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Tornado Alley in the Plains is outdated; research shows the South is more vulnerable

A tornado supercell in Nebraska on May 26, 2013.

IAN LIVINGSTON/THE WASHINGTON POST

By MATTHEW CAPPUCCI | The Washington Post | Published: May 16, 2020

Anyone who's ever seen the movie "Twister" is aware of Tornado Alley — known for its reliable and, at times, hyperactive swarms of tornadoes that swirl across the landscape like clockwork each spring.

The term brings to mind the image strip of land stretching across Texas, Oklahoma, Kansas, Nebraska and the Dakotas. But meteorologists fear that imaginary zone may be leaving out areas at an even greater risk for damaging tornadoes.

In recent years, the South has come to prominence for its encounters with violent tornadoes. As recently as Easter weekend, an outbreak of more than 150 tornadoes wrought havoc across Mississippi, Alabama, Georgia, Tennessee and even into the Carolinas. A week later, another high-end EF4 tornado struck near the previous hardest-hit counties in Mississippi, marking the third EF4 to hit within a 15 mile radius over the course of only 7 days.

Meteorologists argue this corridor of enhanced tornado activity across the South isn't just another tornado hot spot — it's a bona fide extension of Tornado Alley. In fact, many atmospheric scientists feel that the term "Tornado Alley" is a misnomer in its entirety and fails to convey where the greatest tornado risks may lie. Some believe portions of the South are among the most vulnerable to tornadoes in the world.

April 27, 2011, is a day that will live in meteorological infamy. A morning squall line of vicious thunderstorms plowed across Mississippi and Alabama, unleashing a band of quick-hitting tornadoes and winds that knocked out power to a million. An EF3 tornado hit Cordova, Alabama — a town that would be struck hours later by an even more violent tornado. Tornadoes are rated on the 0 to 5 "EF" (Enhanced Fujita) scale.

The atmosphere reloaded that afternoon, giving rise to what's often regarded as the most prolific tornado outbreak in recorded history. Repeated rounds of violent tornadoes, including four EF5s, resulted in hundreds across Mississippi and Alabama as seemingly endless rotating supercell thunderstorms marched across the state. Some storms traveled hundreds of miles. All told, more than 350 tornadoes accompanied the days-long outbreak.

Already this year, tornadoes have struck Nashville, Birmingham, Atlanta, Chattanooga, and Charlotte 2020 to date is the deadliest year for tornadoes since 2011. Mississippi recorded its widest tornado on record.

Most of those deaths have occurred outside the traditionally regarded Tornado Alley, but well within the zone of where vicious tornadoes are common. Some experts agree it's time to abandon the term.

"To be honest, I hate the term 'Tornado Alley,' " said Steven Strader, an atmospheric scientist at Villanova University specializing in severe weather risk mitigation. He says he "hates" the term "Dixie Alley," which refers to the busy swath of tornado activity in the South, "even more."

"What people need to understand is that if you live east of the continental divide, tornadoes can affect you," said Strader.

The geographical distribution of tornadoes across the Lower 48 is a topic that has been the subject of investigation for years. One study conducted by P. Grady Dixon, a physical geographer at Fort Hays State University in Kansas, found that the Deep South is in essence just a continuation of the more traditionally recognized Tornado Alley.

"I'm of the opinion that tornado alley is an outdated, misleading concept in general," said Grady in an interview with The Post. "But I'm realistic in that I know [the term] is not going away anytime soon."

His project found that, on a basis of tornado density and path length, the most tornado-prone location in the country isn't in Oklahoma or Kansas at all — it's Smith County, Mississippi. Though Grady's paper was published in 2010, anecdotal evidence since suggests that finding is spot-on — that region of Mississippi has been close to ground zero for the country's worst twisters so far this year.

On the whole, Grady's work revealed not only that Mississippi and Louisiana average the most "tornado days" per year, but that an enormous circular swath from the Midwest and Corn Belt down through the Plains and South are one large breeding ground for tornadoes.

Save for a small downtick in tornado counts over the Missouri and Arkansas Ozarks, there's virtually nothing separating — or distinguishing — traditional Tornado Alley from the South.

"The term 'alley' is restrictive, suggests something that is spatially long and narrow so to speak," explained Grady. "We have a tornado region that's essentially the eastern 40 percent of the continental U.S.."

"Even just that paper, we've learned tons of things," continued Grady. "I don't think a gap [between the Plains and the South] exists ... maybe there's a low spot in activity in Missouri, but if you're drawing a line from central Mississippi to south central Kansas, there's no gap. Central Illinois to eastern Nebraska, there's no gap. They're connected."

To make matters worse, Grady uncovered evidence that suggests tornadoes in the South, or Dixie Alley, actually travel farther thanks to their faster speeds. Those longer paths make tornadoes more likely to cause damage in the South, especially before the mid-spring and summer months and again later in the fall.

"Storms tend to move faster during the cool season," said Grady, "I think they are actually longer [tornado] paths throughout the Deep South. Look at the speeds of some of these storms from that Easter event ... we were having some storms move at 70 mph."

Tornado are also as common — or even more frequent — in the South as they are on the Plains. "That region gets probably the greatest number of tornadoes, the Southeast," said Strader.

So why has Tornado Alley's colloquially defined loose definition never really included the South? It boils down to public perception, rooted in years of storm chasing, cinematography, and geography.

Our subliminal association of only the Plains as Tornado Alley largely predates us — originating when tornadoes began appearing on television and in print media.

"We've all seen 'The Wizard of Oz,' and we've all seen the tornado dancing in the landscape, the sepia tornado in the wheat field," said Strader. "We associate tornadoes [with] central half of the U.S."

It's likely a product of the imagery we see. Often, the most compelling videos of tornadoes — which routinely make the evening newscasts — come from flat landscapes with few trees to obscure the view. That's Kansas, Oklahoma, and the Texas Panhandle in a nutshell. The forests of Mississippi, Louisiana, and Alabama? Not so much.

Thunderstorms along the Gulf Coast generally form in highly humid environments, resulting in lower cloud bases that can obscure a storm's structure. Heavy rainfall frequently shrouds any tornadoes that do form, the rain-wrapped twisters impossible to photograph. Moreover, thunderstorms in the South are usually quicker-moving.

"With lower cloud levels and [faster storms], essentially they don't see the tornado coming until it's right on them," said Strader.

In addition, timing of storms may play a role. Oklahoma, for instance, sees nearly two thirds of its tornadoes during April and May, the bulk of them occurring during large outbreaks that attract media attention. While the South still sees increased activity in the spring, its accumulation of tornadoes is more spaced out over the entire year with a second season in the fall.

"Who was providing photos and videos of tornadoes? Experts and extreme enthusiasts," said Grady. "They built their [expeditions] around going to the Great Plains because of that reliable season."

"But the South [has] one really long season that runs from September to May, but they sort of get the summer off," said Grady. "Their season is less predictable. It tends to lull people to sleep. It's very inconsistent year to year."

Regardless of where the jackpot of tornadoes may form, experts agree that tornado risk ought to drive discussions on tornado safety and preparedness.

"What I like to tell people is tornado disasters are a coin," said Strader. "Tornadoes are one side of that coin, and societal influences are the other. When we're looking at tornado disasters, we don't care about tornado in middle of a field. We care about the one that goes through a subdivision. So often, we're neglecting the societal side."

Strader says that, while tornadoes routinely terrorize Oklahoma, the bull's eye for tornado risk and fatalities is located in the South. "What it comes down to is the difference in the socioeconomic structure of the two regions," he explained.

Urban sprawl, housing type, and land use all work together and culminate into a bad recipe for high-fatality tornado events in the South and Southeast. Population density is also much greater, expanding the target for tornadoes - particularly east of the Mississippi River.

The greater population density has ties to the way land is used in the Southeast, according to Strader. While the Plains is largely farmland and inhibits the spread of neighborhoods and communities, the South, albeit rural, "[doesn't] really have that strong [of an] agricultural tie anymore," said Strader.

"That allows population of South and Southeast to sprawl out a little easier," Strader explained. "When a tornado does occur in either region, odds are much greater in the [South of Southeast] of it hitting something."

In addition to the greater population density, many who live in the South reside in mobile or manufactured homes. It's no secret that mobile or manufactured homes can become death traps during tornadoes and succumb to even lower wind speeds. Contrary to popular belief, however, it's not the building's structure itself — but rather how it's anchored.

"What we have found in manufactured homes where fatalities occur is that the box, the superstructure ... that's actually built pretty well," explained Strader. "The box itself is good ... it's as good as a single family home."

The issue, he says, is with anchoring.

"Probably 95% of fatalities in manufactured homes occur because the first component of failure isn't the home itself," said Strader. "It's the anchoring to the ground."

In the aftermath of Hurricane Andrew in 1992, FEMA required mobile homes along the Gulf and Atlantic coasts to be anchored according to "zone 3" standards, which Strader believes would dramatically increase a mobile home's survivability during a tornado. He estimates anyone can bring their home up to snuff for less than a thousand dollars.

Of course, your first course of action during a tornado should be to seek shelter below ground. But some wonder why so few mobile or manufactured home communities have actual community shelters. Strader says it's not so simple.

"[Mobile and manufactured homes are] everywhere in the landscape," he said. "Everywhere else in the country, when you see a mobile or manufactured home, it's in a park. You don't have that necessarily in the Southeast. Eighty percent of mobile or manufactured homes are found in the landscape [by] themselves."

It's a construction type that is a staple of many Southern communities.

"There are counties with no mobile home parks at all, but yet sixty percent of their residents are in manufactured housing," said Strader.

That prevents the construction of community shelters; without a centralized location near to everyone, the utility of a community shelter would plummet markedly.

"In the Southeast, it's not a great solution. If everybody's twenty minutes from [a community shelter] but average warning [lead] time is twelve to thirteen minutes, they're not going to get to it," said Strader.

Putting it all together, the lack of available sheltering options — coupled with swelling population and expanding targets — has made the South the leader in tornado fatalities. Add atop that the public's tendency to delay shelter and seek visual confirmation of a tornado, most of which can't easily be spotted in the South, and you have a recipe for disaster.

In the end, Strader and Grady are optimistic that society is finally becoming aware of how outdated a concept Tornado Alley truly is. They hope that awareness of the much more widely-present tornado risk stretching from the Plains into the Midwest, South, and Southeast is on the rise.

But Strader says the South's tornado vulnerability is also on the rise, and only looks to get worse in the years ahead as urban sprawl continues. And if that happens, tornado disasters don't look to go away any time soon.

Storm chasers flock to a tornado near Bennington, Kan., in May 2013.
IAN LIVINGSTON/THE WASHINGTON POST

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