A fire burns in the Tower Plaza Addition in Moore, Oklahoma, following a tornado, on May 20, 2013. #

This aerial photo shows the remains of homes hit by a massive tornado in Moore, Oklahoma, on May 20, 2013. #

An aerial photo of a neighborhood hit by a massive tornado in Moore, on May 20, 2013. #

An aerial photo of homes hit by the tornado in Moore, Oklahoma, on May 20, 2013. #

Rescue workers dig through the rubble of a collapsed wall at the Plaza Tower Elementary School to free trapped students in Moore, on May 20, 2013. #

A child is pulled from the rubble of the Plaza Towers Elementary School in Moore, and passed along to rescuers, on May 20, 2013. #

A child is carried from the rubble of the Plaza Towers Elementary School, on May 20, 2013. #

A boy is pulled from beneath a collapsed wall at the Plaza Towers Elementary School, on May 20, 2013. #

A woman is pulled out from under tornado debris at the Plaza Towers School in Moore, Oklahoma, on May 20, 2013. #

A woman walks through what remains of a bowling alley, and other buildings, after a huge tornado struck Moore, near Oklahoma City, on May 20, 2013. #

A dead dog lies covered in the driveway of a home after a tornado struck Moore, on May 20, 2013. #

People walk through a damaged area near the Moore Warren Theater after a powerful tornado ripped through the area on May 20, 2013. #

Piles of debris and mangled trees remain after a powerful tornado ripped through the area, on May 20, 2013. #

Flipped vehicles are piled up outside the heavily damaged Moore Medical Center on May 20, 2013. #

A girl tries to keep warm near the Moore Hospital after a tornado that destroyed buildings and overturned cars, on May 20, 2013. #

This aerial photo shows the remains of homes, after being flattened by a massive tornado in Moore, Oklahoma, on May 20, 2013. #

A battered, muddy vehicle destroyed by a huge tornado sits on a street in Moore, on May 20, 2013. #

People look at the damage in the parking lot of Moore Hospital after a tornado struck Moore, on May 20, 2013. #

The hood of car is wedged into the front window of the Moore Medical Center after a powerful tornado ripped through the area on May 20, 2013. #

A church steeple lies on the ground after it was toppled by a huge tornado which struck near Oklahoma City, on May 20, 2013. #

An aerial photo of a section of Moore struck by the massive tornado on May 20, 2013. #

An aerial photo of a neighborhood in Moore destroyed by the massive tornado on May 20, 2013. #

A man and two children walk through debris after a huge tornado struck Moore, on May 20, 2013. #

A vehicle lies upside down in the road after a powerful tornado ripped through the area on May 20, 2013 in Moore, Oklahoma. #

Carlos and Kim Caudillo stand in the debris of their home after a powerful tornado ripped through Moore, Oklahoma on May 20, 2013. #

Sunrise, on Tuesday, May 21, 2013, an American flag blows in the wind atop the rubble of a destroyed home in Moore, Oklahoma. #

A destroyed police car sits among the debris of tornado-ravaged homes in Moore, on May 21, 2013. #

Abby Madi (left) and Peterson Zatterlee comforts Zaterlee's dog Rippy, after a tornado struck Moore, on May 20, 2013. #

A heavily-battered truck, in a field near the Moore Medical Center, background, after a tornado moves through Moore, Oklahoma, on May 20, 2013. #

Headstones stand amid debris in the Moore Cemetery after it was damaged by a tornado May 21, 2013. #

Piles of debris and cars lie around a home destroyed by a tornado in Moore, on May 21, 2013. #

Residents pass a destroyed car as they walk through a tornado-ravaged neighborhood of Moore, Oklahoma, on May 21, 2013. #