This May 21, 2013 aerial photo shows, from bottom to top, the path Monday's tornado took through Moore, Okla.

A Goodwill donation station is surrounded by debris after a powerful tornado ripped through the area on May 20, 2013 in Moore, Oklahoma.

Oklahoma National Guard soldiers and rescue workers dig through the rubble of Plaza Tower Elementary school May 21, 2013 after a devastating tornado ripped through Moore, Oklahoma on May 20.

An American flag blows in the wind at sunrise atop the rubble of a destroyed home in Moore, Okla., on May 21, 2013, a day after a tornado roared through the Oklahoma City suburb, flattening entire neighborhoods and destroying an elementary school with a direct blow as children and teachers huddled against winds up to 200 mph.

Lonnie Langston talks about his garage that was swept off the concrete pad next to his house by a tornado May 20, 2013 near Shawnee, Oklahoma. A series of tornados moved across central Oklahoma May 19, killing two people and injuring at least 21.

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 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.

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., May 20, 2013.

Dana Ulepich searches inside a room left standing at the back of her house destroyed after a powerful tornado ripped through the area on May 20, 2013 in Moore, Oklahoma. The tornado, reported to be at least EF4 strength and two miles wide, touched down in the Oklahoma City area on Monday killing at least 51 people.

People walk through a neighborhood south of SW 149th between Western and Hudson after a tornado struck south Oklahoma City and Moore, Okla., May 20, 2013.

People react in front of the Plaza Towers Elementary school in Moore following a deadly tornado, May 20, 2013.

This aerial photo shows the remains of houses in Moore, Okla., following a tornado that roared through the Oklahoma City suburbs, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school on May 20, 2013.

A nurse walks the destruction at Moore hospital after a huge tornado with winds of up to 200 miles per hour (320 kph) struck Moore, Oklahoma, near Oklahoma City, May 20, 2013.

This aerial photo shows the remains of homes hit by a massive tornado in Moore, Okla., 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.

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

A teacher hugs a child at Briarwood Elementary school after a tornado destroyed the school in south Oklahoma City, May 20, 2013.

A boy is pulled from beneath a collapsed wall at the Plaza Towers Elementary School following a tornado in Moore, Okla., May 20, 2013.

Oklahoma County Sheriff tweeted, "Widespread damage in @cityofmoore . #OKCOSO deputies are assisting."

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, May 20, 2013.

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

A woman carries her child through a field near the collapsed Plaza Towers Elementary School in Moore, Okla., 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, flattening entire neighborhoods, setting buildings on fire and landing a direct blow on an elementary school.

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

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

Overturned cars are seen after a massive tornado touched down near Oklahoma City, Okla., May 20, 2013.

This frame grab provided by KWTV shows a tornado in Oklahoma City, Okla. on April 20, 2013.

An elementary school in Oklahoma City is in ruins after a tornado hit on May 20, 2013.

This photo provided by KFOR-TV shows homes flattened outside Moore, Okla., May 20, 2013.

This photo provided by KFOR-TV shows a house fire outside Moore, Okla., May 20, 2013.

A tornado swept through Moore, Okla., May 20, 2013, causing extensive damage to an elementary school.

The funnel of a tornadic thunderstorm almost touches the ground near South Haven, in Kansas on May 19, 2013. A massive storm front swept north through the central United States on Sunday, hammering the region with fist-sized hail, blinding rain and tornadoes, including a half-mile wide twister that struck near Oklahoma City.

A tornado caused extensive damage along I-40 at the junction with US 177 on the west side of Shawnee, Okla., May 19, 2013.

Jerry Dirks, at right, hugs her friend Earlene Langley after a tornado hit Driks' home just south of Carney Okla., on May 19, 2013. Dirks was in her cellar at the time the tornado hit.

Marlena Hodson walks out of her home as her grandsons, Campbell Miller, 10, and Dillon Miller, 13, at right, help her sort through belongings after a tornado damaged her home Carney Okla., on May 19, 2013.

Johnny Ortiz, left, and James South, right, carry Miguel Morales, center, who was injured in a tornado, to an ambulance in Granbury, Texas, May 15, 2013. Officials report the tornado caused "multiple fatalities" as it tore through two neighborhoods of a North Texas town. Hood County sheriff's Lt. Kathy Jiveden reported the multiple fatalities, but she had no estimate of dead or injured.

A Texan assesses the damage to the garage of his rental home that was destroyed by a tornado in Cleburne, Texas, May 16, 2013. At least six people were killed and seven were missing after as many as 10 tornadoes ripped through north-central Texas Wednesday evening, leaving a trail of destruction from the worst severe storm outbreak in the United States so far this year.

WFAA HD Chopper 8 gets a first look at damage in Cleburne, Texas as the sun rises, May 16, 2013, after a tornado tore through the town.

WFAA HD Chopper 8 gets a first look at damage in Cleburne, Texas as the sun rises, May 16, 2013, after a tornado tore through the town.

WFAA HD Chopper 8 gets a first look at damage in Cleburne, Texas as the sun rises, May 16, 2013, after a tornado tore through the town.

WFAA HD Chopper 8 gets a first look at damage in Cleburne, Texas as the sun rises, May 16, 2013, after a tornado tore through the town.

WFAA HD Chopper 8 gets a first look at damage in Cleburne, Texas as the sun rises, May 16, 2013, after a tornado tore through the town.

A trucking company trailer landed on a car that was parked in front of a Lindsey Ln. home in Cleburne Texas after a powerful storm, May 15, 2013. Neighbors say the trailer was parked on the street and was rolled over onto the car.

A trucking company trailer landed on a car that was parked in front of a Lindsey Ln. home in Cleburne Texas after a powerful storm, May 15, 2013. Neighbors say the trailer was parked on the street and was rolled over onto the car.

The American flag is reflected on a rain drop coated windshield at a car dealership on 59 south in Houston, Texas, May 15, 2013.