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.
Relief Rain:When a moisture bearing wind is obstructed by a mountain range, it is forced to rise along the slope. On rising, it cools to form a cumulonimbus cloud. Further cooling causes Relief rain. The windward side of the mountain barrier receives heavy rainfall. On the leeward side air gets warmer as it descends and hence very little rain falls. The leeward side of the mountain is called the rain shadow. This type of rain is received in the Indian subcontinent the south-west monsoon that blows in from the Arabian Sea. The Western ghats receive over 300 cm of rain. The Leeward side on the Deccan plateau gets hardly 60 to 70 cm of rain.Convectional Rain:This type of rain is common in the hot and wet tropical rain forests of central Africa, Amazon basin of South America and the islands of south-east Asia. Continuous heating of the earth in the day causes hot convectional currents to raise Water keeps on evaporating and rising up. On reaching the upper layers of the atmosphere they cool, condense and from cumulonimbus clouds. In the late afternoon the clouds burst into a heavy downpour, often accompanied by thunder and lighting. It usual occurs at about 4 pm, so convectional rain is called ‘four o’clock rain’ and occurs daily in the equatorial regions.Cyclonic Rain:In the mid latitudes warm moist air from the sub-tropics meets the cold polar air near the Arctic Circle. The plane along which they meet is called a front. The warm air being lighter rises up and condenses on reaching a certain height. Continued condensation causes heavy rain along the front. This rain is common at sub polar low pressure belts where the warm westerlies meet the cold Polar winds. The former rise up, cool and condense and give rainfall. Such rain is called frontal rainfall. In the tropics, winds blow in form all sides towards a lower pressure center. They move in a spiral motion at great speed. At the center, the air is forced to rise up. The sudden uplift of the warm air causes cooling and condensation and formation of cumulonimbus clouds which result in heavy rainfall. This rain is called Cyclonic rainfall.