OMAHA, Nebraska - Tornadoes dropped onto the Great Plains on Thursday after forecasters had warned of a potentially historic outbreak, doing little harm early on but spooking a pair of circus elephants in Kansas that escaped their enclosure.

The animals rampaged through WaKeeney in northwestern Kansas, apparently frightened by the storm and sirens, said a Trego County sheriff's dispatcher named Dawn who would not give her last name, citing department policy. There were no immediate reports of damage as handlers tried to corral them, the dispatcher said.

A funnel cloud was spotted over southwestern Nebraska, and flood warnings and watches were issued for much of the state as streams and rivers overflowed, thanks to recent rainfall of more than 5 inches in places.

Large hail, strong winds and at least four tornadoes whipped through Kansas, with some roof damage reported at a small airport west of Wichita.

In a strongly worded statement Thursday, the weather service warned that parts of Kansas could see hail bigger than baseballs and "a few strong to violent long-lived tornadoes."

Wichita State University canceled evening classes because of the weather predictions.

Computer forecasting models for Thursday resembled those on June 8, 1974, when 39 tornadoes raked the southern Plains and killed 22 people. The National Weather Service on Tuesday took the unusual step of giving advance warning of a possible tornado outbreak based on the conditions.

Forecasters had said severe thunderstorms would form in Kansas and move toward eastern Kansas, Nebraska, northwestern Missouri and Iowa. Heavy rainfall and flooding were also possible, especially late Thursday night in southeast Kansas.

"The highest risk is central Kansas and the entire central portion of the country," said Brad Mickelson, a weather service meteorologist. "There is a high risk of severe thunderstorms."

Singled out as at high risk were Omaha; Topeka, Kan.; Des Moines, Iowa; and south-central Minnesota, he said. The region at risk of severe thunderstorms stretched from northern Texas to Minnesota and Wisconsin.

On Wednesday, storms soaked the Midwest and then moved across to the mid-Atlantic region. Three deaths were blamed on the storms.

Tornadoes touched down in southern Iowa, causing isolated damage in rural areas. Many rivers flooded.

"The rivers haven't had a chance to go down, and with the heavy rains, they just keep going higher," said Brad Fillbach, another meteorologist with the National Weather Service.

Fillbach said Creston, Iowa, which had a brush with a tornado Wednesday evening, had about 6 inches of rain by Thursday morning. Some roads were under 3 feet of water early Thursday.

"The weather has been real active this week. It'll be nice to get a few days to dry out and get these rivers back down," Fillbach said.

In the Washington metro area, Wednesday's storm downed tree lines and power lines, leaving more than 200,000 homes and businesses without electricity Thursday. Some outages could last for several days because of the severity of the damage, Pepco spokesman Bob Dobkin said.

Associated Press writers Roxana Hegeman in Wichita and Bill Draper in Kansas City, Mo., contributed to this report.