The collection of water droplets or ice crystals suspended in the air, which forms when the air is cooled to its dew point and condensation occurs.

Wool-pack clouds with patches or rolls of cloud joined together in a kind of sheet.

Pale, water clouds that form a translucent veil over the sun.

High level cumulus clouds combined with cirrus clouds, indicating unstable air.

High, thin clouds that blanket the sky in ill-defined sheets.

From Latin for "curl"; they are wispy curls, like locks of hair.

These clouds are found high up in the atmosphere where water vapor is less abundant. Cirrus clouds consist mainly of ice crystals and are shaped by high-level winds.

Tall clouds with anvil-shaped tops that can herald or indicate storms.

Latin for "heap", they are heaps of separated cloud masses with flat bottoms and cauliflower tops.

These lumpy towers of clouds are usually found at low levels, below 6,500 feet and they are formed by updrafts of air, or thermals.

Low, dark, thick clouds of undefined shape; usually indicating heavy precipitation.

Latin for "rain", they are clouds that generate precipitation and are generally low clouds, less than a mile high.

While most clouds dwell in the first six miles above the ground, noctilucent clouds form about 50 miles (80.47 kilometers) up, near the top of the mesosphere, where temperatures plunge to a frigid minus 130 degrees Fahrenheit (54 degrees Celsius).

Composed of ice crystals, bright, silvery noctilucent clouds are visible at night because their height above the earth allows them to escape the planets' shadow.

Low, lumpy cloud layers with patches of blue sky between the cloud elements.

Latin for "layer"; they are layers or banks of clouds wider than they are thick.

Such clouds are formed by widespread uplifts of air and tend to be gray and cover most of the sky. They are often accompanied by mist and drizzles.