The weekend forecast is an especially tricky call because Chicago will find itself in a chaotic region of rapidly changing weather conditions from Friday into Sunday. The area will transition from rain and near-record warmth to much colder temperatures, but the manner in which that shift occurs is critical. If temperatures fall low enough before rain departs, Chicago could receive a sloppy mix of rain then sticking snow late Saturday/early Sunday --- or not. Either way, the expected 46-degree temperature drop from Friday’s mild, near-record high of 60 degrees to Sunday’s low of 14 degrees will seem brutal, even though that huge drop merely returns city temperatures to normal mid-January levels. Chicago’s Saturday morning expected low, 49 degrees, is well above predicted lows in normally mild cities, like Phoenix (32), Las Vegas (26), Los Angeles (35) and San Diego (39).