Average high around 90, average overnight low in the upper 60's. Humid, nasty bugs that leave itchy welts that last for weeks. On the bright side it's not crowded.
What we did was start off early on the east side of the canyon and climb until the sun comes over the top. Then go find a shady spot to eat lunch and hang out a few hours. Then go over to the West/Southwest side since they're shaded in the afternoon. If you're looking for an area that's several degrees cooler, go to the corridor on the far west side of the north forty; it's a great spot to have lunch when it's really hot out.