|MadSci Network: Earth Sciences|
Cloud formation is caused by several things, but generally, clouds are caused by air cooling and moisture condensing into the air, forming a cloud. This can be very rapid! In a thunderstorm, warm air moving up can form into a cloud in less than one minute. Other types of clouds, located very high in the atmosphere and made mostly of ice, can take minutes to hours to form depending on how fast the air moves up.
I've listed several web sites below that have some really good information
on the cloud formation process:
Try the links in the MadSci Library for more information on Earth Sciences.