Cirrus clouds are formed when water vapor undergoes deposition at high altitudes where the atmospheric pressure ranges from 600 mbar at 4,000 m (13,000 ft) above sea level to 200 mbar at 12,000 m (39,000 ft) above sea level. These conditions commonly occur at the leading edge of a warm front. Because humidity is low at such high altitudes, this genus - type tends to be very thin. Cirrus clouds are composed of ice crystals that originate from the freezing of super cooled water droplets in regions where air temperature is lower than - 20 ° C or - 30 ° C. Cirrus usually occur in fair weather. They are formed when it is high enough to be cold and freeze the water drops into ice. They sometimes may be caused by turbulence and wind shear, or by upper - tropospheric convection. Sometimes they are like blown out ice - crystals spreading from the top of a dying cumulonimbus.
high level clouds that are mainly composed of ice crystals
Cirrus clouds Cirrus clouds