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What Causes Rain Clouds?

Rain clouds are a constant occurrence throughout the world and the main process in which water is recycled throughout the planet. All of the water on the planet continually cycles through this process by means of evaporation and precipitation. The Weather Questions website states that "at any given time, precipitation covers only about 2 percent to 5 percent of the surface of the Earth, while evaporation is occurring over the remaining 95 to 98 percent of the Earth." Several factors are needed to carry out this process.

Water Vapor
- Water can exist in three forms; solid, liquid and vapor. Water vapor is essentially a gaseous form of water, and it exists in all air to some extent up to about 4 percent in warm, humid tropical air. Concentrations of water vapor within the atmosphere are higher in warmer climates and lower in arid or very cold climates. Clouds need higher concentrations of water vapor within them to create a greater chance for precipitation, or rain.
Cloud Formation and Rising
- Several factors can influence the formation of clouds along with the water vapor content, such as seasonal variations, mountain ranges, nearby bodies of water and heat. Once warm air with sufficient water vapor forms, the cloud will start to rise within the atmosphere. Once this happens, it is dependent on the amount of water vapor joined with other factors whether precipitation will occur.
A Cooling Cloud
- Warm masses of air have the capability of holding more droplets of water vapor than cooler masses of air. As a formed cloud rises within the atmosphere, the mass of air will start to cool down. As the cloud becomes cooler the water vapor within it will begin to condense and form together. This will create the characteristic darker look of a cloud, giving it the gray to black look and bringing the cloud closer to the possibility of rain.
Gravity
- When water becomes too heavy, it falls to the ground.
  
  The final factor in a cloud creating rain is gravity. As the water vapor inside the cloud mass rises and cools, bigger droplets of liquid water begin to form. This can happen from vapor condensing into droplets from the cooling of the air as well as two droplets forming together to form a bigger and heavier droplet. When the conditions within the cloud can no longer keep the droplets of water aloft, gravity will cause them to fall toward the Earth.

Nature