tornado.
AP Photo/Mike Gullett
A vehicle was dumped along highway 86 north of Racine, Mo., by a tornado that hit the area in southwest Missouri on May 10, 2008. Fourteen people were killed and hundreds injured in the tornado.
The first floor of a house is all that remains on Sept. 8, 2008, in Parkersburg, Iowa, more than three months after a May 25 tornado that destroyed and damaged hundreds of homes in the area and left nine people dead.
AP Photo/Kevin Sanders
The first floor of a house is all that remains on Sept. 8, 2008, in Parkersburg, Iowa, more than three months after a May 25 tornado that destroyed and damaged hundreds of homes in the area and left nine people dead.
Family members and friends try to salvage what they can on Feb. 29, 2012, in Harrisburg, Ill., after a tornado destroyed their neighborhood homes. The devastating EF4 tornado claimed eight lives.
AP Photo/Seth Perlman
Family members and friends try to salvage what they can on Feb. 29, 2012, in Harrisburg, Ill., after a tornado destroyed their neighborhood homes. The devastating EF4 tornado claimed eight lives.
Three-year-old Brooklyn Hickman helps look through the rubble of her grandfather's trailer home in Lone Grove, Okla., on Feb. 11, 2009, after a tornado struck, killing eight people. Weather woes including an unusual series of February twisters were among the top Oklahoma news stories of that year.
AP Photo/Sue Ogrocki
Three-year-old Brooklyn Hickman helps look through the rubble of her grandfather's trailer home in Lone Grove, Okla., on Feb. 11, 2009, after a tornado struck, killing eight people. Weather woes including an unusual series of February twisters were among the top Oklahoma news stories of that year.
Downed traffic lights are seen after an EF3 tornado struck on April 28, 2011, in Glade Spring, Va. Three people were killed, and several homes and truck stops along I-81 were severely damaged.
AP Photo/Jeff Gentner
Downed traffic lights are seen after an EF3 tornado struck on April 28, 2011, in Glade Spring, Va. Three people were killed, and several homes and truck stops along I-81 were severely damaged.
As dawn broke on June 8, 1984, rescuers got their first view of a destroyed Barneveld in Wisconsin. An F5 tornado ripped through the village, killing nine people and destroying most of the small community. The powerful tornado had winds over 300 mph.
Wisconsin State Journal photo
As dawn broke on June 8, 1984, rescuers got their first view of a destroyed Barneveld in Wisconsin. An F5 tornado ripped through the village, killing nine people and destroying most of the small community. The powerful tornado had winds over 300 mph.
Photos of destruction from the 1955 tornado that destroyed Udall, Kan., are displayed in the town's museum. The May 1955 tornado is among the top 25 deadliest in U.S. history, killing 80 people.
AP Photo/Charlie Riedel
Photos of destruction from the 1955 tornado that destroyed Udall, Kan., are displayed in the town's museum. The May 1955 tornado is among the top 25 deadliest in U.S. history, killing 80 people.
People clear debris from a farm field on the outskirts of Marysville, Ind., after a tornado with 150 mph winds raked through the southern Indiana hamlet on March 2, 2012. The storm was part of a tornado outbreak that left 13 people dead in southern Indiana.
AP Photo/Charles Wilson
People clear debris from a farm field on the outskirts of Marysville, Ind., after a tornado with 150 mph winds raked through the southern Indiana hamlet on March 2, 2012. The storm was part of a tornado outbreak that left 13 people dead in southern Indiana.
Several buildings sit damaged Oct. 5, 2013, in Wayne, Neb., after a deadly storm system that buried parts of Wyoming and South Dakota in heavy, wet snow also brought powerful thunderstorms packing tornadoes to the Great Plains, causing millions of dollars in damage. Some of the greatest damage from tornadoes was in Wayne, a town of 9,600.
AP Photo/Dave Weaver
Several buildings sit damaged Oct. 5, 2013, in Wayne, Neb., after a deadly storm system that buried parts of Wyoming and South Dakota in heavy, wet snow also brought powerful thunderstorms packing tornadoes to the Great Plains, causing millions of dollars in damage. Some of the greatest damage from tornadoes was in Wayne, a town of 9,600.
Steve Jones lifts his grandfather's headstone into place at the Stockton City Cemetery in Stockton, Mo., after most of the headstones and nearly all the trees in the cemetery were knocked over by a May 4, 2003, tornado that killed five people.
AP Photo/John S. Stewart
Steve Jones lifts his grandfather's headstone into place at the Stockton City Cemetery in Stockton, Mo., after most of the headstones and nearly all the trees in the cemetery were knocked over by a May 4, 2003, tornado that killed five people.
Remains of a ranger's house can be seen after a tornado ripped through the Little Sioux Scout Ranch in the remote Loess Hills, Iowa, on June 11, 2008. The EF3 tornado killed four people.
AP Photo/Loren Sawyer - Onawa Sentinel
Remains of a ranger's house can be seen after a tornado ripped through the Little Sioux Scout Ranch in the remote Loess Hills, Iowa, on June 11, 2008. The EF3 tornado killed four people.
People sort through debris of a destroyed house after a July 8, 2014, storm, in Smithfield, N.Y. The National Weather Service confirmed that a tornado destroyed homes in upstate New York where four people were killed.
AP Photo/Mike Groll
People sort through debris of a destroyed house after a July 8, 2014, storm, in Smithfield, N.Y. The National Weather Service confirmed that a tornado destroyed homes in upstate New York where four people were killed.
Tornadoes, climate change and why Dixie is the new Tornado Alley
AP Photo/Mark Humphrey
An overturned tree sits in front of a tornado-damaged home Dec. 11, 2021, in Mayfield, Ky. On Dec. 10-11, violent and rare December tornadoes ripped across Kentucky and several other states. Kentucky’s death toll alone from the storms is now 80. All together, the storms killed more than 90 people in five states. The National Weather Service recorded at least 41 tornadoes on Dec. 10 and 11, including 16 in Tennessee and eight in Kentucky. According to the National Oceanic and Atmospheric Administration, eight states — Kentucky, Arkansas, Tennessee, Missouri, Illinois, Georgia, Ohio and Indiana — reported tornadoes.
AP Photo/Mark Humphrey
An overturned tree sits in front of a tornado-damaged home Dec. 11, 2021, in Mayfield, Ky. On Dec. 10-11, violent and rare December tornadoes ripped across Kentucky and several other states. Kentucky’s death toll alone from the storms is now 80. All together, the storms killed more than 90 people in five states. The National Weather Service recorded at least 41 tornadoes on Dec. 10 and 11, including 16 in Tennessee and eight in Kentucky. According to the National Oceanic and Atmospheric Administration, eight states — Kentucky, Arkansas, Tennessee, Missouri, Illinois, Georgia, Ohio and Indiana — reported tornadoes.
Mean number of days per year with a tornado registering EF1 strength or greater within 25 miles, 1986-2015. NOAA Storm Prediction Center