It is a combination of very dry air, terrestrial effects as EFPotter discussed, and a diurnal effect that generally produces a high pressure during heating hours and a low pressure during cooling hours. They are commonly know as "thermal" His and Lows. Really one could look at the thermal pressure changes as a result of the temperature changing. But as it occurs, it in turn allows for accelerated heat loss.
Dry air heats and cools much faster than moist air. This is because once the air temperature reaches the dewpoint, condensation MUST begin for the temperature to fall any lower. The water in the air must begin releasing latent heat to do this.
So, if you are in an area like the desert that usually has a dewpoint well below the temperature (very dry air) the heat is free to go for a good while before condensation must begin.