Thunderstorms are caused by a collision of warm air and cold air. A thunderstorm is a cloud formation where large amounts of water undergoes a cycle of condensation, freezing then revaporizating as the currents of vapor within the cloud rises and falls. This produces static electricity which discharges as lightning. Thunderstorms are caused by a collision of warm air and cold air. A thunderstorm is a cloud formation where large amounts of water undergoes a cycle of condensation, freezing then revaporizating as the currents of vapor within the cloud rises and falls.