Air is light but because there is so much of it above us, it exerts a pressure on us. Air pressure is measured by a barometer. The units used are millibars. The greater the reading, the higher the pressure.
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.
An area of low pressure is called a depression. Air rises in a depression so clouds and rainfall are formed. Depressions therefore bring unsettled weather and rain. Winds are normally stronger. They usually form over the Atlantic Ocean and are carried across Britain by westerly winds.
See the following video on anticyclone and depression.
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