Clouds hardly ever form in deserts because the air is so warm that it can hold lots of water vapour without it condensing. This makes rain very rare.
The Atacama desert in northern Chile is the driest desert on Earth. Parts of the desert had no rain for 400 years, from 1570-1971, and in other parts, rain has never been recorded.
With no clouds to block the Sun's rays, the ground becomes baking hot. Surface temperature of at least 40oC are not uncommon. At 57oC, Death Valley is the driest, hottest place in North America. Gold prospectors died there, in 1849, when they ran out of food and water on their way to the Californian goldfields - which is how the valley got its name.
Nights can be very cold, though, and even frosty in winter, because cloudless skies let heat escape.
Strong trade winds blow across the deserts. In sandy deserts, the wind sweeps up fine sand and causes dust storms up to 3,000m high. As sand is blown along, it erodes rocks in its path. Over many years, the rocks may be sand-blasted into weird, sculptural shapes.
The total rain for the year usually falls in just two or three heavy storms. The water does not soak in straight away, but runs rapidly across the surface, sweeping up valley debris and carrying it along wide channels called wadis. Deep canyons may be formed too.