Phoenix and Las Vegas are farther north than Atlanta and Miami but are much warmer. Why should this be?
—Thad Morrison, Lombard
Terrain, atmospheric moisture, and cloud cover explain it. The typically haze and cloud-free desert environment — outside the monsoon season — permit strong sunlight to heat desert sand and rock more efficiently. Once warmed, these surfaces radiate heat to the atmosphere and keep temperatures high, even at night. When close to mountains from which air descends, such as Phoenix and Las Vegas, compressional warming takes place. By comparison, Atlanta and Miami are more humid and have hazier skies, more cloudiness, and more frequent precipitation. Such an atmosphere does not heat as efficiently as in a more arid climate.