A cumulonimbus cloud is a type of towering cloud associated with thunderstorms and severe weather. These clouds are characterized by their towering height, often reaching up to the stratosphere, and are known for producing heavy rainfall, lightning, and even tornadoes. They typically have a flat, anvil-shaped top and can develop rapidly under unstable atmospheric conditions. Cumulonimbus clouds are vital to the water cycle but also pose risks due to their association with severe weather events.