A big part of the Earth is covered with bodies of water like oceans, seas, rivers and lakes. When the sun shines, these bodies of water become warm. Part of the warm water evaporates or changes in a gaseous vapor. Water also evaporates from plans and people. When water evaporates, it goes up into the air. Warm air can hold much water vapor.

Up in the air are tiny particles of dust, soot pollen and bits of salt from the ocean. As warm moist air rises, it begins to cool. The water vapor it carries condenses on the tiny particles in the air, and changes into droplets of water. Billions of the tiny water droplets form a cloud. Some clouds are made up of ice crystals. These are the clouds that form high up in the sky where air is very cold. The droplets of water from clouds fall as rain or snow when they become too heavy and the air can no longer hold them. Did you know that on very cold days, we can make clouds without even knowing it? When we breathe out warm, moist air, it cools in front of us and forms a little cloud which disappears quickly.

Kinds of clouds. Observe the sky today. Do you see many clouds? Do they have different shapes? Do they look near or far from the Earth? There are three main cloud shapes, stratus, cumulus, and cirrus.

Stratus clouds appear as layers or flat sheets. These clouds usually bring rain or snow.

(Stratus cloud) Image via Wikipedia

Cumulus clouds appear as piled-up masses of white fluffy cotton. Generally, these clouds are signs of fair weather, unless heavy with moisture. Cirrus clouds are thin, hair-like clouds found high up in the sky. Slowly drifting cirrus clouds indicate fair weather, while rapidly moving ones indicate bad weather.

(Cirrus cloud) Image via Wikipedia

Clouds maybe grouped according to their altitude or their height above the ground. Low clouds include stratus and stratocumulus clouds. These clouds form less than 1800 meters above the ground. Stratus clouds cover the sky like a thick, even sheet, while stratocumulus clouds cover the sky as large, rounded masses. Stratocumulus clouds have light and dark areas and are not as even in thickness as stratus clouds. These clouds appear before or after a rain.

(Stratoculumos cloud) Image via Wikipedia

The middle clouds include altostratus, altocumulus and nimbostratus clouds which form from a height of 1800 meters to 6000 meters above the ground. Altostratus clouds form a thick white or sometimes grey sheet across the sky that often shows a patch where the sun or moon is.

(Altostratus cloud) Image via Wikipedia

Altocumulus clouds appear in different shapes. Nimbostratus clouds are usually grey. Most often, these clouds are not visible because of the rain or snow that falls from them.

(Nimbostratus cloud) Image via Wikipedia

The high clouds include cirrus, cirrostratus, and cirrocumulus clouds which are formed from ice crystals instead of water droplets. Cirrostratus clouds appear as thin sheets. If you look at the moon and it appears to have a halo, then there is a cirrostratus cloud around. It is this cloud that causes a halo to appear around the moon or even the sun.

(Cirrustratus cloud) Image via Wikipedia

Cirrocumulus clouds are transparent and look like fish scales. A cumulonimbus cloud can be as tall as 18,000 meters from the base. Lightning, thunder, heavy rains or tornadoes come from cumulonimbus clouds. In addition, a cumulonimbus cloud that is shaped like an anvil is called a thunderhead.

(Cumulonimbus cloud) Image via Wikipedia

Now, observe the clouds again. Can you identify the clouds by their shapes or their altitudes? Can you predict what the weather will be by the kind of clouds you see in the sky?