UK Weather

What causes the weather in the UK?

The two major atmospheric characteristics that are the reason for the majority of the weather in the UK are depressions and anticyclones.

A depression is an area of low pressure. Air rises leading to the formation of clouds and rain. UK weather is associated with the movement of depressions across the land. Depressions form over the Atlantic Ocean and pass from West to East across the UK driven by the prevailing winds. Depressions form at the boundary between cold polar air moving South and warm tropical air moving North and is known as the polar front. Once formed, the air begins to rotate, spiralling upwards in an anti-clockwise direction forming clouds and then rain.

Within a depression there are two further ‘fronts’, one cold and one warm. The warm front signifies the front of the warmer air (hence the name, genius!) and the cold front........you get the idea. As the depression builds it eventually dies out as the cold front catches up with the slower warm front. As depressions pass over the UK a sequence of weather is produced. At the front of the depression a steady rain falls. Behind this, small patches of rain begin to fall as the temperature rises slowly due to the warm air. The advancing cold front causes the temperature to drop and the rain ceases.

Unlike depressions, anticyclones are areas of high pressure cause by descending air. The chances of rain are slim as the descending air prevents air from rising and therefore forming clouds. Winds also travel clockwise, the opposite of depressions. Anticyclones can be separated further into two main types, winter and summer anticyclones. In winter, cloudless skies result in bright but cold conditions. As there is no cloud heat it lost rapidly into the atmosphere and this is what causes frost to appear on the ground in the early morning. If the air is particularly heavy with moisture from the surrounding seas then can condense into mist and fog. In the summer time the sun is much stronger due to Earths’ rotation on its axis and is easily able to burn away and resulting mist and fog. Summer anticyclones typically result in dry, sunny conditions (of which we see very little these days). The below diagram is a basic example of an anticyclone situated over the UK.