Look up at any cloud and ask where it came from. Clouds are made of tiny drops of water or tiny bits of ice, and 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. Clouds form when air rises and cools. Cloud drops form around tiny specks such as dust, pollen or salt.

Something has to lift the air. The Sun heats the ground, the warm air above it rises, and cumulus clouds can form. Cumulus clouds are puffy, lumpy clouds, and the name comes from a Latin word meaning heap or pile. They often show up on sunny days. Air pushed up a mountain cools and can make clouds too. Lenticular clouds are lens-shaped and often look like flying saucers.

A cloud does not drop its water right away, so let us follow the water out of a cloud. 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. Hail is solid balls of ice that fall from clouds. Nimbostratus clouds are dark gray clouds that bring steady rain or snow.

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. Altocumulus clouds are mid-level clouds that form in rounded clumps. Stratus clouds are low, gray clouds that can cover the whole sky like a blanket. These three groups run from the high ice clouds down to the low gray ones.

Some clouds grow very tall. Some cumulus clouds grow into storm clouds, and cumulonimbus clouds are thunderclouds. One cumulonimbus cloud can be about 10 kilometers (33,000 feet or 6 miles) tall. A tall thundercloud can flatten at the top into the shape of an anvil. Inside a storm there is lightning, and lightning heats the air around it to about five times hotter than the surface of the Sun.

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. Storms bring thunder, so it helps to know what thunder means and what to do about it. 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
• anvil: flat-topped shape
• lenticular: lens-shaped