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Winter High Pressure

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Snow falls in a forest at night.
High pressure brings difficulties during winter months. Fog, frost and even poor television pictures are some of the main problems. But why should this be?

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Winter anticyclones usually build westwards from Scandinavia and Eastern Europe. These areas are obviously extremely cold during the winter months and as they move westwards, the UK is often on the southern flank of the 'high'.

The wind-chill factor can be quite considerable.
With the winds tending to blow outwards in a clockwise direction, we often feel the force of an icy blast that originated from the frozen Steppes. The weather is often made to feel worse by the effect of a strong wind. The wind-chill factor can be quite considerable.

When the wind blows straight out of continental Europe it is often very dry with only small amounts of cloud. When this happens air temperatures can fall considerably. But when the wind is backed slightly towards the northwest the winds come over a longer stretch of the North Sea bringing more cloud. In this case frosts will be patchy as cloud acts as a blanket, helping to keep the night-time temperatures higher.

Fog can be very difficult to forecast in these situations....
Fog can be very difficult to forecast in these situations as it is highly dependent upon the presence of cloud, or lack of it. In this type of weather, forecasters spend their days chasing clumps of cloud on satellite pictures trying to work out if they will be sitting over their area at night.

High pressure can have other undesirable effects. With easterly winds often travelling across the industrial areas of Europe, the visibility can be quite poor. This type of weather was responsible for the 'pea-souper' fogs in London before the Clean Air Acts in the 1950s. Television pictures can be of variable quality as signals get trapped in the cold air.

Those with breathing difficulties often find that the cold, damp air can aggravate their problems. But after months of (seemingly) never-ending rain it is a relief to many of us to see the river levels falling and the fields becoming hard enough to walk on.

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Key Points

• Winter anticyclones can bring icy air from the frozen Steppes.
• Easterly winds in winter can bring poor visibility.
• Television pictures can be of variable quality as the signal becomes trapped in the cold air.

Air Pressure
High Pressure
Wind Chill
Wind Chill Effects