Environment

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Nebraska Gov. Dave Heineman, accompanied by Clay County EMA official Loren Uden, right, surveys damage to downtown Sutton, Neb., Monday, May 12, 2014, after a tornado touched down in town on Sunday. Several tornadoes moved across Nebraska on Sunday causing damage to homes and businesses in or near Sutton, Garland, Cordova, Beaver Crossing and Daykin. The storms also left more than 18,000 utility customers without electricity. (AP Photo/Nati Harnik)

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Volunteers clear bricks and debris from the roof of a building in Beaver Crossing, Neb., Monday, May 12, 2014. Beaver Crossing was hit hard after several tornadoes moved across Nebraska on Sunday causing damage to homes and businesses in or near Sutton, Garland, Cordova and Daykin. The storms also left more than 18,000 utility customers without electricity. (AP Photo/Nati Harnik)

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RFK Memorial Stadium is visible behind the U.S. Capitol from the 500-foot level of the Washington Monument in Washington, Monday, May 12, 2014, as it re-opens. The monument, which sustained damage from an earthquake in August 2011, reopened to the public today. (AP Photo)

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Visitors line up for tickets which are distributed at on a first-come basis at the Washington Monument in Washington, Monday, May 12, 2014, ahead of a ceremony to celebrate its re-opening. The monument, which sustained damage from an earthquake in August 2011, is reopening to the public today. (AP Photo)

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In this Sunday May 11, 2014 photo, Carlos Estrada watches a wall cloud that spawned a tornado warning northwest of Dorchester, Neb. Nebraskans are beginning to clean up debris and assess the damage this weekend's severe thunderstorms and tornadoes left behind. (AP Photo/The Omaha World-Herald, Chris Machian) MAGS OUT; ALL NEBRASKA LOCAL BROADCAST, TV OUT

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James Koolhof surveys the damage at his home on Lake Panorama, Iowa, Monday, May 12, 2014. At least eight condos in the Boulder Cover Condo Association were heavily damaged after a storm ripped through two sections of Lake Panorama, Sunday, May 11, 2014. The National Weather Service plans to send a survey team to the area to determine whether the damage was caused by a tornado. (AP Photo/The Des Moines Register, Zach Boyden-Holmes)

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Emilia Merritt, 18, looks at the damage to her car after a tree fell during a storm at her home on Panorama Dr. in Lake Panorama, Iowa, Monday, May 12, 2014. At least eight condos in the Boulder Cover Condo Association were heavily damaged after a storm ripped through two sections of Lake Panorama, Sunday, May 11, 2014. The National Weather Service plans to send a survey team to the area to determine whether the damage was caused by a tornado. (AP Photo/The Des Moines Register, Zach Boyden-Holmes)

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At least eight condos in the Boulder Cover Condo Association were heavily damaged after a storm ripped through two sections of Lake Panorama, Iowa, Sunday, May 11, 2014. The National Weather Service plans to send a survey team to the area to determine whether the damage was caused by a tornado. (AP Photo/The Des Moines Register, Andrea Melendez)

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At least eight condos in the Boulder Cover Condo Association were heavily damaged after a storm ripped through two sections of Lake Panorama, Iowa, Sunday, May 11, 2014. The National Weather Service plans to send a survey team to the area to determine whether the damage was caused by a tornado. (AP Photo/The Des Moines Register, Andrea Melendez)

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Refuge biologist Jessica Bolser assesses the condition of a bird's wings Saturday, May 10, 2014, during a bird-banding event at the Port Louisa National Wildlife Refuge near Wapello, Iowa. (AP Photo/The Muscatine Journal, Sarah Tisinger)

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Refuge biologist Jessica Bolser tags a bird Saturday, May 10, 2014, during a bird-banding event at the Port Louisa National Wildlife Refuge near Wapello, Iowa. (AP Photo/The Muscatine Journal, Sarah Tisinger)

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In this undated photo provided by the U.S. Army is Spc. Shawn N. Bounds. Army officials say the Alaska-based paratrooper from Texas has died in a traffic accident northeast of Anchorage, Alaska. Bounds, of Tyler, Texas died early Saturday, May 10, 2014, when his vehicle rolled in the public use area of the Knik River. Bounds deployed to Afghanistan from December 2011 to September 2012. (AP Photo/U.S. Army)