A large-scale system characterized by deep convective clouds (cumulus congestus and cumulonimbus), various associated stratiform clouds, heavy precipitation, and a vigorous circulation. The last becomes progressively more organized as the system develops. In particular, the individual downdraughts tend to combine to produce a vigorous outflow, and a deep layer of cold air in the lower troposphere. At upper levels, the individual cirrus plumes combine to produce a large anvil or cirrus shield. The overall lifetime of such a system exceeds four hours, much longer than that of a normal, individual cumulonimbus cell.
Subjects: Meteorology and Climatology.