ORD is simply overwhelmed with flights in the afternoon. Didn't the FAA make (request that) all airlines trim their schedules during peak hours? Even without weather, ORD can barely function.

With that said, a couple years ago I made a connection DEN-ORD-FRA on a January day where ORD got over a foot of snow. The airport was a ghost town. Very eerie. I managed to make it on the only flight that actually made it DEN-ORD that morning. All of the international flights left pretty much on time since there was no arrival traffic to clog up the runways.