Oklahoma is located in a region of the U.S. commonly referred to as Tornado Alley.
The National Oceanic and Atmospheric Administration has an explanation for why so many big tornadoes hit this portion of the Midwest. The region is in an ideal spot for "supercell thunderstorms," which produce violent tornadoes, like the EF5 that hit Moore, Oklahoma on May 20.
Supercell thunderstorms are the most violent and produce high winds and hail, according to the National Weather Service. They typically occur in the spring, which is tornado season.
The location of Tornado Alley is what makes it more prone to twisters. The Great Plains allow cold air from the Arctic to stream south as warm, humid air comes up from the Gulf of Mexico, NBC News reports. When cold air clashes with warm, moist air, supercell thunderstorms and tornadoes can form.
Moore, Oklahoma has seen several massive tornadoes in the past 15 years, leading people to wonder if the Oklahoma City suburb is a tornado magnet. Monday's tornado killed at least 24 people and destroyed hundreds of homes in the town.
It was not only the size and strength of the twister that made it deadly, but where it hit. When tornadoes form in the middle of nowhere, they can't cause a lot of damage, but when they hit towns and cities, they kill. Moore's last big tornado-related disaster — on May 3, 1999 —took a very similar path to Monday's killer twister.
But sometimes, "things like this can just happen in clusters," tornado expert and meteorologist Bob Henson told NBC News. He cites an example: in Codell, Kan., tornadoes touched down on May 20, 1916, 1917, and 1918. The last one killed 10 people. Henson calls it coincidence.
Tornado Alley isn't the only place in the U.S. that sees violent tornadoes. USA Today points out that a deadly tornado hit western Massachusetts in 2011 and that tornadoes are more likely to touch down in "Dixie Alley" in the Southeast than in Tornado Alley.
The U.S. has an average of more than 1,000 tornadoes every year, according to the NOAA. The majority of the world's tornadoes occur in the U.S. Canada is a distant second at about 100 per year.
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