National Geographic News
Photo of tornado damage in Washington, Illinois.

A neighborhood in the Devonshire subdivision of Washington, Illinois—an area not normally thought of as being part of "Tornado Alley"—is left in ruins after a tornado tore through the northern part of the town on Sunday.

Ron Johnson, Peoria Journal Star/AP

Brian Clark Howard and Ker Than

National Geographic

Published November 18, 2013

And you thought Tornado Alley was all about Kansas.

Scores of tornadoes battered the Midwest over the weekend, killing at least six people in Illinois and injuring dozens more, flattening buildings, and knocking out power for thousands.

Tornado watches were declared for swaths of Illinois, Indiana, Iowa, Michigan, Missouri, Ohio, and Wisconsin on Sunday. On Sunday evening, the National Weather Service said 77 tornadoes had been reported, mostly in Illinois, although the agency warned that some of those reports could represent multiple accounts of the same storm.

While the Great Plains states of Kansas, Nebraska, and the Dakotas, as well as parts of Texas, are collectively known as Tornado Alley for their frequent storms, the weekend was a reminder that Illinois, Indiana, Iowa, Michigan, Missouri, Ohio, and Wisconsin are also tornado-prone.

"It turns out that the [phrase Tornado Alley] isn't correct," says the Weather Channel's website. The site said that Florida actually gets more tornadoes per square mile than any other U.S. state.

Other states that also get as many or more tornadoes per square mile than the classic Tornado Alley states include Indiana, Illinois, Iowa, and Louisiana.

"If we looked at states that get more than a handful of tornadoes just about every year, then the entire area east of the Rocky Mountains—excluding New England, New Jersey, and Delaware—could be called the 'tornado strike zone,'" the Weather Channel's site added. (Related: "With Oklahoma Tornado, Questions Swirl About Climate Change Link.")

Part of the reason why Tornado Alley has received so much attention is because it occupies a unique geographic position where warm, humid air from the Gulf of Mexico; hot, dry air from Arizona and New Mexico; and cool, dry air from Canada meet, explained Christopher Karstens, a research scientist with the National Oceanic and Atmospheric Administration's (NOAA) National Severe Storms Laboratory (NSSL) in Norman, Oklahoma.

"In the springtime, those air masses tend to work together to create environments that we saw [on May 20 and May 31]," he told National Geographic earlier this year, referring to two tornado-heavy days.

"Sometimes they collide in Oklahoma, sometimes in Texas, and sometimes in Kansas."

Although tornadoes tend to occur most frequently in May and June, they can happen any month of the year, if atmospheric conditions are right.

While the United States has perhaps the best historical records for tornadoes, twisters also occur elsewhere, including in Italy, India, and South America. (Related: "Lessons From Joplin's Tornado Recovery Effort.")

Another area with conditions similar to those of Tornado Alley is Bangladesh, said Chris Weiss, an atmospheric scientist at Texas Tech University in Lubbock.

"They have a lot of violent tornadoes—some would argue even stronger [storms] and tornadoes—over there," Weiss said. "But a lot go unreported because they don't have nearly the observation network over there that we have over here."

How Tornadoes Form

While tornadoes can differ in size, strength, and location, they all share certain characteristics. They are spawned from a type of rotating storm called a supercell thunderstorm.

And they are all driven by atmospheric instability and by a phenomenon known as wind shear.

Graphic on how a tornado forms

This happens when "wind near the ground blows in one direction, but aloft it blows in another direction. This creates shear in the airflow," Karstens explained. "If you produce an updraft within that flow, the updraft will acquire the properties of the air, and the atmosphere begins to spin and rotate."

Scientists understand some of the basic conditions necessary for tornadoes to form, but many fundamental questions about tornadoes still remain unanswered.

Tim Samaras, a tornado chaser and National Geographic grantee who was killed by a twister on May 31, 2013, in El Reno, Oklahoma, said earlier in the year that we have a lot to learn about how tornadoes form.

"We still don't know why some thunderstorms create tornadoes while others don't," he said.

Tornado Forecasting

Tornadoes are much more difficult to forecast than hurricanes are. For example, the National Hurricane Center was able to predict the path of last year's Hurricane Sandy with startling accuracy a full five days before it made landfall.

In contrast, even though residents of Moore, Oklahoma, had advance warning that a potentially dangerous storm was moving in last May, they had only 16 minutes after the first warning on May 20 before the tornado touched down.

Part of the difficulty, Karstens said, is that tornadoes are much smaller than hurricanes.

"It's really a matter of scale," he explained. "With the hurricane being so large, we're able to populate our models with lots of points to resolve it and we can come up with much more accurate multiday forecasts."

In addition, while current computer models can predict when a supercell storm is likely to form, not all supercell storms give rise to tornadoes.

"That's one of the questions we're struggling with as scientists: Which storms will be the ones to go on producing tornadoes and which ones won't?" Karstens said.

Karstens is involved in an NSSL project that aims to predict a tornado's path shortly after it forms, called Warn-on-Forecast.

He's optimistic that tornado forecasting will improve as computers and tornado modeling software become more powerful, and as more environmental data such as temperature and dew-point measurements are gathered close to tornado-spawning storms by instruments and tornado researchers.

"We've got a long way to go," he said, "but I think we're making steady progress."

Jane J. Lee contributed reporting to this article.

14 comments
James Marshall
James Marshall

Science is just discovering for a fact, what many Natives people already knew. Earth is a living organism, and man, like a virus is doing his best to not only emulate the actions of a virus, but destroy his own home through irresponsible living, greed, debauchery, and other ways of destruction almost as numerous as there are people. 


We as a people cannot expect to live separate from the earth, using and partaking of things destructive to ourselves, each other and to the environment (earth) we live in, and not expect the balancing act of nature to levy a penalty against us. Penalties in the forms of Tornadoes, Super Hurricanes, Earthquakes of great magnitudes, Tsunamis of mas destruction and the list continues....  


Our irresponsibility is linked to the destruction of our homes, our families, resources, and we think it is bad now? 


This is only the beginning of what is to come. 


Unless people change their lives and attitudes, they begin to love one another, love and cherish this planet they live on, the Universal Law of balance will take over, and as in histories past, Islands fell into the sea, Continents collapsed or were divided, and new land became where once there was only water. 


If we're prepared for that kind of upheaval, then we should just keep on trucking as we are. Other wise we people need to get our acts together. We don't have that much more time...  

Chris Davis
Chris Davis

thanks geographic!!! i needed it to acually figure it out.

craig hill
craig hill

As usual, reality trumps old definitions of such approximately accurate geographic areas as "Tornado Alley". When even Mich and Wis are hit by tornadoes with such destructive force as the ones that formed in Illinois, it's more than time the concept of Tornado Alley be adjusted in everyone's mind as occurring northeast of Kansas as well as south of it.

Tornado Alley in that new sense is more like an upside down backward L in geographic shape, as an alley doesn't have to be straight but can also have a turn to it, no?

Florida doesn't quite fit the designation of a Tornado Alley all to itself inasmuch as tornadoes don't much roam the SE, but stay pretty much within Fla and don't occur too much outside it. To reassert its tornado qualities it lacks as being part of or even greater than a Tornado Alley, maybe Florida should be renicknamed The Tornado State. Would that make folks distraught for the lack of geographically accurate tornado whereabouts happier?

Elisabetta Bastai
Elisabetta Bastai

This article makes me think about what I experienced last September. I was traveling by car  from Vermont to Niagara Falls and at some point on I-90 I had to deal with the scariest thunderstorm that I had ever seen. To cut a long story short, I was really surprised to drive  into a huge cloud that looked like a supercell so far north. While I was trying to keep cool and figuring out a way out,  I couldn't help thinking about storm chasers and Samara's death. I got really lucky that that thunderstorm did not developed into a tornado...

You may read the full story  here: 

http://www.rawbubbles.blogspot.com/2013/11/cross-country-road-trip-september-2-15.html 

El Gabilon
El Gabilon

If the states mentioned are prone to tornadoes, why have these states not required builders to build tornado resistant homes and buildings? In this latest tornado hundreds of homes were torn to shreds because builders were either unaware of the story "The Three Little Pigs" or if aware didn't give a hoot or a holler.  The goal was to grab as much as they could grab regardless of the danger to prospective home owners over the years. Now we will see just how fast the INSURANCE COMPANIES pay out what home owners were insured for.  No doubt home owners will be fighing for their insurance money for years to come.  We shall also see how fast, if ever, these states require builders to meet stringent standards against wind storms.  No doubt the legislators of these states will be blowing a lot of hot wind about this situation.

Swiftright Right
Swiftright Right

Umm I was reading these articles back in the 90's and YES tornado ally pretty much does (and always has) extend up through Ill into the Bay area of Michigan

norman h.
norman h.

As long as the country most responsible for global warming, america, does nothing about it but make it worse days like this will become more and more commonplace and then not only will "hurricane alley" be redefined but so will many other areas of the country become redefined by droughts, wildfires, floods, hurricanes, etc. etc. 

David Moon
David Moon

@El Gabilon Because there's no such thing as a "tornado-resistant" home. Very structurally sound concrete structures can still be demolished or damaged to the point of being unsafe, so how could you expect to build anything else to withstand that kind of force? You can't require common people to spend the hundreds of thousands or millions of dollars required for what you are suggesting. You could possibly require tornado shelters— underground structures— to be in certain areas, but you're still talking about an extreme economic cost. You can only defend against nature to a certain point.

Janelle Hora
Janelle Hora

@Swiftright Right That was the point of the article. It states that if conditions are right, a tornado can happen anywhere. "Tornado ally" is just a term coined from the area that sees the conditions more often. Michigan's weather is a joke compared to Texas storms.  

Ryan Fisher
Ryan Fisher

@norman h.  

Global warming isn't what's causing more destructions. It's wickedness and disregard for God's laws on this promised land. We need to be better people if we want God's protection to continue. It's as simple as that. If we continue in our ways, committing adultry, fonication, lying, cheating, steeling, killing innocent babies in the womb, worshiping works of our own hands and mocking God, than we'll continue to see these disasters and many more come. Global warming isn't the problem, it us!

Jeff Price
Jeff Price

@norman h. Seriously? China doesn't bear any responsibility? Japan's rolling back of CO2 emission policies does not bear any responsibility? Volcanoes spewing out more CO2 in a day than the rest of the world combined in a year do not bear responsibility? OK. Thanks for the education.

Janelle Hora
Janelle Hora

@Ryan Fisher I didn't know the WBC was allowed to use the internet. Separation of church and state as well as church and science.

David Moon
David Moon

@Jeff Price Norman is right. While China, (and soon India) bears a huge responsibility in this, we are still the largest per capita producers of greenhouse gasses.

What's more, we are in the best economic position right now out of any country to transition to renewable energies, but we refuse to do so. China is still in their industrial revolution, and it is not fair to demand more from them than we can do, given the fact that we are an industrialized nation. We had our time of development, now it's time for us to undo some of the damage we have caused.

If we were smart, we could get to the forefront of green technology and sell to the rest of the world, including china. We have the manufacturing capabilities to do so. Instead, we're buying less efficient solar panels from China, and essentially remaining a leach when it comes to renewables.

Noti Atamelang
Noti Atamelang

Jeff,  Your first two sentences are right on!  Your third, 

"Volcanoes spewing out more CO2 in a day than the rest of the world combined in a year do not bear responsibility?"  

Is hyperbole.  Do the math.  All of us are causing climate change and only the do-gooders, (like you, me and Norman) at the bottom end show any willingness to make changes.  Billionair chateaus in Monaco and private tropical islands are immune to the mundane problems of the masses.

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