OMAHA, Neb. (AP) -- More than a dozen possible tornadoes were reported Saturday as forecasters warned residents across the nation's midsection to brace for "life-threatening" weather.
An apparent tornado took down barns, outbuildings and large trees in southeast Nebraska, and 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 as he walked the path of destruction near the Johnson-Nemaha county line. He described a line of downed trees and a barn that was destroyed. He didn't immediately know of any injuries.
"I'm trying to make sure everyone's OK," Strayhorn said.
In northeast Nebraska, Boone County Sheriff David Spiegel said baseball-sized hail 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. An old schoolhouse and outbuildings were damaged in Hodgeman County in western Kansas and a home was damaged near Lorretta in Rush County in central Kansas.
In Salina, tornado sirens sounded after a possible tornado was spotted near the central Kansas community. National Weather Service meteorologist Mike Scott said tornadoes also were reported near Sawyer in Pratt County, near Seward in Stafford County, near Timken and Rush Center in Rush County and near Hanston in Hodgeman County.
Sharon Watson, spokeswoman for the Kansas Division of Emergency Management, said officials will continue to monitor the storm into early Sunday.
"The challenge on this particular storm is the severity level that is being forecast across so much of the state. It is one that is causing us much concern and requiring a lot of attention to determine exactly what is happening," she said.
The most dangerous weather was expected to come later, and National Weather Service officials issued a stern warning for residents to prepare for overnight storms that could spawn fast-moving tornadoes. Officials said a large area could be at risk for dangerous storms.
"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.
"This could go into, certainly, to overnight situations, which is always of immense concern to us," said Oklahoma Department of Emergency Management official Michelann Ooten.
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, taking a similar path as a tornado last May that killed several people, Mayor Valerie Thomerson said.
"Because of last year, we've had a lot of new people put storm centers into place," the mayor said, adding that no major damage had been reported in the town northwest of Oklahoma City. "We're all very anxious about this afternoon."
Two tornadoes were reported to have touched down in northwestern Oklahoma, causing minor damage. An outbuilding and a camper were damaged in Woodward County, but no injuries were reported.
The Oklahoma Highway Patrol was working to get thousands of people attending a rattlesnake hunt at a state park near Waynoka to seek shelter.
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. While the $10 tickets are non-refundable, 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., has been relocating 16 aerial refueling tankers because of the risk of hail from the storms. Base spokeswoman, Lt. Jessica Brown, described the relocation of the planes to Grand Forks Air Force Base in North Dakota as a precaution, noting the tankers would be costly to fix.
The city of Norman, Okla., home to the University of Oklahoma campus, got a preview of the potential destruction on Friday when a twister whizzed by the nation's tornado forecasting headquarters but caused little damage. Norman Regional Hospital and an affiliate treated 19 people for mainly "bumps and bruises," hospital spokeswoman Kelly Wells said.
Associated Press reporters Sean Murphy in Oklahoma City; Heather Hollingsworth in Kansas City, Mo.; Erin Gartner in Chicago; and Ed Donahue in Washington contributed to this report.