A storm that has thunder and lightning is called a thunderstorm. The sky gets dark as it fills with cumulonimbus clouds. The wind blows in gusts. Raindrops start to fall. And then - boom! - there’s lightning and a rumble of thunder. 

For a thunderstorm to form, moisture needs to be in the air for clouds and rain, and air needs to be flowing upward in the atmosphere. Often air moves up when it’s warmed near the ground. At the same time, cold air sinks from high in the atmosphere. Air moving up and down is called convection. And that moving air is also what causes thunder and lightning

A large thunderstorm over flat grasslands. Rain is falling from the bottom of a towering cumulonimbus cloud.

Cumulonimbus clouds like this one start out as cumulus clouds and grow taller until they make a thunderstorm. Do you see the rain falling from the lowest part of this cloud? The area that looks dark gray where the land meets the sky is where rain is falling. 

Brian Khoury/CC BY-ND 2.0