text: Warm air in the atmosphere tends to rise, as a result of is lower density.  Warm air is also able to hold more water vapor in it than cooler air.  As the air rises, it cools due to adiabatic expansion, until it reaches the saturation point -  the temperature at which it can no longer keep any more vapor in it.  The moisture condenses out of the air and forms the clouds.\n\nFor some online sources on cloud formation, check these sites.