A massive and powerful tornado hit Moore, Oklahoma this afternoon, causing widespread destruction, including at least 51 deaths. It’s the deadliest tornado since 2011, and one of the worst in the last 20 years. This evening, President Obama signed a disaster declaration for Oklahoma.

Moore has a deep and tragic tornado legacy. The town could probably lay claim to being the very center of Tornado Alley, an area roughly defined from north Texas to South Dakota, and west of the Mississippi river. On May 3, 1999, Moore was hit by one of the worst tornadoes on record. That storm’s winds were indirectly measured at 302 miles per hour, according to the National Weather Service, which called them “the highest winds ever found near earth’s surface by any means.” That tornado killed 36 people, the most deadly tornado in over 20 years, although several storms have surpassed that number of deaths since then, including 2011’s Joplin storm, which killed 158.

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