Desert climate is one of the extremes. It is known that aridity is the defining characteristic of a desert and some places can be extremely arid, receiving precipitation as an exception rather than as a rule. The highest maximum temperatures too are recorded in deserts, as the sun shines strongly in the cloudless skies during the day. However, the lack of moisture also allows terrestrial radiation to escape quickly so that it can get quite cold soon after the sun sets. Hot deserts are generally warm throughout the year. Mean annual temperatures are above 20˚C. They are extremely hot in summer, with daytime temperatures well in excess of 40˚C. Places such as Jacobabad (Pakistan), Death Valley (California, USA), and Azizia (Libya) have recorded temperatures higher than 50˚C. The clear skies and low humidity also allow for high diurnal and annual ranges of temperature. This is more so in sandy deserts than rocky deserts. Hot, dry winds, such as the khamsin in Egypt and the sirocco in northern Africa, blow sand across the desert, making conditions even more difficult. 

Precipitation is not only low, but it is also erratic. Average precipitation figures have little meaning as several years of no rainfall may be suddenly followed by heavy rain in one year. Rain, when it comes, is in the form of short, violent showers, which may result in flash floods. Lighter showers are ineffective, as 69 the moisture they bring evaporates in no time. The Atacama Desert in northern Chile in South America is the driest place in the world. Some weather stations in this desert have never recorded any rain. Mists are common in the coastal parts of deserts like the Atacama and the Kalahari. The fog that forms over the ocean is blown inland by the wind. Moisture from fog drip is sufficient to support a vegetation cover on the coastal hills.