Marathon runners took shelter early Sunday as hail and high winds delayed a race dedicated to victims of the 1995 Oklahoma City bombing, and forecasters warned people in the nation's mid-section to prepare for tornadoes and hurricane-force winds.

Race organizers delayed the Oklahoma City Memorial Marathon by 105 minutes to let a severe thunderstorm pass through. With skies still gloomy, marathon organizers tweeted a photo from downtown with the caption: "Lined up and ready to run!"

And after 168 seconds of silence to remember bombing victims, the race started at 8:15 a.m.

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

"The greatest risk for a few intense tornadoes will exist across much of Arkansas perhaps into western and central Missouri," an advisory from forecasters said. Storms could also reach the Delta region of northwestern Mississippi late in the day.

Hail and high winds could hit the areas that don't see tornadoes, the forecasters said. They warned that hail could be the size of baseballs and wind gusts could reach hurricane-force: 75 mph or higher.

Sunday's marathon had been set to start at 6:30 a.m., but strong storms formed overnight in western Oklahoma and approached the state capital just before sunrise.

Race organizers already had arranged for three shelters to be used along the 26.2-mile route — just in case — but when the storm came early downtown businesses opened their doors to give runners in their shorts, commemorative T-shirts and bibs and place to wait.

Oklahoma City's marathon is held each year near the anniversary of the bombing. On April 19, 1995, Timothy McVeigh loaded a truck with fuel oil and fertilizer and exploded it outside the city's federal building, killing 168 people. A museum, memorial garden and reflecting pool now fill the site of the blast.