- A thunderstorm starts with an updraft, which lifts warm, moist air. As the air rises, it cools, causing the water to condense. As the water condenses, it releases heat into the air, causing the moist air to become less dense and continue to rise. This forms a large, unstable cloud called a cumulus.
- The water at the top of the cloud begins to freeze. It is unable to climb any higher, and starts to flatten and spread, becoming a cumulonimbus cloud. The ice crystals at the top begin to fall, creating a downdraft within the cloud. As they fall, they melt, absorbing heat and creating an even stronger downdraft. In most thunderstorms, there is still an updraft as this happens, which creates turbulence, wind and lightning.
- As the downdraft increases, it eventually overwhelms the updraft. No more water molecules are freezing, which means there is no more heat being released to feed the updraft. Usually, the storm exhausts itself at this point, as the rain lessens and the wind calms. Some storms end with a burst of wind as the downdraft gathers power.
