As you may have heard, a fire at Chicago's traffic control facillty is strongly affecting the area to the point of almost complete shut down.
ORD and MDW only accept limited arrivals and the FAA says the facility could be closed for days—which might prove a big headache.
O'Hare handled 883,000 takeoffs and landings in 2013, which makes it the second busiest airport in the world. The disruption is affecting the entire US and lots of international flights.
If you want to get updated, you can check this little nifty website that was just created: ischicagoflying.com
Current status? O'Hare: Very limited arrivals overall. Midway: Very limited. Scheduled arrivals diverted.