How do clouds form?
Clouds form when warm, moist air rises and cools. The water vapor condenses onto tiny particles of dust, salt or smoke, creating billions of small water droplets or ice crystals.
Air always contains some invisible water vapor. When air rises, it expands and cools because pressure is lower higher up. Cooler air cannot hold as much water vapor, so once it reaches a temperature called the dew point, the vapor condenses into liquid droplets. Each droplet forms around a tiny particle called a condensation nucleus.
Air can be lifted in several ways: by warm ground heating the air above it, by wind pushing air up mountains, or by warm air sliding over cold air along weather fronts. The way air rises affects the type of cloud, from flat sheets to tall, towering shapes.
Types of clouds
Clouds are named using Latin words. Cumulus clouds are puffy heaps, stratus clouds form flat layers and cirrus clouds are thin, wispy streaks made of ice high in the sky. Cumulonimbus clouds can grow more than 10 kilometers tall and bring thunderstorms, heavy rain and hail.
Did You Know?
An average cumulus cloud can weigh about 500 tonnes, roughly as much as 100 elephants, but the water is spread out over a huge volume of air.