Behind the numbers: How likely is your state to see a tornado?

By Olivia Miltner, AccuWeather staff writer

Tornadoes can be some of the most spectacular examples of severe weather in the world, and the United States reports more of them than any other country, according to the National Centers for Environmental Information (NCEI).

Tornadoes tend to develop more frequently in some regions of the U.S. during certain times of the year depending on the geography, weather patterns and specific weather conditions of an area.


An Oklahoma tornado. Oklahoma is part of Tornado Alley and sees more tornadoes than many other U.S. states. (Photo/National Severe Storms Laboratory/Flickr)

The part of the U.S. that has some of the strongest and most frequent tornadoes is known as Tornado Alley, located in the southern central U.S. Here, weather patterns tend to be favorable for tornadoes to form, AccuWeather Senior Meteorologist Guy Pearson said.

“Across the southern Plains and even into the southern U.S., you get a good mixture of moisture, which you need for severe thunderstorms to develop, including tornadoes,” Pearson said. “The interaction of your cold front and strong moisture really comes together across the Plains, into the southern Plains and even points east.”

Late spring through early summer is the most common time of the year for tornadoes to form. In the southern Plains, the time frame is usually from April to early June, while areas farther north, such as the Upper Midwest and into North Dakota, experience a slightly later tornado season because of differing weather patterns.

Pearson said tornadoes are most common in the spring because that is when cold fronts and warm, moist air tend to clash the most. This is in contrast to summer, when everything is warm, and winter, when everything is cool.

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A second, though smaller, spike in tornadoes happens in the early fall. Once again, this occurs when regions see an increase in clashes of warmer and cooler air.

Finally, the Gulf Coast states, nicknamed Dixie Alley, see a rise in tornadoes during late fall and even into December, according to the NCEI.

Although colliding air masses are important ingredients for tornadoes, they also need a lot of moisture to form, Pearson said.

Although a glance at the Storm Prediction Center’s data of recorded tornadoes shows an increase in frequency throughout the past 60 years, both the SPC and Pearson said the change can be attributed to better technology and more thorough reporting instead of increasing numbers of tornadoes.

“Technology nowadays makes it much easier for one, meteorologists to be able to see things but then two, the chasers, the storms spotters, there’s a lot more people out there actually looking for tornadoes,” Pearson said, noting many areas that see the most tornadoes have also become more populated.

One major technological change that has helped meteorologists better see inside storms occurred when the National Oceanic and Atmospheric Administration implemented duo-polarization across its radar system, which was completed in 2013.

Meteorologists looks for basic ingredients that signal an environment is capable of producing a tornado, but even if all those are present, a tornado is still not guaranteed, Pearson said. Some aspects of a storm, like its shape and wind direction, can be obvious signs of a potential tornado. However, identifying specifically where and when a tornado will form is still difficult.

"The science is not good enough yet," Pearson said.

Still, adding duo-polarization to the radars has enabled meteorologists to see tornadoes developing in instances that would not have been possible 10 years ago, Pearson said. The added insight means more warning for businesses and people who could be faced with a tornado.

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