Forecasters warned residents in many Midwestern and southern states to be alert Sunday as the threat of severe weather and tornadoes intensified.

The risk of tornadoes will rise throughout the day, centered in an area stretching from Omaha, Neb., to northern Louisiana, the National Weather Service’s Storm Prediction Center in Norman, Okla., said. Some twisters could be particularly strong in the late afternoon and evening.

“The greatest risk for a few intense tornadoes will exist across much of Arkansas perhaps into western and central Missouri,” a weather service advisory said, noting the Delta region of northwestern Mississippi also could be affected late in the day.

A strong storm moved through west central Missouri on Sunday afternoon. The Missouri Highway Patrol reported a tractor-trailer was blown onto its side on Interstate 70 about 30 miles east of Kansas City about 1 p.m. No injuries were reported.

Tornado watches — which means twisters could develop but aren’t an immediate threat — were widespread in the Plains states Sunday, targeting an area from north central and eastern Kansas, western and central Missouri and central Nebraska and southern Iowa.

Even if tornadoes don’t form, some areas could see hail and high winds, forecasters said, warning the hail could be as big as baseballs and wind gusts could reach hurricane-force — 75 mph or higher.

Severe thunderstorms will move into Arkansas, southern Missouri, eastern Oklahoma and extreme northeast Texas on Sunday afternoon into Sunday evening. The greatest risk of tornadoes developing will be centered in Arkansas.

To the southeast, northern Louisiana and Mississippi were bracing for severe storms along with the possibility of flash flooding. The predictions prompted Barksdale Air Force Base near Bossier City, La., to cancel its air show on Sunday. The National Weather Service said northern Alabama could see rain and flash flooding, while central and northern Georgia could see storms and heavy rain.

Meanwhile, runners in Oklahoma City took shelter early Sunday as hail and high winds delayed the Oklahoma City Memorial Marathon by 105 minutes to let a severe thunderstorm pass through.

Race organizers already had arranged for three shelters to be used along the 26.2-mile route, but when the storm came early, downtown businesses opened their doors for the runners. The race is dedicated to the victims of the 1995 bombing, which killed 168 people.

(AP)