Clouds are an important part of the water cycle. The water cycle is the movement of water from the Earth into the sky and then back down to the Earth again. Over 70% of the Earth is covered in water! Water on the Earth is in the form of salt water (97%), which is water that is found in the oceans and saltwater lakes, and fresh water (3%), which is water that is found in rivers, ponds, lakes, streams, and underground.

The sun heats water on the surface of the Earth, and causes it to evaporate. Evaporation is the process when water moves from being a liquid to being vapor. Water vapor is made up of tiny water droplets in the air. Water can also move into the air through transpiration. Transpiration is the movement of water out of plants. During photosynthesis, plants make oxygen and water. Water then moves out of tiny holes on the leaves and into the air. The water vapor rises up into the atmosphere, and as it cools, it condenses. When the water vapor condenses it forms clouds. Precipitation occurs when so much water vapor condenses that the air cannot hold it anymore. The clouds get so heavy that some of the water must fall back down to Earth as rain, snow, sleet, or hail.

There are many different types of clouds. The type of cloud depends on how high up in the atmosphere the water condenses. Read about different types of clouds below! Click on each button for more info.

Stratus clouds occur below an altitude of 6,000 feet. These clouds look like flat sheets of clouds, and can mean an overcast or rainy day. These clouds are usually a uniform color of gray, and cover most of the sky without a lot of breaks.

Cumulus clouds also form below 6,000 feet and look like big fluffy cottonballs. They usually mean that the weather will be nice; however, sometimes they can get very tall and turn into thunderheads. These clouds are usually flat on the bottom, but have very lumpy tops. Cumulus clouds usually form alone, and there is a lot of blue sky between different clouds.

These wispy clouds usually form high in the atmosphere, above 18,000 feet. Cirrus clouds generally move from west to east. They form when water vapor forms ice crystals, and they are 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.

The three types of cloud above are the main types; but there are also combination clouds. Click each one below to read more!

These usually form below 6,000 feet, and usually form in rows or patches, with blue sky in between. The color of stratocumulus clouds can range from white to dark gray, but precipitation hardly ever falls from these clouds.

These also form below 6,000 feet and usually produce steady precipitation. Steady precipitation isn’t like a hard thundershower, but can instead last for several hours or even more than a day. Nimbostratus clouds are so thick that you can’t see the sun or the moon through them.

These form higher than stratocumulus or nimbostratus clouds - between 6,000 and 20,000 feet. Altostratus clouds cover the entire sky over a large area, and usually produce steady precipitation ahead of a storm. You can see a bit of the sun through the clouds, but the sun will be hazy or ‘watery’. Even though you can see the sun, altostratus clouds do not let enough sunlight through to produce shadows.

These also form between 6,000 and 20,000 feet. They look like puffy gray balls or blobs, and sometimes appear in rows. Part of these clouds is usually darker than the rest, and this helps to set them apart from higher cirrocumulus clouds. If you see these clouds on a hot summer morning it often means that there will be thunderstorms in the afternoon.

These form even higher than most altostratus and altocumulus clouds, at above 18,000 feet. These clouds are so thin that you can see the moon and the sun clearly. Sometimes you only know that there are cirrostratus clouds in the sky because you can see a fuzzy halo around the sun or the moon, caused when the ice crystals in the cloud bend the light from the sun and the moon. Cirrostratus clouds usually mean that there will be rain or snow within 24 hours.

These clouds also form above 18,000 feet. They can look like small rounded puffs or cotton balls, either alone or in rows. When the puffs are in rows, the sky has a rippling look, and this is how you can tell that they are cirrocumulus clouds, and not cirrus or cirrostratus clouds.

These clouds are thunderstorm clouds. The word "nimbus" or "nimbo" means precipitation-producing cloud.

Take the short quiz below to test your knowledge! Try your best to answer without looking above.


97% is saltwater and 3% is freshwater

It's the process where water moves from being a liquid to being a vapor.


The sun heats the water and causes the water to evaporate. Water also enters the air through transpiration. Water vapor moves through the air until it condenses into clouds. When so much water has condensed that the air cannot hold it any longer, water falls back to Earth as precipitation.

Stratus, cumulus, and cirrus

Cumulus clouds

Cirrus clouds

Nimbostratus clouds form below 6,000 feet and produce a steady form of precipitation. They are so thick that you can’t see the sun or the moon.

Cirrostratus clouds usually mean that there will be rain or snow in 24 hours, and either nimbostratus or cumulonimbus clouds will bring snow.

Photo Credits: Stratocumulus: By Nicholas A. Tonelli from Pennsylvania, USA - Drive-Through, CC BY 2.0,; Nimbostratus: CC BY-SA 3.0,; Altostratus: By The Great Cloudwatcher - Own work, CC BY-SA 3.0,; Altocumulus: By Bidgee - Own work, CC BY-SA 3.0,; Cirrostratus: CC BY-SA 3.0,; Cirrocumulus: By King of Hearts - Own work, CC BY-SA 3.0,; Cumulonimbus: By Pitero 86 - Own work, CC BY-SA 4.0,;