What causes thunderstorms to form?

Thunderstorms form when warm, moist air rises rapidly into the atmosphere and meets cooler air above. As the warm air rises, it cools and condenses, forming cumulonimbus clouds, which can grow large enough to produce lightning, thunder, and heavy rainfall. The energy from the condensation causes the air to expand rapidly, creating the booming sound of thunder. Thunderstorms are most common in warm, humid climates and can form during hot summer days when the atmosphere is unstable.