Why are my Thursday runs so much slower than my Tuesday runs?

Is it because I'm so much more tired by the time the end of the week rolls around? Or just cause I'm a lame-o? My ten miles today went well, although the pace was a full 32 seconds per mile slower than it was on Tuesday. I try to run my Tuesday and Thursday runs at the same pace, and I run in the same area, I just can't seem to pick up the pace at all on Thursdays though. Oh well, at least I got it done.
I was exhausted when I got done though. I've decided that part of the reason I didn't do so well in Chicago this past fall was because I wasn't really prepared well enough. I can tell a huge difference between my last training plan and this one, and I'm only two weeks (not even two full weeks) into this plan. I think it's going to make a big difference running fewer days but more mileage, I hope.
I kind of think that maybe I got a smidge dehydrated on the run today too, as I've felt like ass pretty much all afternoon since I got back. I didn't carry my fuel belt and it was fairly close to sixty degrees today. I know, what's up with that? You've gotta love these warmer winters. I've got it on good authority though that the niceness won't last forever though, so I've got to enjoy it while I can.
On a different note, I tried to make my coconut creme pie for Christmas Eve today. It's cooking as I type. I'm less than convinced that it will turn out well, so I may be making an emergency trip to the grocery store tomorrow for a store bought one that I can pass off as my own. I know, that's cheating, but trust me, it's worth it.