A thunderstorm is a disturbance in the atmosphere that is characterized by lightning and thunder. Lightning is an electrical discharge in the air generated by charged particles in moving air masses. Because lightning is a phenomenon of moving, charged particles, not rain, we see lightning in violent forest fires and volcanoes as well as thunderstorms. Thunder is the sound produced by the shock wave lightning generates. The air immediately around lightning is suddenly heated to high temperatures—up to 30,000°C (54,000°F)—and subjected to high pressure; it expands rapidly.