Heavy rainfalls are often associated with cumulonimbus clouds.
Cumulonimbus clouds are large and vertically developed clouds that are capable of producing thunderstorms, heavy rain, hail, and even tornadoes. They form in unstable atmospheric conditions where warm, moist air rises rapidly, cools, and condenses into clouds.
The top of the cumulonimbus cloud often has a distinctive anvil shape, which is created by the strong winds at high altitudes that blow the top of the cloud into a flat shape.
Heavy rainfall occurs when the warm, moist air within the cumulonimbus cloud rises and cools, causing the water droplets within the cloud to condense into raindrops. As the raindrops become too heavy for the updrafts within the cloud to support, they fall to the ground as heavy rain.
Cumulonimbus clouds are often associated with thunderstorms, lightning, and strong winds, making them a potentially dangerous weather phenomenon.