High clouds form in the highest and coldest region of the troposphere from about 5 to 12 km (16,500 to 40,000 ft) in temperate latitudes. At this altitude water almost always freezes so high clouds are generally composed of ice crystals or supercooled water droplets. Genus cirrus Abbreviation: Ci Cirriform clouds tend to be wispy and are mostly transparent or translucent. Isolated cirrus do not bring rain; however, large amounts of cirrus can indicate an approaching storm system eventually followed by fair weather. There are several variations of clouds of the cirrus genus based on species and varieties: Species Cirrus fibratus (V-1) High clouds having the traditional "mare's tail" appearance. These clouds are long, fibrous, and curved, with no tufts or curls at the ends. Cirrus uncinus (V-2) Filaments with up-turned hooks or curls. Cirrus spissatus (V-3) Dense and opaque or mostly opaque patches. Cirrus castellanus (V-4) A series of dense lumps, or "towers", connected by a thinner base. Cirrus floccus (V-5) Elements which take on a rounded appearance on the top, with the lower part appearing ragged. Varieties Opacity-based None; always translucent except species spissatus which is inherently opaque. Fibratus pattern-based Cirrus fibratus intortus (V-6) Irregularly curved or tangled filaments. Cirrus fibratus vertebratus (V-7) Elements arranged in the manner of a vertebrate or fish skeleton. Pattern-based variety radiatus Large horizontal bands that appear to converge at the horizon; normally associated with fibratus and uncinus species. Cirrus fibratus radiatus (V-8) Cirrus uncinus radiatus (V-9) Pattern-based variety duplicatus Sheets at different layers of the upper troposphere, which may be connected at one or more points; normally associated with fibratus and uncinus species. Cirrus fibratus duplicatus (V-10) Cirrus uncinus duplicatus (V-11) Spissatus, castellanus, or floccus Varieties are not commonly associated. Supplementary features Precipitation-based Not associated with cirrus. Cloud-based Mamma Bubble-like downward protuberances; mostly seen with species castellanus. Genitus mother clouds Cirrus cirrocumulogenitus Cirrus altocumulogenitus Cirrus cumulonimbogenitus Cirrus homogenitus Cirrus formed by spreading of aircraft contrails. Mutatus mother cloud Cirrus cirrostratomutatus Cirrus homomutatus Cirrus formed by the complete transformation of cirrus homogenitus. Genus cirrocumulus Abbreviation: Cc. High-level stratocumuliform clouds of the genus cirrocumulus form when moist air at high tropospheric altitude reaches saturation, creating ice crystals or supercooled water droplets. Limited convective instability at the cloud level gives the cloud a rolled or rippled appearance. Despite the lack of a strato- prefix, layered cirrocumulus is physically a high stratocumuliform genus. High stratocumuliform species