Which clouds are the highest in the sky?
High clouds (Family A) These generally form above 16,500 feet (5,000 m), in the cold region of the troposphere. However, in Polar regions, they may form as low as 10,000 ft (3,048 m). They are denoted by the prefix cirro- or cirrus. At this altitude, water almost always freezes so clouds are composed of ice crystals. The clouds tend to be wispy, and are often transparent. Clouds in Family A include: Cirrus (Ci) Cirrus uncinus Cirrus Kelvin-Helmholtz Colombia Cirrostratus (Cs) Cirrocumulus (Cc) Pileus Contrail, a long thin cloud which develops as the result of the passage of an aircraft at high altitudes.
