Forecasters: Dangerous storms moving into Midwest

Tornado sirens sounded across Oklahoma City before dawn, and at least three possible tornadoes were reported west and north of the city, said Oklahoma Department of Emergency Management official Michelann Ooten. Some homes were damaged, though no injuries were immediately reported in any of the states.

But the most dangerous weather was expected later in the day, 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 to into the Great Lakes," said Bill Bunting, chief of operations at the Storm Prediction Center, which is part of the National Weather Service.

The same weather system will move into the Carolinas early next week, but it will have lost much of its intensity by that time, said WRAL meteorologist Aimee Wilmoth. 

"The Triangle is looking at a very calm day with clear skies again on Sunday," she said. "High pressure off the coast is in control of our weather."

It won't be until Tuesday that the Triangle sees any effects of the front that was spawning storms in the Midwest Saturday, and by then it will just bring the chance for showers and thunderstorms, Wilmoth said.

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.

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.