Notes

　General Classification.
Rain, Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then precipitated—that is, become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.
　Description.
"How Rain Is Formed"
The oceans are the chief source of rain, but lakes and rivers also contribute to it. The Sun's heat evaporates the water. It remains in the atmosphere as an invisible vapor until it condenses, first into clouds and then into raindrops. Condensation happens when the air is cooled.
Air cools either through expansion or by coming into contact with a cool object such as a cold landmass or an ice-covered expanse. When air passes over a cold object, it loses heat and its moisture condenses as fog, dew, or frost. Air also cools as it rises and expands. The water vapor in the cooling air condenses to form clouds and, sometimes, rain.
Air rises for several reasons. Convergent lift occurs in cyclonic stormssuch as tornadoes. Air whirling toward the center of a cyclone collides with itself and is forced upward. In convective lift, air coming into contact with a warm surface, such as a desert, is heated and becomes more buoyant than the surrounding air. In orographic lift, the air is forced upward as it encounters a cooler, denser body of air or when it meets raised landforms such as mountains.
For raindrops to form there must be particulate matter in the air, such as dust or salt, at temperatures above freezing. These particles are called condensation nuclei. When the nuclei are cooled to temperatures below the freezing point, water condenses around them in layers. The particles become so heavy they resist updrafts and fall through the clouds. If the updrafts are particularly strong, as in a thunderstorm, the rain nuclei may become very large and fall from the cloud as hail. When the air temperature is at or below freezing all the way to the ground, the precipitation falls as snow.
"Types of Rain."
There are three common types of rainfall, all of which occur in the United Kingdom. All have the common theme of air being forced to rise.

As air rises it cools it cannot hold as much moisture as it could when it was warmer. Eventually the rising air reaches a point where it is 100% saturated, in other words it cannot hold any more water. This is called dew point, and it is above this point that condensation occurs.

Condensation is the process by which the water vapour (a gas) held in the air is turned back into water droplets (a liquid), which fall as rain.

Convectional rainfall

Very common in areas where the ground is heated by the hot sun, such as the Tropics. This is why those areas experience heavy rainfalls most afternoons. The United Kingdom does experience some convectional rainfall during the summer, particularly in the South East of the country.

Convectional rainfall occurs when:

The surface of the earth is heated by the sun.
The warm surface heats the air above it. Hot air always rises so this newly heated air does so.
As it rises the air-cools and begins to condensate.
Further rising and cooling causes a large amount of condensation to occur and rain is formed.
Convection tends to produce towering cumulo-nimbus clouds, which produce heavy rain and possible thunder and lightning.

Frontal rainfall

The United Kingdom experiences a lot of frontal rainfall, as it is associated with the movement of depressions over the country, which are described in more detail elsewhere in this topic.

Frontal rainfall occurs when:

Two air masses meet, one a warm air mass and one a cold air mass.
The lighter, less dense, warm air is forced to rise over the denser, cold air.
This causes the warm air to cool and begin to condense.
As the warm air is forced to rise further condensation occurs and rain is formed.
Frontal rain produces a variety of clouds, which bring moderate to heavy rainfall.

Relief rainfall

This is also called orographic rainfall, which is very common in the United Kingdom, especially on the West coast since the prevailing weather comes from that direction.

Relief Rainfall occurs when:

The prevailing winds pick up moisture from the sea as they travel across it, making the air moist.
The moist air reaches the coast and is forced to rise over mountains and hills.
This forces the air to cool and condense, forming clouds.
The air continues to be forced over the mountains and so it drops its moisture as relief rain.
Once over the top of the mountain the air will usually drop down the other side, warming as it does so. This means it has a greater ability to carry water moisture and so there is little rain on the far side of the mountain. This area is called the rain shadow.

"Effects of Rain"
Positive effects :
1. Plants can flourish.
2. The soil will not dry out.
3. Earth to cool.

Negative effects :
1. Flooding.
2. Disturb people to activities, like when I went to school I was hindered by rain.
3. Can cause flu and fever.
4. Rainwater can cause itchy skin.

That's positive effects and negative effects of rain in my opinion. May be understood.

GOD has made earth with very very beautiful and so perfectly formed. But we have to preserve this earth together, In order to remain sustainable earth.