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Table of Contents
What are clouds?
Clouds are water droplets or ice crystals that have formed on tiny bits of dust and dirt in the air. When we look up into the sky, we can see many different types of clouds. They form in the troposphere, which is the layer of atmosphere closest to the Earth’s surface.
Download a poster showing all different types of clouds
There are more than 100 different types of clouds but most people are familiar with just 10.
These 10 cloud types are grouped into low, middle, or high lying clouds. They can each tell us about the weather.
Clouds are classified not only by their shape and appearance but also by the altitude at which they form. This is measured as the height above sea level to the base of the cloud.
What are the different types of clouds?
Low lying clouds (below 6,500 ft (1,981 m))
Cumulus (1,200-6,500 ft) are the big, fluffy clouds you see in an otherwise blue sky. They are the type of clouds children draw in pictures. They are fair weather clouds, forming when the sun heats the ground directly beneath it.
Stratus (0-2,000 ft) are the clouds that blanket over the sky on an overcast day. They don’t have any distinctive shape. They usually mean mist or drizzle.
Stratocumulus (1,200-6,500 ft) as the name suggests, are a mixture of stratus and cumulus. They are flattened cumulus clouds. You can often see blue sky between them. They indicate a change in weather. These clouds don’t usually cause rain, but their presence can be followed by rain.
Middle lying clouds (between 6,500 and 20,000 feet (1,981–6,096 m))
Altocumulus (7,000-18,000 ft) clouds look like sheep’s wool. They have a similar shape to stratocumulus but are smaller because they are higher up. They are seen on warm days but can mean cold weather is on the way.
Nimbostratus (2,000-10,000 ft) are typical rain clouds. They are often dark gray and cover the whole sky. They appear baggy or sagging. They mean rain or snow is falling or is on the way.
Altostratus (6,500-20,000 ft) clouds can look like a blanket of mist over the sky. Usually, they are thin enough for you to see the sun through them. They are found ahead of a warm or occluded weather front.
High lying clouds (above 20,000 feet (6,096 m))
Cirrus (20,000-40,000 ft) are distinctive white whisps in an otherwise clear sky. The name “cirrus” means “curl of hair.” They are made of ice crystals because they are formed so high up. Although they signify fair weather, they are often found before a storm or cyclone. These are a warning sign of nor’easters, storms that occur on the east coast of North America.
Cirrocumulus (20,000-40,000 ft) look like white ripples or fish scales across the sky, giving the description “mackerel sky.” The cloudlets are made of ice and cold water. They are fair weather clouds but often prelude a storm.
Cirrostratus (20,000-40,000 ft) clouds look like a thin layer of semi-transparent mist covering the sky, through which the sun can be seen. Often you see a halo around the sun when cirrostratus clouds are in the sky. They are associated with warm weather arriving.
The only cloud type that spans low, middle, and high altitudes is
Cumulonimbus. These are huge fluffy clouds that look a bit like cumulus clouds. They are thunderstorm clouds, so they are associated with stormy weather.
How are clouds formed?
Clouds are formed from processes called condensation and deposition. Water in the environment, such as in a river, lake, or sea, heats up under the warmth of the sun. When water molecules are heated, they turn from a liquid to a gas during a process called evaporation. Water in the form of gas is called water vapor. This gas is invisible, and the water molecules are carried off into the atmosphere.
The atmosphere can only hold a certain amount of water vapor. Warmer climates can hold more water in the air than colder climates. If the temperature or atmospheric pressure of the air changes, the water vapor turns back into water via the process of condensation, or directly into a solid (ice) via deposition.
The water vapor condenses onto tiny particles in the air. These particles can be dust, dirt, or sea salt floating in the atmosphere. They provide a surface for the water vapor to condense on to. The resulting droplets or ice crystals accumulate together and form a cloud. Unlike rain droplets, cloud droplets are tiny and very light, so they float in the air.
How important are clouds?
All different types of clouds serve a very important purpose.
They significantly affect the warmth of our planet. They do this in two ways.
During the daytime, they protect us from the sun’s heat. Clouds block about 20% of the sun’s heat and help absorb incoming solar radiation.
During the nighttime, they keep us warm with a blanketing effect. They partially absorb heat that is released as the ground cools at night. This heat is then radiated back to the earth’s surface.
Clouds also water our lands. We associate clouds with some form of precipitation, either rain or snow. Clouds absorb and release moisture in a remarkable way. They are an integral part of the water cycle and provide water for plants and animals. This means they are essential for life on earth.
Due to their composition, clouds also move atmospheric particles around the earth. This includes dust, dirt, and bacteria. Wind helps to spread these around. It’s fascinating to think that some of the dirt in your back yard may have originated from Africa. In fact, most of the topsoil in the Caribbean is made up of dust from Africa.
The formation of clouds is a delicate balance of evaporation and condensation. Changes in our climate could affect these processes and ultimately impact cloud formation. This would be disastrous for the planet as they are such an important feature of the natural world.
Troposphere: the lowest level of atmosphere on earth
occluded weather front: the merging of a warm and cold weather front
condensation: the change in the state of matter from gas to liquid
deposition: the change in the state of gas directly into solid, without turning into liquid first
evaporation: the change in the state of matter from liquid to gas below boiling point
atmospheric pressure: the weight of air in the atmosphere
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