A young boy rests his head in his hands in front of a house which was destroyed after a tornado swept through the area the previous night in Van, Texas, on May 11. (Mike Stone/Reuters)

A tornado touches down in Cisco, Texas, on May 9. One person was killed Saturday night and another left in critical condition after the tornado hit Cisco, a rural farming and ranch area about 100 miles west of Fort Worth. (Brian Khoury via Associated Press)

Two women hug in front of the Van Intermediate School that was destroyed after a tornado touched down overnight in Van, Texas, on May 11. Multiple storms moved across the state of Texas over the weekend causing flash flooding and tornadoes. (Larry W. Smith/EPA)

A mattress from a destroyed house is tangled up in what is left of a pecan tree south of Cisco, Texas, on May 10. People in the sparsely populated ranching and farming community of Cisco were left to clean up from Saturday's tornado that left one person dead and another in critical condition. Cisco Fire Department spokesman Phillip Truitt said the two people were near each other. (Thomas Metthe/The Abilene Reporter-News via Associated )

A cowboy hat lies among the debris of destroyed homes after a tornado swept through the area the previous night in Van, Texas, on May 11. (Mike Stone/Reuters)

A tree hangs in power lines at the Bent Creek Estates subdivision following a storm in Denton, Texas, on May 10. Several Great Plains and Midwest states were in the path of severe weather, including in North Texas, where the National Weather Service said a likely tornado damaged roofs and trees near Denton. (G.J. McCarthy/The Dallas Morning News via Associated Press)

A woman walks past a fallen tree while talking on the phone after a tornado touched down overnight in Van, Texas, on May 11. Multiple storms moved across the state of Texas over the weekend causing flash flooding and tornadoes. (Larry W. Smith/EPA)

A vehicle sits damaged under downed trees on May 11 in Van, Texas. About 30 percent of the community was damaged from the storm, according to Chuck Allen, fire marshal and emergency management coordinator for Van Zandt County. (Todd Yates/Associated Press)

Ronnie Hastings looks over what used to be his grandfather's home after a deadly storm south of Cisco, Texas, on May 10. People in the sparsely populated ranching and farming community of Cisco were left to clean up from Saturday's tornado that left one person dead and another in critical condition. Cisco Fire Department spokesman Phillip Truitt said the two people were near each other. (Tommy Metthe/The Abilene Reporter-News via Associated Press)

Katie Longest photographs pink insulation in her bedroom after the roof of the home was blown off during a storm on May 7 in Bridge Creek, Okla. Communities in several southern Plains states set to work cleaning up Thursday after a night of storms that spawned dozens of tornadoes, assessing the damage under sunny skies but with the threat of even worse weather on the horizon. (Steve Sisney/The Oklahoman via Associated Press)

A man walks atop his recreational vehicle in Oklahoma City, on May 7. Gov. Mary Fallin has declared a state of emergency in 12 Oklahoma counties hit by tornadoes, severe storms, straight-line winds and flooding. (Sue Ogrocki/Associated Press)

Christie Hulsey throws out pieces of the ceiling while trying to salvage personal items in the family home that was destroyed after a tornado touched down overnight in Van, Texas, on May 11. Multiple storms moved across the state of Texas over the weekend causing flash flooding and tornadoes. (Larry W. Smith/EPA)

A man walks past a hotel that was damaged in Wednesday's storm in south Oklahoma City, on May 7. Tornadoes hit Nebraska, Kansas, Oklahoma and north Texas on Wednesday. Most were small and chewed up only farmland, but a pair crossed into Oklahoma City and damaged homes and businesses. A few injuries were reported, including about a dozen at an Oklahoma City trailer park and one woman drowned in an underground storm shelter that flooded. (Steve Gooch/The Oklahoman via Associated Press)

The driver of a pickup truck which crashed in severe weather on Interstate 35 gestures to his rescuers after being cut from the truck in Moore, Okla., on May 6. Forecasters declared a tornado emergency for Moore. (Sue Ogrocki/Associated Press)

Damon Braley holds Sammy, who belongs to Braley's parents, as he looks over the area where his parent's recreational vehicle used to park in Oklahoma City, on May 7. He said his parents were both taken to the hospital May 6th after severe weather hit the area, but Sammy was only found today. Gov. Mary Fallin has declared a state of emergency in 12 Oklahoma counties hit by tornadoes, severe storms, straight-line winds and flooding. (Sue Ogrocki/Associated Press)

Manya Hunt, 7, stands outside of her grandparents' house that suffered from tornado damage in Oklahoma City, Okla., on May 7. One person was killed and about a dozen others injured by tornadoes that touched down near Oklahoma City, part of a storm system that flattened homes and caused flooding in several Great Plains states, officials said. (Nick Oxford/Reuters)

Dillan Taylor salvages items from her destroyed recreational vehicle in Oklahoma City on May 7. Communities that were threatened by a pack of more than 50 tornadoes earlier this week shift their attention from cleaning up to getting ready for the next storm. The menacing clouds had barely vanished before forecasters warned of another system that could bring twisters through the weekend. (Sue Ogrocki/Associated Press)

A tornado passes near Halstead, Kan., on May 6. A swath of the Great Plains were under a tornado watch on May 6, including parts of North Texas, Oklahoma, Kansas and Nebraska. (Travis Heying/The Wichita Eagle via Associated Press)

David Arce (back) and Aldyn Rowan (front) hang an American flag on a destroyed tree in front of their damaged house after a tornado touched down overnight in Van, Texas, on May 11. (Larry W. Smith/EPA)