Environment

TORNADO_1100

Residents of Joplin, Mo., help a woman who survived in her basement after a tornado hit the city on Sunday, May 22, 2011. The tornado tore a path a mile wide and four miles long, destroying homes and businesses. (AP Photo/Mike Gullett)

TORNADO_1099

A man salvages a guitar from a severely damaged home in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses and killing at least 89 people. (AP Photo/Charlie Riedel)

TORNADO_1098

Lynn Mosley carefully steps over downed power lines on Monday, May 23, 2011, in north Minneapolis, the morning after a tornado ripped a nearly five-mile path from suburban St. Louis Park through north Minneapolis, tearing roofs off houses, toppling huge trees and power lines and knocking over rail cars in the northern suburb of Fridley. (AP Photo/The Star Tribune, Jerry Holt)

TORNADO_1097

A cross stands atop a church that was severely damaged by a tornado in Joplin, Mo., as a severe storm passes overhead on 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)

TORNADO_1095

Emergency workers wait for a medical team after finding a body in a tornado-ravaged car in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1094

Residents begin digging through the rubble of their home after it was destroyed by a tornado that 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)

TORNADO_1093

Storm clouds dwarf a farm near Lamar, Mo., as the sun sets on Sunday, May 22, 2011. A storm earlier produced a large tornado that moved through much of Joplin, Mo., damaging a hospital and hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1092

Emergency personnel assess the damage to the Academy Sports building in Joplin, Mo., following the tornado that struck the city on Sunday evening, May 22, 2011. (AP Photo/The Joplin Globe, Roger Nomer)

TORNADO_1091

An emergency worker searches a Walmart store that was severely damaged by a tornado in Joplin, Mo., on Sunday, May 22, 2011. (AP Photo/Charlie Riedel)

TORNADO_1089

Don Atteberry, 89, surveys damage at his home in Joplin, Mo., on Monday, May 23, 2011, after it was severely damaged by a tornado on Sunday. The twister killed at least 89 people. (AP Photo/Charlie Riedel)

TORNADO_1088

On Monday, May 23, 2011, Anita Stokes salvages items from her Joplin, Mo., home, which was destroyed Sunday by a tornado. The large twister moved through much of the city, damaging a hospital and hundreds of homes and businesses and killing at least 89 people. (AP Photo/Charlie Riedel)

TORNADO_1087

A rescue worker walks past debris at Joplin High School in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, severely damaging the school, a hospital, and hundreds of homes and businesses. The twister killed at least 89 people. (AP Photo/Charlie Riedel)

TORNADO_1085

A body is seen in a tornado-ravaged car while emergency workers wait for a medical team to arrive in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1084

Emergency workers wait for a medical team after finding a body in a tornado-ravaged car in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1083

** FILE ** An emergency worker searches a tornado-damaged Walmart store in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging a hospital and hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1082

On Monday, May 23, 2011, an emergency worker searches a Walmart store that was severely damaged by a tornado in Joplin, Mo., on Sunday. (AP Photo/Charlie Riedel)

TORNADO_1081

Emergency workers wait for a medical team after finding a body in a tornado-ravaged car in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging hundreds of homes and businesses. (AP Photo/Charlie Riedel)

TORNADO_1079

A destroyed helicopter lies on its side in the parking lot of the Joplin Regional Medical Center in Joplin, Mo., on Sunday, May 22, 2011. A large tornado moved through much of the city, damaging the hospital and hundreds of homes and businesses. (AP Photo/Mark Schiefelbein)

TORNADO_1077

The damaged St. John's Regional Medical Center is seen in the distance through tornado debris in Joplin, Mo., on Monday, May 23, 2011. A large tornado moved through much of the city Sunday, damaging the hospital and hundreds of homes and businesses and killing at least 89 people. (AP Photo/Charlie Riedel)

TORNADO_1075

A shelf cloud containing a thunderstorm approaches a tornado-ravaged neighborhood of Joplin, Mo., on 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)