Dry climates produce less than ten inches of rain a year. Some areas may receive more but lose it all due to evaporation. These desert climates can be hot, cold, or mild and are generally low in humidity.
The hot deserts have perpetually sunny, clear skies year-round and extremely high temperatures, though these can drop to freezing at night due to the same clear skies that permit heat dissipation. They are almost always in the tropics. Assign this climate to tropical deserts.
The cold deserts have similar hot summers, but the winter can be far below freezing. They occur at higher altitudes, are drier, and are in temperate zones (north of the tropics in the northern hemisphere, south of them in the southern). They are also usually in the rain shadow of a mountain range.
The mild desert climates are mild throughout the year and are usually found along the western edges of continents or at high altitudes (plateaus or steppe deserts). They are caused by cold ocean currents offshore. Deserts by the coast often have fog and low clouds.