A damaged sign lies outside the wreckage of Plaza Towers Elementary School, where seven children were killed when a tornado hit Moore, Oklahoma, in May 2013. (AP Photo/Charlie Riedel) A decade ago, two powerful tornadoes went down in the history books, serving as a deadly reminder of how violent Tornado Alley can become and how quickly. Next month will mark the 10-year anniversary of the pair of tornadoes that tore through Oklahoma. On May 20, 2013, a massive tornado rated at EF5 strength on the