Did anything get out on Sunday? It was the fifth largest snowfall in Chicago history. I suspect there were at least some major delays, if not complete cancelations.

More directly on point to the OP's question, a little snow doesn't even slow things down at ORD. Extreme cold can shut it down (like last year's fuel freezing episodes), and feet of snow can be an issue, but an inch or two is SOP at ORD. The Summer is far worse when the thunder storms come through.