Trinity of Cloud Formation

The Trinity of Cloud Formation:

1 Warm Air

2 Dust

3 Water Vapor


All air contains water, but near the ground it is usually in the form of an invisible gas called water vapor. When warm air rises, it expands and cools. Cool air can't hold as much water vapor as warm air, so some of the vapor condenses onto tiny pieces of dust that are floating in the air and forms a tiny droplet around each dust particle. When billions of these droplets come together they become a visible cloud.
http://www.weatherwizkids.com/cloud.htm