The types of clouds are based on what they look like and how high are they in the sky. Based on this, we have 4 major divisions. They are :
1. High level: They are formed in altitudes more than 20,000 feet. Because the temperatures are very cold at these high elevations, these clouds are mainly composed of ice crystals. High level clouds are further divided in to three main parts:
Cirrus: They are very weak and thin clouds that are blown away by high winds. They usually mean that the day will have a pleasant and fair weather. These clouds flow in the direction of the winds at their altitudes.
Cirrostratus : They are very thin sheets of clouds extending over large parts of the sky. They are composed of ice crystals and are very difficult to detect. They sometimes signal the beginning of a warm front. These clouds do not show any precipitation.
Cirrocumulus: They look like small cotton puffs in the sky. They are sometimes known as Mackerel cloud due to their resemblance with the fish scales. Like other cumulus clouds, they also signify convection. Unlike other high level clouds, they include a small amount of water droplets but in a super cooled state. They do show precipitation but occasionally.
2. Mid level: They are found in altitudes between 6500 to 20000 feet. They are mainly composed of water droplets but can also be composed of ice crystals when the temperature is cold enough. They are further categorized as under:
Altocumulus: They are grey and puffy clouds which are largely composed of water droplets. These are usually seen on warm and humid summer mornings and are usually a sign that thunderstorms will follow later in the day. It also signifies convection as all the cumulus clouds do. They usually show no precipitation.
Altostratus: These are types which are uniform gray to bluish gray in color but slightly lighter than the nimbostratus ones. They are formed by the rising of a large air mass that condenses into a cloud. They are composed of ice crystals and water droplets and have the capacity of covering the entire sky. Rain is only possible in case of thickened clouds and if the rain persists, they are known as nimbostratus clouds.
3. Low level: They are found below 6500 feet and although they are mainly composed of water droplets, they can be composed of ice crystals if the temperatures are very cold in that region. They are further classified as :
Stratus: They belong to the class characterized by horizontal layering with a uniform base. The term stratus is used to describe flat, hazy and featureless clouds of low lying altitude which are dark grey to white in color. They can be the result of fog lifting in the morning. They usually show light precipitations.
Stratocumulus: They are characterized by large dark rounded masses. They appear much like cumulus ones except they are lumped together and are bigger. They show precipitation but not that intense. They may indicate a coming storm.
Cumulus: They are also known as fair weather clouds and look like floating cotton. They have flat bases and are not very tall. They are often precursors of other types. They have a noticeable vertical development and have well defined edges. They may appear alone, in lines or in clusters.
Nimbostratus: They are dark grey clouds that produce falling rain or snow. It has a moderate vertical development. It usually has a thickness of around 2000 meter and are found commonly in the middle latitudes.
Cumulonimbus: They can take up to several miles across the sky and can reach elevations of 39,000 feet or higher because of very strong up drafts in the atmosphere. Low level cumulonimbus are made of water droplets but at higher altitudes, they are composed of ice crystals. They are the types that bring lightening, thunder, violent tornadoes and other intense weather situations.