High Pressure Weather: Anticyclones

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High Pressure Weather Anticyclones
CW
1st February 2006

• Lesson Aims
• To plot a typical Anticyclone
• To understand the weather associated with High
  Pressure

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Introduction

• Anticyclones are areas of high pressure. They
  affect the British Isles far less often than
  depressions. However, once in position, an
  anticyclone may stay for several days. They
  usually bring fine weather and are most common in
  summer

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How do anticyclones form?

• Anticyclones form in places where the air is
  descending. As more and more air descends, so the
  pressure increases and an area of high pressure
  develops.
• When the air descends it also warms up and is
  able to pick up moisture. This usually results in
  settled conditions with clear skies and little
  chance of rain.
• Sometimes, if the ground is cold. Low cloud and
  fog may form when the moist air comes in to
  contact with the cold surface. This happens most
  often in winter, or on a summers morning after a
  cloudless night

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• In many respects, anticyclones are the opposite
  to depressions. They are high pressure systems,
  they move slowly and usually produce settled
  weather. They are also caused by descending air.
  This means that clouds are unlikely to develop
  and the weather is usually dry and sunny

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Anticyclones in Summer-

• Very little cloud
• Dry with light wind
• Sun high in the sky, so hot and sunny
• Cloudless skies at night allow heat to escape, so
  nights can be cool
• Early morning dew and mist
• Risk of thunderstorms at end of heatwave
  conditions

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Anticyclones in Winter-

• Dry and bright with very little cloud
• Sun low in the sky, so cold conditions
• Clear evening skies mean that nights can be very
  cold
• Early morning frost and fog may last all day
• Extensive low cloud or fog may produce overcast
  or gloomy conditions

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Task

• Page 83 Key Geography
• Activities 1 2

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Conclusion

• 3 things Ive learnt today