If the soil is parched, whatever solar energy is not reflected skyward is absorbed, thereby raising the temperature of the ground. The air in contact with the ground heats up as well. On the other hand, if the soil is moist from recent rains, much of the incoming solar energy is used to evaporate water near the surface. There is significantly less energy available to heat the soil. This has the effect of reducing the amplitude of the daily temperature wave.
Clouds affect the diurnal temperature range as well.
Clouds more than a few hundred meters thick reflect sunlight efficiently, about as well as new fallen snow, thereby reducing the solar energy reaching the ground. This lowers the maximum temperature that would be attained if the sky were clear. Warmer ground radiates significantly more energy than colder ground. Clouds absorb infrared radiation very effectively and re-radiate it back toward the ground at a rate dependent upon the cloud temperature. The temperature of low clouds is likely to be close to the temperature of the ground.