Cloud Types common cloud classifications. Clouds are classified into a system that uses Latin words to describe the appearance of clouds as seen by an observer on the ground. The table below summarizes the four principal components of this classification system (Ahrens, 1994). Further classification identifies clouds by height of cloud base. For example, cloud names containing the prefix cirr-, as in cirrus clouds, are located at high levels while cloud names with the prefix alto-, as in altostratus, are found at middle levels. This module introduces several cloud groups.