We lucked out when we did it. It absolutely poured prior to the parade, so cooled things off a bit. Stopped raining right before the parade started, so we went to our viewing area. Sun did not come back out to heat things up until after the parade ended. Great time! And, this is before the dragon fired herself.
But, I'm not sure I would book this again in the middle of the summer. It can be HOT in that area in the middle of the day!