Noah Stewart shelters in the closet just 15 minutes before an April 2011 tornado demolished his house. Wearing the helmet may have saved his life, one doctor says. Courtesy of the Stewart family hide caption

itoggle caption Courtesy of the Stewart family

In Henryville, Ind., on Sunday, Janet Clark stood outside what remains of her home, which was destroyed in Friday's tornado. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images

The areas inside the red lines are where tornadoes were being reported at 11:36 a.m. ET. National Weather Service hide caption

itoggle caption National Weather Service

A cross stood atop a church that was severely damaged by a tornado Sunday in Joplin, Mo., as a severe storm passed overhead earlier today (May 23, 2011). Charlie Riedel/AP hide caption

itoggle caption Charlie Riedel/AP

Homeowner Marilyn Latham stood in the wreckage of her devastated home in the Alberta City community of Tuscaloosa, Ala., on Saturday (May 7, 2011). Dave Martin/AP hide caption

itoggle caption Dave Martin/AP