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Anticyclones in the UK

Learn more about anticyclones in the UK

In the UK and much of western Europe, high pressure dominated through the spring of 2020, giving us clear skies and record breaking sunshine hours, giving way to some more unsettled weather in early June which saw some convective storms with lightning, waterspouts etc, develop across the Mediterranean and eastern Europe. This Met Office video on YouTube has some great graphics which relate to the processes which we’ve been considering in Come Rain or Shine.

In July 2022, High pressure conditions led to:

• Some parts of the UK saw temperatures reach over 40°C for the first time in recorded history.

• Highest temperature recorded was 40.3°C in Coningsby, Lincolnshire.

• Temperatures were between 2 – 4°C warmer than they would have been without global warming.

• National Emergency declared.

• Almost 25,000 wildfires across the country.

• The London fire brigade had its busiest day since WW2.

• Over 4,500 deaths.

When anticyclones are over the sea, the weather can vary from fine and sunny to overcast cloud. This cloud may be thick enough to give drizzle and may form low enough to produce fog. This happens most often during spring and is least frequent in autumn. If the anticyclone extends over both land and sea, cloud and fog can spread across coastal regions, sometimes reaching quite far inland.

Sometimes, an anticyclone doesn’t move and remains stationary over the UK or nearby for a longer period of time. These ‘Blocking Highs’ divert the much smaller depressions away and lead to a longer period of clear weather, as can be seen in Figure 1.

Figure 1: A schematic diagram showing how the wind fields around a large anticyclone and small depression interact
During the summer, these blocking anticyclones can lead to drought conditions, as rain-bearing fronts are ‘diverted’ around the country. This is what happened in 1976 when an anticyclone sat over the UK for much of the summer, causing a noticeable drop in rainfall, well below the normal average, and leading to water shortages.
The summer of 2013 was dominated by anticyclones (Figure 2), leading to prolonged nice weather in England and Wales. In the satellite image in Figure 3 you can see a line of cloud to the North of Ireland. This marks the warm front associated with the Low near Iceland which you can see in the weather chart. This Low will travel to the north of the UK, bringing rain to Norway.
Figure 3: A typical satellite image from July 2013 ©NEODAAS/University of Dundee
Spring 2013 was also characterised by high pressure – the weather chart (Figure 4) shows a typical situation with high pressure over all of the UK. The high pressure blocked milder, Atlantic air from reaching the UK as well as bringing bitterly cold, north-easterly/ easterly wind. Remember that winds blow around anticyclones in a clockwise direction along the isobars, and see what that means the wind direction is.

Occasionally, the High moved to allow depressions to move up the west coast of the UK – where the rain on the fronts met the very cold air to the east, it resulted in heavy snowfall. The generally clear night-time skies at a time of year when the Sun wasn’t warm enough during the day to warm the ground much, led to the second coldest March since 1910. The winter snow persisted far longer than usual, leading to problems for hill farmers with sheep lambing into the snow (Figure 5). In parts of Wales laws were relaxed concerning the burial of dead livestock.

Figure 5: “Sheep in a field near Pwllglas” by Eirian Evans via Wikimedia Commons, CC BY-SA 2.0

Summary

Anticyclones:

  • are larger than low pressure systems
  • last longer than low pressure systems
  • have lighter winds blowing around them
  • have clockwise winds blowing around them in the Northern Hemisphere
  • usually give us clear skies
  • can give us ‘Anticyclonic gloom’ in spring.
© University of Reading and Royal Meteorological Society
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Come Rain or Shine: Understanding the Weather

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