O'Hare International Airport was reporting delays of up to three hours for inbound and outbound flights. More than 550 flights have been canceled by the airlines there.
Midway reports delays of more than 45 minutes for many flights and minor cancellations as of 11 a.m.
A line of thunderstorms will lift Wednesday morning before redeveloping in the afternoon and moving from southwest to northeast across the Chicago area. Severe thunderstorms are most likely to occur south of I-80 in northeastern Illinois and northwest Indiana.
The Sun-Times Media Wire contributed to this report.