OMAHA, Neb. -- More than a dozen possible tornadoes were reported Saturday as forecasters warned residents across the nation's midsection to brace for "life-threatening" weather.
Reported tornadoes targeted Nebraska, Kansas and Oklahoma, and strong storms pushed through Iowa during the day. But the most dangerous weather was expected to come Saturday night into Sunday morning.
National Weather Service officials issued a stern warning for residents across a wide area to prepare for active overnight storms that could spawn fast-moving tornadoes.
On Saturday afternoon, an apparent tornado took down barns, outbuildings and large trees in southeast Nebraska. Johnson County emergency director Clint Strayhorn said he was still trying to determine how long the twister was on the ground and how much damage it did.
"I'm on a 2-mile stretch that this thing is on the ground and I haven't even gotten to the end of it yet," he said Saturday afternoon as he walked the path of destruction near the Johnson-Nemaha county line.
He didn't immediately know of any injuries.
In northeast Nebraska, Boone County Sheriff David Spiegel said baseball-sized hail had damaged vehicles, shattered windows and tore siding from houses in and around Petersburg, about 140 miles northwest of Omaha.
Two possible tornadoes were reported father south in Nebraska near the Kansas border, and as many as 10 others were reported in largely rural parts of western and central Kansas, including one north of Dodge City that was said to be on the ground for a half-hour, weather officials said.
In Salina, Kan., tornado sirens sounded after a possible tornado was spotted nearby. National Weather Service meteorologist Mike Scott also said tornadoes were reported in the central and western Kansas counties of Pratt, Stafford, Rush and Hodgeman.
There were reports of a home damaged in Rush County and an old schoolhouse in Hodgeman County. There also were reports of downed power lines and trees in Russell County.
Sharon Watson, spokeswoman for the Kansas Division of Emergency Management, said officials will continue to monitor the storm into early Sunday.
"We will be working closely to make sure we can help any counties that will need our assistance tonight," she said.
Michelann Ooten, an official with the Oklahoma Department of Emergency Management, said: "This could go into, certainly, to overnight situations, which is always of immense concern to us."
Storms that hit during the overnight hours can be more hazardous, as residents may not be able to hear tornado sirens in their sleep or don't monitor news services as closely. When it's dark, it's also more difficult for weather spotters to clearly see funnel clouds or tornadoes.
"The threat isn't over with tonight, unfortunately. Severe weather is possible again tomorrow from east Texas and Arkansas and up into the Great Lakes," said Bill Bunting, chief of operations at the Storm Prediction Center, which is part of the National Weather Service.
Tornado sirens sounded across Oklahoma City before dawn Saturday, and at least three possible tornadoes were reported west and north of the city in the central part of the state, Ooten said.
One of the suspected tornadoes in central Oklahoma hit near the small town of Piedmont, and followed a similar path as a tornado last May that killed several people, Mayor Valerie Thomerson said.
Later Saturday, several tornadoes were reported to have touched down in northwestern Oklahoma, causing minor damage. Officials confirmed two tornadoes in Woodward County, one of which damaged an outbuilding and a camper. No injuries were reported. A tornado also touched down in Woods County, where more than 5,000 people had gathered for a rattlesnake hunt at a state park.
The county's Emergency Management Director, Steve Foster, said most people were evacuated and others took shelter. In Iowa, strong storms knocked out power in Des Moines, Council Bluffs and Sioux City.
The National Weather Service in Des Moines also received reports of high winds that toppled at least five semis on Interstate 29.
The Storm Prediction Center gave the sobering warning that the outbreak could be a "high-end, life-threatening event."
It was just the second time in U.S. history that the center issued a high-risk warning more than 24 hours in advance.
The first was in April 2006, when nearly 100 tornadoes tore across the southeastern U.S., killing a dozen people and damaging more than 1,000 homes in Tennessee.
It's possible to issue earlier warnings because improvements in storm modeling and technology are letting forecasters predict storms earlier and with greater confidence, said Chris Vaccaro, a spokesman for the National Weather Service.
In the past, people often have had only minutes of warning when a siren went off.
"We're quite sure (Saturday) will be a very busy and dangerous day in terms of large tornadoes in parts of the central and southern plains," Vaccaro said Friday. "The ingredients are coming together."
The threat prompted University of Nebraska-Lincoln athletic officials to cancel the annual spring football game minutes before Saturday's kick-off.
The school expects to take a $400,000 hit in revenue from the sales of concessions and merchandise.
The McConnell Air Force Base in Wichita, Kan., relocated 16 aerial refueling tankers to Grand Forks Air Force Base in North Dakota because of the risk of hail from the storms.
And four air refueling aircraft from Forbes Field in Topeka were flown to Kirtland Air Force Base in New Mexico, and three other aircraft were moved into hangars to protect them from the potential for large hail in the Shawnee County area.
The Associated Press