Searchers rest outside the Briarwood Elementary School after the tornado destroyed the school , Monday, May 20, 2013. (AP Photo/ The Oklahoman, David McDaniel)

Searchers rest outside the Briarwood Elementary School after the tornado destroyed the school , Monday, May 20, 2013. (AP Photo/ The Oklahoman, David McDaniel)

A tornado moves past homes in Moore, Okla. on Monday, May 20, 2013. (AP Photo/Alonzo Adams)

A tornado moves past homes in Moore, Okla. on Monday, May 20, 2013. (AP Photo/Alonzo Adams)

A woman is pulled out from under tornado debris at the Plaza Towers School in Moore, Okla., Monday, May 20, 2013. A tornado as much as a mile (1.6 kilometers) wide with winds up to 200 mph (320 kph...

A woman is pulled out from under tornado debris at the Plaza Towers School in Moore, Okla., Monday, May 20, 2013. A tornado as much as a mile (1.6 kilometers) wide with winds up to 200 mph (320 kph) roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school.(AP Photo Sue Ogrocki)

This combination of Associated Press photos shows left, a neighborhood in Moore, Okla., in ruins on Tuesday, May 4, 1999, after a tornado flattened many houses and buildings in central Oklahoma, and...

This combination of Associated Press photos shows left, a neighborhood in Moore, Okla., in ruins on Tuesday, May 4, 1999, after a tornado flattened many houses and buildings in central Oklahoma, and right, flattened houses in Moore on Monday, May 20, 2013. Monday's powerful tornado in suburban Oklahoma City loosely followed the path of a killer twister that slammed the region in May 1999. (AP Photo)

This frame grab courtesy of KFOR TV shows the aftermath of a massive tornado as much as a mile wide with winds up to 200 mph roared through the Oklahoma City suburbs Monday, May 20, 2013. (AP...

This frame grab courtesy of KFOR TV shows the aftermath of a massive tornado as much as a mile wide with winds up to 200 mph roared through the Oklahoma City suburbs Monday, May 20, 2013. (AP Photo/Courtesy KFOR TV)

This photo provided by KFOR-TV shows a house fire outside Moore, Okla., Monday, May 20, 2013. A monstrous tornado as much as a mile wide roared through the Oklahoma City suburbs Monday, flattening...

This photo provided by KFOR-TV shows a house fire outside Moore, Okla., Monday, May 20, 2013. A monstrous tornado as much as a mile wide roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/KFOR-TV)

A woman carries a child through a field near the collapsed Plaza Towers Elementary School in Moore, Okla., Monday, May 20, 2013. A tornado as much as a mile wide with winds up to 200 mph roared...

A flag flies in the debris of a mobile home after a tornado struck a mobile home park near Dale, Okla., Sunday, May 19, 2013. (AP Photo Sue Ogrocki)

A flag flies in the debris of a mobile home after a tornado struck a mobile home park near Dale, Okla., Sunday, May 19, 2013. (AP Photo Sue Ogrocki)

Moore police dig through the rubble of the Plaza Towers Elementary School following a tornado in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (.8 kilometers) wide with winds up...

Moore police dig through the rubble of the Plaza Towers Elementary School following a tornado in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (.8 kilometers) wide with winds up to 200 mph (320 kph) roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/Sue Ogrocki)

A boy is pulled from beneath a collapsed wall at the Plaza Towers Elementary School following a tornado in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (1.6 kilometer) wide...

A boy is pulled from beneath a collapsed wall at the Plaza Towers Elementary School following a tornado in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (1.6 kilometer) wide with winds up to 200 mph (320 kph) roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on the elementary school. (AP Photo Sue Ogrocki)

Rescue workers dig through the rubble of a collapsed wall at the Plaza Tower Elementary School to free trapped students in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado as much...

Rescue workers dig through the rubble of a collapsed wall at the Plaza Tower Elementary School to free trapped students in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado as much as half a mile (.8 kilometers) wide with winds up to 200 mph (320 kph) roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo Sue Ogrocki)

A child is pulled from the rubble of the Plaza Towers Elementary School in Moore, Okla., and passed along to rescuers Monday, May 20, 2013. A tornado as much as half a mile wide with winds up to 200...

A child is pulled from the rubble of the Plaza Towers Elementary School in Moore, Okla., and passed along to rescuers Monday, May 20, 2013. A tornado as much as half a mile wide with winds up to 200 mph roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo Sue Ogrocki)

This photo provided by KFOR-TV shows homes flattened outside Moore, Okla., Monday, May 20, 2013. A monstrous tornado as much as half a mile wide roared through the Oklahoma City suburbs Monday...

This photo provided by KFOR-TV shows homes flattened outside Moore, Okla., Monday, May 20, 2013. A monstrous tornado as much as half a mile wide roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/KFOR-TV)

A woman carries an injured child to a triage center near the Plaza Towers Elementary School in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (.8 kilometers) wide with winds up...

A woman carries an injured child to a triage center near the Plaza Towers Elementary School in Moore, Okla., Monday, May 20, 2013. A tornado as much as half a mile (.8 kilometers) wide with winds up to 200 mph (320 kph) roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo Sue Ogrocki)

A fire burns in the Tower Plaza Addition in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado as much as half a mile wide with winds up to 200 mph roared through the Oklahoma City...

A fire burns in the Tower Plaza Addition in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado as much as half a mile wide with winds up to 200 mph roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo Sue Ogrocki)

This aerial photo shows the remains of houses in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods...

This aerial photo shows the remains of houses in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/Steve Gooch)

Glenn Rusk hugs his neighbor Sherie Loman outside her home north of Briarwood Elementary School after a tornado moved through the area, in Moore, Okla., Monday, May 20, 2013. (AP Photo/The...

Glenn Rusk hugs his neighbor Sherie Loman outside her home north of Briarwood Elementary School after a tornado moved through the area, in Moore, Okla., Monday, May 20, 2013. (AP Photo/The Oklahoman, David McDaniel)

JoAnn Anderson sorts through the rubble of her home after a tornado on Monday, May 20, 2013 in Moore, Okla. A monstrous tornado roared through the Oklahoma City suburbs, flattening entire...

JoAnn Anderson sorts through the rubble of her home after a tornado on Monday, May 20, 2013 in Moore, Okla. A monstrous tornado roared through the Oklahoma City suburbs, flattening entire neighborhoods with winds up to 200 mph, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/The Oklahoman, Steve Sisney)

Oklahoma City firefighters check on the status of Gene Tripp as he sits in his rocking chair where his home once stood after being destroyed by a tornado that hit the area, Monday, May 20, 2013 in...

Oklahoma City firefighters check on the status of Gene Tripp as he sits in his rocking chair where his home once stood after being destroyed by a tornado that hit the area, Monday, May 20, 2013 in Oklahoma City, Okla. (AP Photo/The Oklahoman, Chris Landsberger)

Teachers carry children away from Briarwood Elementary school after a tornado destroyed the school in south Oklahoma City, Monday, May 20, 2013. A monstrous tornado roared through the Oklahoma City...

Teachers carry children away from Briarwood Elementary school after a tornado destroyed the school in south Oklahoma City, Monday, May 20, 2013. A monstrous tornado roared through the Oklahoma City suburbs, flattening entire neighborhoods with winds up to 200 mph, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/The Oklahoman, Paul Hellstern)

Two men attempt to pry open a door on this car to check for victims in a business parking lot west of I-35 south of 4th Street in Moore, on Monday, May 20, 2013.A monstrous tornado roared through...

Two men attempt to pry open a door on this car to check for victims in a business parking lot west of I-35 south of 4th Street in Moore, on Monday, May 20, 2013.A monstrous tornado roared through the Oklahoma City suburbs, flattening entire neighborhoods with winds up to 200 mph, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/The Oklahoman, Jim Beckel)

This aerial photo shows the Moore Medical center in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado roared through the Oklahoma City suburbs Monday, flattening entire...

This aerial photo shows the Moore Medical center in Moore, Okla., following a tornado Monday, May 20, 2013. A tornado roared through the Oklahoma City suburbs Monday, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/Steve Gooch)

Kay James holds her cat as she sits in her driveway after her home was destroyed by the tornado that hit the area on Monday, May 20, 2013 in Oklahoma City, Okla. (AP Photo/The Oklahoman, Chris...

Kay James holds her cat as she sits in her driveway after her home was destroyed by the tornado that hit the area on Monday, May 20, 2013 in Oklahoma City, Okla. (AP Photo/The Oklahoman, Chris Landsberger)

Workers look for victims under debris from a tornado that passed across south Oklahoma City, Monday, May 20, 2013. A monstrous tornado roared through the Oklahoma City suburbs, flattening entire...

Workers look for victims under debris from a tornado that passed across south Oklahoma City, Monday, May 20, 2013. A monstrous tornado roared through the Oklahoma City suburbs, flattening entire neighborhoods with winds up to 200 mph, setting buildings on fire and landing a direct blow on an elementary school. (AP Photo/The Oklahoman, Paul Hellstern)