I didn't get time to post before my flight. I looked at all the charts (except jet stream) an hour departure, didn't see too much that looked menacing. Take off and first 20 minutes were perfect, pilot announced that we would be flying at 40,000 ft and he expected a smooth flight. As soon as we got to N.Florida the bumps started as chops, then moved to moderate. We descended to 36,000 looking for smooth air, but not much luck on that. Then he changed the flight plan, instead of heading north over Indianapolis, we flew west over St. Louis! Light-mod all the way into ORD, seat belt sign on the whole flight, followed by a descent and landing in fog so thick we were almost over the field before we saw the ground, so I'm not sure what benefit there was by avoiding the area S.E. of ORD. Can you tell me? Thanks!