How do clouds form?

Basically clouds form when water vapour rises upwards in the air, and condenses above the surface of the Earth. The formation of cumulus clouds can be triggered in response to a wide range of weather conditions prevailing on the planet. These clouds form during fair weather as well as just before storms. In fact, cumulus clouds are precursors of various other types of clouds, including heavy clouds, such as cumulonimbus clouds. These clouds tend to form quite close to the surface of the Earth, however, their tendency of vertical development can make them huge and eventually convert them to thunderstorms if they continue to get required amount of rising air. The height at which these clouds form can range between 8,000 ft to 20,000 ft, depending on the amount of moisture content in the rising air. Basically, higher humidity would mean lower cloud base.

Though, no two clouds are the same, clouds can still be categorized into different classes. Based on certain features, clouds are divided into four main types: High level clouds, medium level clouds, low level clouds and vertical clouds. 

Low Level Clouds. 

Low level clouds comprise water droplets and are found below 2,000 meters. These types of clouds even comprise snow and ice particles, during cold temperatures. The different types of low level clouds are as follows:

Stratus Clouds: These cloud types are low altitude clouds that appear grayish in color from the ground and cover the expanse of the sky. The word 'stratus' is a Latin word meaning 'spread out'. These clouds look like a gray blanket spread over the sky and are commonly seen in coastline and valley regions. These clouds are responsible for bringing rain or snow. When a thick fog lifts, it leaves low stratus clouds behind. 
Cumulonimbus Clouds: Cloud types conducing to heavy thunderstorms in summer months are another version of cumulus clouds and are called cumulonimbus clouds. These clouds are rain clouds which may extend 10 km above the ground and 10 km across the skies. The word cumulonimbus in Latin means "column rain", which is why these rain bearing clouds have been given this name. Unlike its cotton ball relative the cumulus clouds, these clouds bear semblance to a huge cauliflower of bulging turrets. 

Nimbostratus Clouds: These clouds get their name from the two Latin words 'nimbo' meaning rain and 'stratus' meaning 'spread out' or 'layered'. These are rain clouds found forming uniform layers of shapeless 2,000 meter thick, dark gray clouds. Oftentimes, they blanket the entire sky and conduce to continuous snow or rainfall.

Middle Level Clouds.

These types of clouds are found floating between 2,000-6,000 meters above ground level. Middle level clouds comprise water droplets as well as ice crystals during low temperatures. The different types of middle level clouds are as follows:

Altocumulus Clouds: Altocumulus clouds are formed in groups, so you can say that these are social clouds! The clouds appear like grayish-white puffy masses, with one portion of the cloud darker in shade than the other. They may even appear rolled out in parallel bands or waves. Presence of altocumulus clouds on a warm, humid summer morning oft indicates the possibility of thunderstorms by late afternoon. 
Altostratus Clouds: These are grayish or bluish-gray clouds comprising water droplets and ice crystals. These clouds get their name from two Latin words 'alto' meaning high and 'stratus' meaning layered or spread out. These dark clouds blanket mostly the entire expanse of the sky and oft are formed just before storms.

High Level Clouds.

These types of clouds are formed above 6,000 meters of height, as the temperatures at high elevations are very low and adequate for ice crystal formation. At times, when the sun is low in horizon, these thin, white clouds appear in breathtaking arrays of colours. 
Cirrus Clouds: Cirrus clouds are white clouds formed at a height of 7,000 meters and help predict fair weather. Their faint, feather-like appearance gives them their name, which comes from the Latin word 'cirrus' meaning 'curl of hair'. Cirrus clouds comprise entirely of ice particles and adorn the sky in the form of shadowy, thin, mare's tale like clouds. 
Cirrocumulus Clouds: These small fluffs of clouds appear in long rows between a height of 6,000-13,000 meters from ground level. Though usually white, these clouds may at times, appear gray and cover the sky in a way that makes it look like fish scales. This is why the sky covered with cirrocumulus clouds are called 'mackerel skies'. These clouds do not coalesce with other clouds to form larger cloud bodies. Observed mostly during winters, these clouds indicate cold weather. 
Cirrostratus Clouds: These clouds appear as thin uniform sheets of clouds, which permit visibility of the Sun or the Moon. In fact, thin cirrostratus clouds, even lead to the formation of a bright ring of light around the Sun or the Moon. This halo is the result of refraction of light emanating from them. Usually, the cirrostratus clouds indicate rain or snow storm, in the next 12-24 hours.

Vertical Clouds.

These clouds are formed at heights beyond 12,000 meters. Cumulus clouds are examples of vertical clouds. The floating, cotton ball-like clouds that we see in the sky are cumulus clouds. These types of clouds are characterized by sharp outlines and flat bases. They may even appear in light gray shades. Their fluffy appearance gave rise to their name from the Latin word 'cumulus', which means pile or heap. The puffy balls of cotton drifting across the skies with the breeze can result in light showers, rain or even snow. 

Weather can be predicted to a certain level by studying the clouds. Any planet of the solar system that has atmosphere will definitely have clouds. Besides Earth, clouds exist on other planets like Venus, Mars, Jupiter and Saturn as well. They are nothing but condensed droplets suspended in the atmosphere above the surface of the planet.

Processes of Cloud Formation 

Clouds are formed when the air in the atmosphere is so saturated with water vapour that it cannot hold any more of it. This may happen under two conditions viz., the air has cooled down to a point where condensation is bound to take place because the air has expanded enough and has lost a considerable amount of its moisture content. And the quantity of water in the atmosphere had increased to such an extent that the air has no capacity to hold any more of it. The amount of water in the atmosphere may rise due to factors such as evaporation. Though cloud formation may seem as simple as condensation of water vapour in air, in reality the entire process is much more complicated. For the water vapour to condense at a particular point and form clouds, the moist air that rises above the earth's surface has to undergo a series of processes. Clouds thus, may be formed in five different ways.

These include:

  • Heating of the Earth's surface

Heating of the surface of the Earth results in the formation of clouds.

When the ground heats up due to the heat of the Sun, it in turn heats the air around it.

This warm air due to heating thus reduces in density, and becomes lighter.

Because it becomes lighter, it begins to rise up in the atmosphere.

As it rises higher and higher into the atmosphere, it begins to expand, thus releasing the moisture content.

This released moisture content/water vapour begins to condense as the temperature goes on dropping at higher altitudes.

This condensed moisture from the air results in the formation of clouds.The clouds that are thus formed are predominantly cumulus, stratocumulus and cumulonimbus.

  • Hills, mountains and terrains.

The air that blows towards the mountains and other vertical landforms is forced to rise at high altitudes.

It thus expands, becomes cooler and begins to drain out its moisture content.

At considerable heights, this moisture content/water vapor begins to condense, thus giving rise to the formation of clouds.

The clouds thus formed are primarily lenticular clouds and stratus clouds.

  • Frontal

A front is a boundary that lies between warm air which contains some moisture content and cold air which is dry enough.

Frontal clouds are formed when two masses of air, each one of a different temperature, come in contact with each other.

Whether the mass of warm air is over the colder one or not, it expands anyway owing to the altitude at which it has risen.

Its expansion leads to its cooling and subsequent condensation of the moisture that escapes through. This condensation leads to the formation of clouds.

The clouds thus formed are cirrus, cirrostratus, altocumulus, stratocumulus, nimbostratus and stratus.

  • Convergence

When different streams of air flowing from different directions meet at a focal point, a sort of pressure is created at that point.

This pressure forces the air to flow in an upward direction, where all the streams flow alongside each other. In other words, they converge.

Again, like in all the other processes, the air cools, expands and lets out water vapour that condenses to form clouds.

This process primarily forms cumulus clouds and in some cases may give rise to small showers.

  • Atmospheric turbulence

Sometimes, turbulent weather conditions in the upper atmosphere pose as a hindrance in the way of free flow of air.This causes the air to flow in a circular pattern owing to the fact that it cannot flow on its designated track.When the warm air containing moisture rises up, and reaches the level where this atmospheric turbulence is happening, it cools down and the water vapor content in it condenses on the spot, thus forming clouds.The typical examples of turbulent clouds are cumulus and cumulonimbus.

Formation of clouds can sometimes cause a cloud field. Cloud fields are simply a group of clouds, which sometimes take on a strategic shape which has its own characteristics. The 'Open Cell' is a type of cloud field which resembles a honeycomb. It has denser clouds in the middle and clearer clouds at the end.

The colours of clouds also vary and impart important information about the weather. The characteristic white color of clouds means that they were formed with warm air which contained water vapor. The grey or black clouds are formed when the droplets in the cloud combine to make bigger droplets and this happens as the cloud matures. Clouds also sometimes appear in beautiful shades of blue, yellow and green. They get these colours due to the interplay of light and shade that takes place during different times of the day.