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Rainfall

On average, it rains one in three days in the UK. Highland areas to the west receive the most annual rainfall compared to the low-lying areas in the east. The south-west prevailing winds bring moisture from the Atlantic Ocean.

Types of rainfall

There are three different types of rainfall:

• relief
• convectional
• frontal

Relief rainfall

1. Relief rainfall occurs when warm moist air from the Atlantic Ocean rises up over mountains.
2. When the warm air rises, it cools and condenses to form clouds, which bring rain.
3. Once the air has passed over the mountains, it descends and warms.
4. This creates drier conditions known as a rain shadow.

Convectional rainfall

1. Convectional rainfall usually occurs during the summer in the UK, when the sun heats the land.
2. This creates rising pockets of warm air, known as convection currents.
3. Warm air rises rapidly, where it starts to cool and condenses to form clouds.
4. These clouds can be large cumulonimbus clouds.
5. The clouds can produce heavy rainfall and thunderstorms.

Frontal rainfall

1. Frontal rainfall occurs when a warm front meets a cold front. The heavier cold air sinks to the ground and the warm air rises above it.
2. When the warm air rises, it cools.
3. The cooler air condenses and form clouds.
4. The clouds bring heavy rain.