Convectional Rain

• Sometimes, rain is caused by what is known as "convection." The sun heats the ground and the moist air directly above it. Since hot air is less dense than is cold, the heated air will attempt to move to a higher elevation, and if the air pressure is low enough, will succeed in doing so. The air will eventually cool, and the moisture in it will condense, forming cumulus and cumulonimbus clouds. These are what most often result in short rain showers.
  
  

Relief Rain

• A second way rainclouds can form is by relief. Air is blown by wind into a mountain range or hilly area, and is forced to rise. This cools the air and causes any moisture in it to condense, forming thick clouds with drizzly rain. If the mountains are high enough, the clouds will not be able to blow over their tops, and will release all their ran on the windward slopes. The other side of the range will get little rain, and will likely be dry and barren, resulting in what is known as a "rain shadow."
  
  

Frontal Rain

• Frontal rain is caused by the meeting of cold and warm bodies of air. The warm air is pushed upward, though whether this happens quickly or slowly depends on which body is moving faster. If the warm air meets the cold, it results in a warm front, in which the warm air slowly rises and condenses. The clouds thus formed will slowly descend, passing through cirrus, stratus, and nimbostratus forms until they release a slow, steady rain. If the warm air is the stationary participant, a cold front results, and the warm air quickly rises into cumulonimbus clouds, often causing a thunderstorm.
  
  

Monsoon Rain

• Seasonal in nature, monsoon rains are the result of the reversal of air rotation. The land becomes warmer than the sea as the angle of the Earth in relation to the Sun changes, and warm air is swept inland from the sea. This air rises, and, having gathered moisture during its sea-passage, forms clouds, causing a six-month rainy season.
  
  

Rain Release

• No matter how the clouds formed, the cold air causes the moisture to condense, forming larger and larger droplets. Near-microscopic cloud drops collide and join together in a process often hastened by air movement. These drops increase in size until they fall under the influence of gravity and descend as rain.