At any one time, there can be a number of types of clouds in the sky. Here you can see puffy cumulus clouds set against cirrus clouds.
Image credit: Nicholas_T

What Are Clouds?
Clouds are large groups of tiny water droplets (vapor) or ice crystals that cling to pieces of dust in the atmosphere.

Clouds are so important to the earth’s weather that meteorologists (people who study the weather) also study the clouds and their movement. In fact, without clouds it wouldn’t rain or snow! They come in all different shapes and sizes. Some are really low to the ground and some are way high up in the sky.

Scientists have developed a system to classify the different types of clouds. Each cloud you see can be put into one of the many categories based on both their general shape and how high up they are in the atmosphere.

Thin sheets of cirrus clouds
Image credit: PiccoloNamek

Cirrus Clouds
These are the highest clouds in the atmosphere. Cirrus clouds are thin, wispy clouds that often appear on days with fair weather and low winds. In fact, the word cirrus means “curl of hair” in Latin!

Because of the freezing temperatures high up in the atmosphere, these clouds are usually made up of ice crystals which give them a bright white appearance.

These clouds form in flat sheets, so they aren’t as thick as the other types of clouds. Cirrus clouds are also spread out in patches, with large breaks of sky in between them.

Since these clouds are so far from the ground, they aren’t often affected by the changing weather on the earth’s surface. Instead, they peacefully float along from west to east.

Cumulus clouds over a field
Image credit: PiccoloNamek

Cumulus Clouds
Cumulus clouds are bright white and look like big puffs of cotton. The word cumulus is Latin for “heap” or “pile.” This is because these clouds are sometimes extremely thick and tall and they often grow in upward direction. An easy way to remember this is to think of the word accumulate, which means “to gather an increasing amount.”

The bases of these clouds are often flat and the tops are usually composed of rounded sections. Cumulus clouds are vertically developing clouds which means they can become extremely tall clouds.

Stratus Clouds over Hardangervidda, Norway

Stratus Clouds
Stratus clouds are thick, gray clouds that look like fog that hasn’t touched the ground. In fact, these clouds sometimes are made up of fog that has lifted from the ground. As you may have guessed, these are low-altitude clouds, which means they are really close to the ground.

When someone says, “today is a gray and cloudy day”, they are usually referring to these thick, uniform clouds. Stratus clouds often produce a light, drizzly rain or snow, especially when it’s a nimbostratus cloud.

Nimbus Clouds
The word “nimbus” means rain in Latin, so these are the clouds that produce rain. Any cloud with the prefix “nimbo” or the suffix “nimbus” is a type of rain cloud. For example, a nimbostratus cloud is a stratus cloud that will cause rain or snow. Since stratus clouds are dull, gray, and featureless, nimbostratus clouds can be seen on gray, rainy days.

Another type of rain cloud is the cumulonimbus. Since cumulus clouds are the heaping, giants, cumulonimbus clouds are giant, heaping rain clouds. These clouds can be so huge that their bases start at only 1,000 feet above the ground with a top of 39,000 feet! These clouds, sometimes called thunderheads, form into the shape of an anvil which is a sure sign of a storm!

Heavy thunderstorms and even tornadoes are associated with this type of cloud (a tornado is a rotating column of air connected to a cumulonimbus cloud.)

A cumulonimbus cloud near White Canyon, Utah

Disintegrating stratocumulus clouds
Image credit: LivingShadow

Mixing It Up: Cloud Subtypes
You may have noticed from the last section on the different kinds of nimbus clouds, that different clouds types exist beyond just cirrus, cumulus, stratus, and nimbus. You’ve learned about nimbostratus and cumulonimbus clouds, so let’s go over some of the other kinds.

Most clouds can be described by mixing and matching the terms cirrus, cumulus, stratus, and nimbus. For example, there are cirrocumulus clouds which are vertically developing (and blotchy) clouds way high up in the atmosphere.

Cirrostratus clouds are thin, wispy sheet clouds. What’s cool about these clouds is that they can cause a halo-like appearance around the sun or moon! This is caused by the light refracting through the cloud’s vapor.

There aren’t any clouds called cirronimbus or nimbocirrus. This is because cirrus clouds seldom rain. When they do rain, it’ll drop tiny ice crystals that will evaporate before they hit the ground.