The truth is, there is no way to predict the weather. That being said, being from Chicago I suspect you will find it to be much warmer than expected! We are from Milwaukee and were there the week after Thanksgiving last year. Everyone told us to bring layers. Well, we didn't use our sweatshirts or jackets once! We were in shorts and t-shirts the whole time, even at night. It stays pretty warm in the parks with all that concrete.
How funny! This just shows how variable the weather is during Nov. We were there at thanksgiving last year and not only used our sweatshirts in the am but one day never took them off it never got above 62 that day! DS wore a light fleece hat to rope drop (of course that was way before the sun was up since we were out the door by 6 am for EMH!