Look up and you will see clouds. Clouds are made of tiny drops of water or tiny bits of ice. They look white because sunlight is white. Water vapor is the gas form of water, and it is in the air all around us. Clouds form when water vapor in the air turns into tiny drops of liquid water.

Cloud droplets are too small to fall as rain, so they float in the air. Rain falls when cloud droplets grow big and heavy enough to leave the cloud. Rain and snow fall out of clouds.

Clouds are sorted into high, middle and low groups by how high they are in the sky. Cirrus clouds are thin, wispy clouds high in the sky, and they are made of ice crystals. Cumulus clouds are puffy, lumpy clouds. Stratus clouds are low, gray clouds that can cover the whole sky like a blanket.

Some cloud names come from Latin. The name cumulus comes from a Latin word meaning heap or pile. Nimbus is Latin for rain, so a nimbus cloud is a rain cloud. Nimbostratus clouds are dark gray clouds that bring steady rain or snow. Cumulonimbus clouds are thunderclouds, and one can be about 10 kilometers (33,000 feet or 6 miles) tall.

Clouds can be clues about the weather. Cumulus clouds often show up on sunny days, and some grow into storm clouds. Thin cirrostratus clouds can warn that rain or snow may come within a day. They can also make a ring of light, called a halo, around the Sun or Moon.

Some clouds look odd. A sky full of small cirrocumulus clouds can look like fish scales, so it is called a mackerel sky. Lenticular clouds are lens-shaped and often look like flying saucers. The white streaks behind high-flying jets are clouds called contrails.

Thunder is the sound that lightning makes. You see lightning before you hear its thunder, because light travels faster than sound. To find how far away lightning is, count the seconds between the flash and the thunder and divide by 5 to get miles. When you hear thunder, go indoors, into a building or a car with a roof.

Words to know

• vapor: water as gas
• droplets: tiny drops
• nimbus: rain cloud
• halo: ring of light
• contrails: jet clouds

The short version

Clouds are made of tiny drops of water or tiny bits of ice. They form when water vapor in the air turns into tiny drops of liquid water. The drops are too small to fall, so they float in the air. Rain falls when cloud droplets grow big and heavy enough to leave the cloud.

Quick facts

• Clouds are made of tiny drops of water or tiny bits of ice.
• Clouds are sorted into high, middle and low groups by how high they are in the sky.
• A cumulonimbus cloud is a thundercloud and can be about 10 kilometers (6 miles) tall.
• Count the seconds between lightning and thunder and divide by 5 to get miles.