A. 6 miles (10 kilometers)

B. 12 miles (20 kilometers)

C. 19 miles (30 kilometers)

D. 25 miles (40 kilometers)

Extreme thunderstorms form in areas where the air is unstable—that is, where rising volumes of air remain warmer and less dense than the surrounding air and so continue to rise. (Where air is stable, a volume of air that is warmer than the surrounding air will rise until it either achieves equilibrium with the surrounding air and stops, or becomes colder and denser than the surrounding air and sinks back down.) This instability helps create strong currents of rising air (updrafts) that can penetrate the lowest part of Earth’s atmosphere (the troposphere) and the next layer up (the lower stratosphere). Strong updrafts can cause thunderstorms with large hailstones, tornadoes, heavy rainfall and lightning. Thunderstorm cloud tops have been seen more than 12 miles (20 kilometers) high by NASA’s Tropical Rainfall Measuring Mission (TRMM) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellites.