Flexi Says: Thunderstorms form when the ground is really hot. The air near the ground becomes very warm and humid. This is true in some locations in late afternoon or early evening in spring and summer. The warm air rises rapidly, which creates strong updrafts. When the rising air cools, its water vapor condenses. The updrafts create tall cumulonimbus clouds. Winds blow the cloud top sideways. This makes the well-known anvil shape of a cloud known as a thunderhead. Water droplets and ice fly up through the cloud. When these droplets get heavy enough, they fall. This starts a downdraft. A convection cell develops within the cloud. A mature thunderstorm produces gusty winds, lightning, heavy rain, and hail.