Here is how clouds are formed: Warm air, laden with moisture, rises into the sky. When it gets to certain height, the warm air cools. At the cooler temperature it can no longer hold all its moisture in the form of water vapour. So the extra moisture changes into small drops of water, or bits of ice, and this forms clouds.No two clouds are exactly alike, and they are always changing their shape. The reason we have different types of clouds is that cloud formation takes place at different hights and temperature. And clouds will be composed of different particles, depending on their height and temperature.
The highest clouds are called "noctilucent" clouds. They may be up as high as 30 to 50 miles! The next highest are called "nacreous", or "mother-of-pearl" clouds. They're 12 to 18 miles high. They are very thin, beautifully colored clouds composed of dust or waterdrops, and they are seen only after sunset, at night, or before sunrise.
The next highest clouds, which are five or more miles above the earth, are called "cirrus" clouds, "cirrostratus" clouds, and "cirrocumulus" clouds. The cirrus are feathery and threadlike, the cirrostratus are thin, whitish sheets, and the cirrocumulus are small, round clouds which form "mackerel" pattern in the sky. All these clouds are made up of tiny bits of ice.
Lower clouds are made of little drops of water. The highest of these, the altocumulus clouds, are about two to four miles above the earth, and are made of larger, rounded masses than the cirrocumulus clouds. At the same levels are the altostratus clouds, which often cover the whole sky with a greyish veil through which the sun and moo shine as spots of pale light.
Lower still, about a mile high, are the stratocumulus clouds, large and lumpy. At the same level are the rain clouds, the nimbostratus, thick, dark, and shapeless. Very low, less than 610 metres above the ground, are the stratus clouds, which are sheets of high fog. Two other kinds of clouds, the cumulus, and the cumulonimbus, are the big, fat, "cauliflower" clouds that bring thunder and storms.