Clouds are visible accumulations of tiny water droplets or ice crystals in the Earth's atmosphere.
The Process
Clouds form when water vapor, an invisible gas, turns into liquid water droplets. This process is called condensation.
For condensation to occur, the air must be saturated with water vapor. This usually happens when warm air rises, expands, and cools. Cool air can hold less water vapor than warm air, so as the air cools, some of the vapor condenses onto tiny particles floating in the air called Cloud Condensation Nuclei (CCN).
These nuclei can be dust, smoke, salt from the ocean, or pollution. Without these particles, clouds would have a very hard time forming!
