Thunderstorms require three conditions: unstable warm air, moisture, and a lift mechanism. When warm moist air rises, it cools and condenses to form cumulonimbus clouds. Water droplets collide and fall as rain. Thunderstorms can cause flash flooding and hail damage, and lightning occurs when warm and cool air interact within storm clouds or between clouds and the ground, heating the air to over 30,000 degrees Celsius and creating thunder.