AKSAR and Montanero bring up a really key point to understanding this area - altitude is critical to anticipating the temperatures you will experience. At 7000 feet and above, you will be back in Minnesota. Below 4000, it will be like the inside of your furnace back hone - at least during midday. Since humidity is generally low, there are amazing swings in the daily temperature curve. If you are really talented and unfortunate, you can expose yourself to both hyper and hypo thermia in the same 24 hour period.

This will be less of an issue as you proceed north, but at the Grand Canyon, you will see an extreme example. I remember one trip, a rim to rim run, where we dodged snow drifts on the North Rim and ran into 100 + at Phantom Ranch, along the Colorado River, just three hours later.