http://www.fly.faa.gov/adv/advAdvisoryForm.jsp
Your best resource for real time facts. The shorthand & coding aren't difficult to learn. Remember all times shown are Z, so you'll need to change the drop-down to Saturday.
ORD/MDW really took a beating this afternoon from the thunderstorms that are common this time of year. At least one of the G/S was per United's request, presumably because of ramp/gate gridlock due to too many arrivals on the ground when the weather moved in. If they can't get the departures out & off, things stop moving really quickly.
There's still a CUN-ORD diversion on the ground @ MCI from early this evening...prolly many similar flights all over the country.