The answer may depend on where you live and what you are accustomed to. We did the Arizona/Utah trip on the first week of July in 2011. The day we arrived in Phoenix it was 107. But to me, it did not seem as hot as it was at home in Nashville, because of the lack of humidity. Once we left Phoenix it was much cooler. It was in the 80's at the Grand Canyon, which I believe is typical for that time of year. I'm sure it was in the 90's for most of the rest of the trip, but at no time did it seem hot to me, even when we were out hiking in the sun. Before the trip I was concerned about the heat and I doubted that the lack of humidity was going to make much difference, but it actually did. Funny thing was, all the locals kept telling us that monsoon season had come early and complaining about the humidity. It was around 20%, and that was unusally high for the area. I'm used to 90-100% in the summer, so that seemed like nothing to me.