Thunderstorms form when warm, moist air rises quickly into colder air above it.

The longer version

A thunderstorm needs moisture, unstable air, and something to lift it. Warm, humid air near the ground is less dense than the colder air above, so once it is nudged upward it keeps rising on its own, rather like a bubble in water.

As the rising air cools, its vapor condenses into cloud and releases heat, which makes the air even more buoyant and drives the updraught harder. A towering cloud builds, and inside it the churning of ice and water separates charge until electrical discharges occur. The storm fades once its updraught is cut off by the cool outflow of falling rain.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.