What causes lightning to form in a thunderstorm?

Lightning forms in thunderstorms due to the separation of electrical charges within a cloud. Updrafts carry small ice particles upward, while heavier particles fall, creating collisions that generate static electricity. The top of the cloud becomes positively charged, and the bottom becomes negatively charged. When the charge difference becomes large enough, a discharge occurs, creating a lightning bolt. Lightning can occur within clouds, between clouds, or between a cloud and the ground.