Extreme weather in the UK Flashcards
What causes UK weather?
Two different pressure systems bring different types of weather to the UK. They are depressions and anticyclones.
Whats a depression?
A depression is an area that has low atmospheric pressure. Air rising causes the formation of clouds, which brings rainfall. Depressions often move eastwards across the UK, bringing changeable weather as they travel.
There are usually frontal systems associated with depressions. The diagram below shows the changing weather that the warm and cold fronts bring as they move towards the east.
What are anticyclones?
Anticyclones are areas of high pressure which form when cool air sinks. Anticyclones spin around in a clockwise direction. Anticyclones make skies clear and cause different weather in summer and winter. In summer, anticyclones bring hot, sunny weather. During winter, anticyclones cause cold weather including fog and frost.
Whats rainfall like in the UK?
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 southwest prevailing winds bring moisture from the Atlantic Ocean.
What are the 3 different types of rainfall?
relief
convectional
frontal
Whats the process of relief rainfall?
Relief rainfall occurs when warm, moist air from the Atlantic Ocean rises up over mountains.
When the warm air rises, it cools and condenses to form clouds, which brings rain.
Once the air has passed over the mountains, it descends and warms.
This creates drier conditions known as a rain shadow.
Whats the process of convectional rainfall?
Convectional rainfall usually occurs during the summer in the UK, when the sun heats the land.
This creates rising pockets of warm air, known as convection currents.
Warm air rises rapidly, where it starts to cool and condenses to form clouds.
These clouds can be large cumulonimbus clouds.
The clouds can produce heavy rainfall and thunderstorms.
Whats the process of frontal rainfall?
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.
When the warm air rises, it cools.
The cooler air condenses and form clouds.
The clouds bring heavy rain.
What are examples of extreme weather?
The UK's weather is becoming more extreme. Some examples of extreme weather in the UK include: heavy rain gales floods heavy snowfall thick fog heat wave drought
How is climate change linked with extreme weather?
Climate change can increase the frequency and intensity of extreme weather events.
Flooding is becoming more frequent in the UK. The Environment Agency is responsible for monitoring the potential for flooding. They evaluate the risk of flooding and issue warnings for areas. They use three codes to help people be able to prepare: what are they?
Flood alert – Flooding is possible. Be alert.
Flood warning – Flooding is expected. Immediate action required.
Severe flood warning – Severe flooding. Danger to life.
Whats a rain shadow?
An area with reduced rainfall because it is behind higher land.
