A tornado touches down in Sean Casey's IMAX film, Tornado Alley. Courtesy of Giant Screen Films hide caption

itoggle caption Courtesy of Giant Screen Films

The confluence of the Baker and Chacabuco rivers in the remote Patagonian region of Aysen in Chile, as seen on Jan. 20, 2008. The plan to build five new hydroelectric dams in the region has sparked protests in Chile. Jorge Uzon/AP hide caption

itoggle caption Jorge Uzon/AP

Amy Womack and her daughter, Alexis Nelson, sit on the front steps of her parents' house in Cleveland, Tenn., in late April. Womack says her father urged her and 13 relatives and friends into the basement before a tornado hit; she credits him with saving their lives. Wade Payne/AP hide caption

itoggle caption Wade Payne/AP

Debbie Surlin salvages items from her parent's home in Joplin, Mo. The tornado that struck Joplin on Sunday killed at least 125 people. Charlie Riedel/AP hide caption

itoggle caption Charlie Riedel/AP

Actor Jessica Alba, accompanied by Sen. Frank Lautenberg (D-NJ), reacts when a buzzer calling for a vote goes off during a news conference on Capitol Hill Tuesday about chemical regulation. Evan Vucci/AP hide caption

itoggle caption Evan Vucci/AP

Residents of Joplin, Mo. salvage items from their home on Monday, a day after a devastating tornado struck the town. University of Oklahoma meteorologist Howie Bluestein says this could be be the last major tornado of the season, or "it could continue to be crazy." Charlie Riedel/AP hide caption

itoggle caption Charlie Riedel/AP

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

The National Guard constructed a 2-mile temporary levee around the ALON USA refinery in Krotz Springs, La., and a neighborhood on the south side of town. Jeff Brady/NPR hide caption

itoggle caption Jeff Brady/NPR