How Do Clouds Form?

Scientists define clouds as visible masses of droplets, frozen water floating in the Earth’s atmosphere that you can see from the ground. Clouds are not unique to Earth, and can exist on other planets and in space as well. When a cloud forms in space, it is known as an interstellar cloud, or a nebula.

Nephology is the study of clouds, and it is under the greater branch of meteorology. 

As the most basic level, clouds form when moist air and cold, dry air combine. Specifically, three components are necessary for clouds to form: water vapor, cool or cold air, and condensation nuclei. Condensation nuclei are particles of dust or dirt that are in the air. This dust might come from volcanoes, cars, or fires to name a few sources.

When the temperature or the pressure decreases, this means that the air cannot physically hold as much water as it can in warmer weather. The lower the temperature is, the more condensation occurs. Condensation transforms water vapor into water droplets, or (depending how cold the air is) ice particles. The water molecules that are formed through this condensation collect on the surface area of the condensation nuclei, and a cloud is formed.

A white cloud means that the cloud was formed with warm air. A grey, or a black cloud, means that the cloud contains larger drops of water.  

Different Types of Clouds

There are three main types of clouds, although there are several subtypes. The three main types of clouds are:

• Cumulus - the white and fluffy clouds in the sky. Cumulus clouds are formed when warm, moist air rises quickly from the ground to the sky, and then cools off quickly. When this type of cloud turns grey or dark, they can result in rain, hail, or lightening. Further, when their color changes, these clouds are then referred to as cumulonimbus clouds. Cumulus clouds are usually found below two thousand meters high in the sky.
• Stratus - the flatter clouds that stretch over greater lengths of distance in the sky. Stratus clouds usually last longer than cumulus clouds, and they can also result in rain. This type of cloud results in the longer and steadier rain, while cumulus clouds might result in the heavier, but shorter periods of rain. However, stratus clouds do not usually result in precipitation. When stratus clouds turn grey, they are then referred to as nimbostratus clouds. Stratus clouds form below two thousand meters high in the sky.
• Cirrus - clouds which are extremely high in the sky, and are very light looking. Cirrus clouds are formed entirely from ice crystals. The clouds are so thin that sometimes it is difficult to tell one cirrus cloud from another. When this occurs, the mass of cirrus clouds are referred to as cirrostratus clouds. Cirrus clouds are located above seven thousand meters in the sky. Cirrus clouds signal a change of weather in the future, or they might indicate that a storm just took place.       

Fog

There is no difference between how clouds are formed and how fog is formed. Some scientists classify fog as a cloud that is in contact with the ground. Fog requires all the same ingredients (water vapor, cool air, and condensation nuclei) that clouds require to be formed.