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What are clouds?

Clouds are tiny drops of condensing clear water vapor and/or ice crystals that settle on dust particles in the atmosphere. Clouds can be many different shapes and sizes. Some clouds are big and puffy on warm days, and other clouds bring precipitation, such as rain, hail, snow, sleet, and freezing rain.


Why do clouds form?

Clouds are merely the clumping of condensing water vapor. Moist air near the Earth’s surface is raised from the ground to high in the atmosphere either by the heat of the sun or by a colder invading air mass, called a cold front, that pushes the warm, moist air upward. When the air is lifted, both the air pressure and temperature drops. As soon as the air temperature reaches the air’s dew point, the water vapor in the moist air condenses, and clouds form.


Why are clouds white if water is clear?

Well, to understand this concept, one must know why the sky is blue. The rays from the sun have all of the colors in the visible color spectrum in them, so the rays appear to be white. This “white” sunlight passes through the Earth’s atmosphere, and the tiny airborne molecules, such as nitrogen particles, scatter the light from the blue part of the color spectrum. The molecules scatter the blue light until it is evenly distributed. The other colors in the spectrum reach the Earth’s surface with no interference, so their color isn’t distributed throughout the sky. Therefore, the sky appears to be blue.

Clouds are white because the water droplets are bigger than the particles that scatter the blue light in the sky. The clouds scatter and reflect all the visible colors of light that strike them. Since the visible colors of the sun appear to be white, the clouds that reflect that light must be white too. So clouds are white because they reflect the white light from the sun.


What about those dark black clouds before a storm?

In some cases, if the cloud is super thick or filled with a lot of water molecules, sunlight cannot pass through the cloud. Therefore, clouds can appear very dark because of the lack of sunlight shining through.


What kinds of clouds are there?

There are three main types of clouds. They are called cirrus, stratus, and cumulus clouds. There are many other kinds of cloud names, such as altocumulus and nimbostratus, that get their names from a combination of two kinds of clouds or some other factor.


This diagram shows various types of clouds, their relative location in the atmosphere, and a picture of what they look like.


Cloud Type Appearance Altitude
Cumulonimbus Thunderheads Near ground to 50,000 ft.
Cirrostratus Thin, wispy Above 18,000 ft.
Cirrus Very thin Above 18,000 ft.
Cirrocumulus Small puffy clouds Above 18,000 ft.
Altostratus Thin and uniform 6,000 to 20,000 ft.
Altocumulus Medium-sized and puffy 6,000 to 20,000 ft.
Stratocumulus Flat bottom, puffy top Below 6,000 ft.
Cumulus Puffy clouds Below 6,000 ft.
Nimbostratus Dark rain clouds Below 6,000 ft.
Stratus Uniform, layered clouds Below 6,000 ft.

To learn a little about the three basic kinds of clouds, click on the links below.

Cirrus Clouds

Cumulus Clouds

Stratus Clouds



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