What is a cumulonimbus cloud?

Cumulonimbus clouds are the giants of the sky, formed by powerful rising columns of warm, moist air called updrafts. As the air rises and cools, water vapour condenses and releases heat, fuelling the cloud to build higher and higher, sometimes reaching the top of the troposphere around 12 km up or more. At that height the cloud often flattens into a distinctive anvil shape as it hits stable air. These clouds contain enormous energy and are responsible for thunderstorms, torrential rain, lightning, hail, strong winds, and in severe cases tornadoes. Pilots avoid flying through them because of the intense turbulence and hazards they hold.