Cirrus clouds
These wispy clouds usually form above 18,000 feet. Cirrus clouds
generally move from west to east. They form when water vapor forms ice
crystals, and they are so thin because of the height at which they form. There is
very little water vapor above 18,000 feet, and so big thick clouds cannot form.
These are the three main types of clouds that can form; however, there are
also several combination clouds.