Forecasters are warning 63 million people in the central U.S. to have an eye out for bad weather.

National Weather Service forecasters say colliding air masses threaten to generate high winds and possibly tornadoes. The threat Wednesday stretches from San Antonio to Chicago to Cincinnati. Missouri, southern Illinois and northern Arkansas face the greatest severe weather threat.

The current forecast calls for south winds of 10 to 20 miles per hour with gusts to 30 on Wednesday. Winds Wednesday night are expected to shift to the west and increase to 20 to 30 miles per hour with gusts to 40 miles per hour. Windy conditions are expected through Thursday.