For forecasting purpopses, clouds are divided into 2 groups: cumulus clouds and stratus clouds. Clouds are also classified according to their height above the ground and are destinguished as high, middle, and low altitude clouds.
Cloud Composite Illustration
Groups
Cumulus Clouds
Heaped clouds resulting from rising unstable air currents. Appear as flat-based with a cauliflower-like dome created by ordinary convection. If the upward current continues, the dome will develope turrents, and the cloud is then called a cumulus congestus, or towering cumulus. It may produce light showers. If the convection process continues, a large cumulonimbus may result, with the possibility of a thunderstorm.
Stratus Clouds
Layered resulting from stable air. Appear as wide sheets, or layered, with minimal vertical and extended horizontal domensions. Sometime covering the entire sky. There is little or no convection present. They are created when layers of air with different temperatures come into close contact with each other. Cumulus and stratus clouds sometimes coexisit.
Classifications
These altitudes apply to the temperature zone the clouds are in, and whether or not they produce precipitation.
High Clouds
These generally form above 18,000 feet (5,486m), 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. These clouds are white and thin, can be seperated or deatached, form delicate veil-like patched or extended wispy fibers, and often have a feathery appearance. They usually have the prefix "cirro-," which is acombination form of the word cirrus, which means a lock of hair.
Middle Clouds
Between altitudes of 6,000 and 18,000 feet (1,829-5,486 m) are clouds that form the main portion of active weather systems moving across the continent. Middle level clouds may resemble higher-altitude clouds in general apperance but are made mostly of liquid water droplets. Middle-altitude clouds are generally of the stratus type, indicating that the air is stable and without vertical currents. They usually have the prefix "alto-," meaning middle.
Low Clouds
Low-altitude clouds are found below 6,000 feet (1,829 m). They are either flat, layered stratus sometimes dense and grey, or cumulus with flat bases and rounded tops. These cumulus clouds can transform into middle- or high-altitude when lifted by convection.
Cloud Variations
Some definitions of cloud species, varieties, supplementary features, and accessory clouds.