The three types of clouds are cumulus, stratus, and cirrus.
More Info: There are three kinds of clouds: cumulus, stratus, and cirrus. Clouds are essentially huge packets of air filled with condensed water vapor. The Earth’s surface is continually heated by the sun, causing packets of humid air to rise into the upper atmosphere and cool. As the air cools, the water vapor condenses into liquid water and a cloud is born (1). Clouds are classified based on their altitude and shape.
Cumulus clouds are the billowing, fluffy clouds often seen on summer days. They hover low in the atmosphere at less than 6,500 feet and contain huge volumes of condensed water droplets. The Latin root nimbus- is used to label clouds, which produce precipitation. Therefore, a cumulonimbus is a cumulus cloud that is producing precipitation (2). Cumulonimbus clouds are also known to produce thunderstorms.
Stratus clouds are the flat, gray blanket type clouds that fill the sky on overcast days. Like cumulus clouds, stratus clouds move low to the ground and contain lots of condensed water. The Latin root alto- means middle, and designates a low-level cloud that has risen into the middle atmosphere. Therefore, altostratus and altocumulus clouds are low-level clouds that have risen into the middle of the atmosphere, between 6,500 and 20,000 feet (3).
Cirrus clouds are thin, wispy and transparent. They form above 20,000 feet, in the coldest part of the atmosphere, and are made mostly of ice (4). If cirrus clouds form into solid sheets they are labeled cirrostratus, and if they form into blotchy, cellular rows, they are labeled cirrocumulus. Although there are three main cloud shapes, many of the shapes and Latin roots can be combined to form a total of ten cloud designations (5).
(1)2 University of Illinois
(3) National Weather Service
(4) National Weather Service National Forecast Office
Cloud Classification and Characteristics