Another factor is humidity, note current dew points:

Pinehurst, NC 69 °F
Paris, France 57 °F
Alpe D'Huez, France 52 °F
Salt Lake City, UT 45 °F

Living in the mid-Atlantic myself I know that 69 is about as good as it gets in the summer, 75 is typical. So this year in the TDF when riders were complaining about the heat, it was a little warm, but for someone from this area, 90 degrees with a 57 degree dew point would feel more like late October.