Cumulonimbus- A thunderstorm cloud (pictured at right). Cumulonimbus can tower over 60,000 feet (over 11 miles) up into the sky. Smaller cumulonimbus (30,000 feet) can still produce lightning, high winds, heavy rain, and sometimes tornadoes. When a cumulonimbus cloud reaches the top of the troposphere, its top will flatten and spread out into an 'anvil' shape. Cumulonimbus clouds are the product of strong convective activity. A rapidly growing cumulonimbus cloud's upper edges will usually look hard and rounded, like cauliflower, as it protrudes skyward: