A tree lies on top of a truck after a tornado struck northern Minneapolis Sunday, May 22, 2011, causing extensive property damage, killing at least one person and injuring at least 18 others. (AP Photo/Craig Lassig)

A man carries a young girl who was rescued after being trapped with her mother in their home after a tornado hit Joplin, Mo. on Sunday evening, May 22, 2011. The tornado tore a path a mile wide and four miles long destroying homes and businesses. (AP Photo/Mike Gullett)

Rescue workers in lime-green jackets search for bodies and survivors inside St. John's hospital in Joplin, Mo., Monday, May 23, 2011. The hospital was damaged by a tornado that destroyed nearly 30 percent of the city on Sunday afternoon. (AP Photo/Tulsa World, Adam Wisneski)

Residents salvage items from their home which was severely damaged by a tornado in Joplin, Mo., as a severe storm passes overhead Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital, hundreds of homes and businesses and killing at least 89 people. (AP Photo/Charlie Riedel)

A half-mile-wide tornado moves north in Canadian County after having just crossed SH-3, the Northwest Expressway, west of SH-4 moving towards Piedmont, Okla. Tuesday, May 24, 2011. (AP Photo/The Oklahoman, Paul Southerland)

Florene Renfro, 85, breaks down as she goes through her damaged home Wednesday, May 25, 2011, in Joplin , Mo. Renfro was able to save herself by hiding in a tiny linen closet and holding on to the door handle as massive tornado severely damaged her house Sunday night. "He was knocking, but I wouldn't let him in," she said of the tornado. (AP Photo/Jeff Roberson)

Shirley Waits cries as she stands in what is left of her mother's home Wednesday, May 25, 2011, in Joplin , Mo. A massive tornado moved through Joplin Sunday night leveling much of the city. (AP Photo/Jeff Roberson)

Beverly Winans hugs her daughter Debbie Surlin while salvaging items from Winans' devastated home in Joplin, Mo. Wednesday, May 25, 2011. Winans and her husband rode out the EF-5 tornado by hiding under a bed in the home. The tornado tore through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 123 people. (AP Photo/Charlie Riedel)

Ashley Clark salvages items from a family member's devastated Joplin, Mo. home Wednesday, May 25, 2011. An EF-5 tornado tore through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 122 people. (AP Photo/Charlie Riedel)

A flag files at half staff over devastated Joplin High School in Joplin, Mo. Thursday, May 26, 2011. An EF-5 tornado tore through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 125 people. (AP Photo/Charlie Riedel)

Marie Mason reacts after looking through items of a family member at a trailer park that was damaged following a severe storm in Bloomington, Ind., Thursday, May 26, 2011. Monroe County Sheriff's officer Jeff Branham is at right. Dozens of people were injured, mobile homes were flipped and roofs were torn off houses when tornadoes and thunderstorms hit Indiana, Illinois, Missouri and other states Wednesday evening. (AP Photo/Darron Cummings)

David Turner, from Waco, Tex., sorts through belongings in a house occupied by his two sisters in devastated Joplin, Mo. neighborhood Thursday, May 26, 2011. An EF-5 tornado tore through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 125 people. (AP Photo/Charlie Riedel)

A destroyed apartment complex is seen in an aerial view over Joplin, Mo. Tuesday, May 24, 2011. A tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 116 people. (AP Photo/Charlie Riedel)

A neighborhood destroyed by a powerful tornado on Sunday is seen in Joplin, Mo. Tuesday, May 24, 2011. A tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 116 people. (AP Photo/Charlie Riedel)

A line of severe storms cross the Mississippi River in Memphis, Tenn., passing by the Memphis Pyramid on Wednesday, May 25, 2011. The dark formation was reported a few minutes earlier as a tornado in West Memphis, Ark. (AP Photo/Lance Murphey)