Cirrus Cloud

Base is typically between 20,000 and 40,000ft in the UK, and may be considerably higher in the tropics. Cirrus clouds do not produce precipitation which reaches the ground, though streaks of particles (known as fall streaks) are often observed below these clouds. Various halos and other optical effects may be produced by cirrus cloud. In some cases these clouds are also thick enough to hide the sun. Cirrus clouds typically form at temperatures below -40C and consist entirely of ice particles.