Anticyclones in the British Isles

A high-pressure system is called an anticyclone.

Air falls in an anticyclone so no clouds are formed.

In summer, high pressure usually results in clear skies, gentle breezes and fine weather.

In winter, high pressure leads to clear skies and colder conditions.

Map showing path of a typical anticycloneSynoptic chart of a typical summer anticyclone

Key features of a summer anticyclone

  • Pressure – High and increasing (over 1000 mb)
  • Temperature – Very warm air will be brought over from continental Europe. This will bring hot, sunny days and ‘heatwave’ conditions.
  • Cloud cover – Sinking air means that air is settled and clouds will not be formed. Temperatures at night will drop as heat will escape back into the atmosphere.
  • Wind speed and directionIsobars are not close together, there is very little wind and conditions will be calm. Any wind will rotate in a clockwise direction.
  • Precipitation – Very little precipitation but there can be mist and fog early in the morning, though this is usually burned off by the sun very quickly.

Key features of a winter anticyclone

  • Pressure – High and increasing (over 1000 mb)
  • Temperature – Temperatures are much lower. The sun is low in the sky so there is less heating in the air.
  • Cloud cover – Sinking air means that air is settled and clouds will not be formed. Temperatures at night will drop very quickly as heat will escape back into the atmosphere. This can cause freezing conditions – frost, fog and ice.
  • Wind speed and direction – Isobars are not close together, there is very little wind and conditions will be calm. Any wind will rotate in a clockwise direction.
  • Precipitation – Very little precipitation but there can be mist and fog early in the morning and sometimes a temperature inversion near ground level will cause heavy fog and frosty conditions.