Cumulonimbus clouds are large, towering clouds often associated with thunderstorms. They can reach great heights, sometimes extending up to 12 miles into the atmosphere. These clouds are characterized by their dense, vertical development and can produce heavy rain, lightning, and even hail. These clouds form when warm, moist air rises rapidly, cooling as it ascends. The top of a mature cumulonimbus cloud can spread out into an anvil shape, indicating strong updrafts. They are a key feature in severe weather patterns and are closely monitored by meteorologists for potential storm development.