I rolled over my ESU4 futures to ESZ4 today, and I noticed that the spread has been getting wider (although still less than 1 tick) as the day goes on. Just after 9:30 ET, the calendar spread was -7.95 x -7.90, and now it's -8.15 x -8.10. Is this typical? Only reason I can think of is that the front month futures are moving up toward the spot more quickly than are the far month futures. But a movement of .20 over a few hours on a single day seems kind of high, considering that, hypothetically, if SPX stays where it is the December futures only need to move $8.65 higher over the next 98 days.