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What is a cloud?
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Quick answer
A cloud is a visible mass of tiny water droplets or ice crystals floating in the sky. Clouds form when warm, moist air rises, cools, and the water vapour it carries condenses onto tiny particles into droplets too small to fall.
Key things to understand
- Air always holds some invisible water vapour, and warm air holds more of it than cold air.
- When moist air rises and cools, the vapour condenses onto tiny dust or salt particles, forming droplets — a cloud.
- The droplets are so small and light that rising air keeps them aloft.
- When droplets merge and grow heavy enough, they fall as rain, snow, or other precipitation.
- Cloud shapes and heights — fluffy cumulus, layered stratus, wispy cirrus — hint at the coming weather.
People also ask
How do clouds form?
Warm, moist air rises and cools. As it cools, the water vapour in it condenses onto tiny particles into droplets, and billions of these droplets together make a visible cloud.
Why do clouds float if they're made of water?
The water droplets are extremely tiny and light, and rising air currents hold them up. Only when droplets combine into bigger, heavier drops do they fall as rain.
Why are clouds white or grey?
Clouds scatter all colours of sunlight, so they look white. A cloud looks grey when it's thick enough to block the light passing through — often a sign of rain.
Part of the guide: Water & Weather Phenomena →