Clouds may contain water in a gaseous, liquid and solid form but primarily consist of water vapor, which is a gas. Clouds form when water condenses into liquid droplets around dust, ice or other airborne particles, causing the water vapor in the air to become visible.
Condensation occurs when air becomes cool enough to cause water vapor to become saturated and take form as a liquid. Atmospheric conditions, such as wind speed and temperature, determine the type of cloud that is formed. The particles around which water vapor condenses are known as condensation nuclei. When ice crystals or water droplets become too heavy for suspension in the air, they fall to the Earth's surface as rain or snow.