High and low pressure: How do they affect the weather in the UK?

By Charlotte Smith

22 January 2018

Trinity Mirror

After days of severe snow and ice and bitter northwesterly air, unsettled, wet and windy weather is on the way as high and low pressure battle it out.

Ever-changing weather conditions in the UK are normal for January, with days of plunging temperatures and wintry spells quickly followed by strong wind and heavy rain.

Humid, muggy and damp weather is forecast dominate the early part of this week as mild, tropical air from the Azores moves across the country - forcing temperatures to edge upwards.

However, the despite the warm boost, potent low pressure systems from the Atlantic will bring downpours with risk of gales by Wednesday. 

The reason why the UK faces such radical changes is down to the planet’s air pressure system.

The Earth’s atmosphere exerts a pressure onto the surface which influences the movement of air around our planet.

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Air pressure is divided into two types that are known as high pressure and low pressure.

This is what brings such changes to British weather on a daily basis; turning what could be a one day of rain and snow into one of mild sunny spells the next.

In general, areas of low pressure develop clouds and precipitation that lead to unsettled conditions. While areas of high pressure tend to bring clear, bright and more settled weather conditions.


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As air warms, it rises and leads to low pressure on the surface. And as air cools, it falls resulting in high pressure on the surface.

Hannah Findley, forecaster of The Weather Channel, says the location of areas of high and low pressure affect the wind direction, which has an impact on temperatures.

In an anticyclone, otherwise known as a high pressure system, the wind is usually light and blows in a clockwise direction - in the northern hemisphere.

During this, the air is also descending, resulting in clear skies and dry and bright conditions.

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While in a depression, also known as low air pressure, air ascends and travels in an anticlockwise movement around the low air.

Throughout this motion of rising and cooling, water vapour condenses to form clouds and rain.

Hannah Findley, adds: "High pressure means that air is sinking in a certain area. It leads to settled conditions, usually with very little cloud and precipitation and light winds.

"Clear skies generally leads to much warmer temperatures in summer and during the daytime because it lets the sun's radiation reach and heat the ground.

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"However, a lack of cloud cover also allows radiation to leave the earth easily so leads to cold conditions in winter and at night.

"Under high pressure temperatures generally vary quite widely between day and night - this is called the diurnal range."

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