Weather PORTAL
The climate of Britain
Britain is in the temperate climate zone and does not have extremes of temperature or rainfall. The Gulf Stream, a large Atlantic Ocean current of warm water from the Gulf of Mexico, keeps winters quite mild whilst during summertime, warm but not excessively hot temperatures are experienced. The average annual temperature in Britain is about 10C, with the summer average temperature being around 15C and the winter average being around 5C (day and night). As we have seen in previous sections, the British weather is dominated by frontal depressions which form in the Mid-Atlantic and pass across into Europe, bringing changeable weather.
The main air masses that affect Britain are those that form over the Mid-Atlantic but there are several other air masses that bring particular weather conditions. The air masses are defined according to where they originated and their course of travel. For example air from Arctic regions is classified as Arctic maritime as it originates in the Arctic and travels across the North Sea. Another example is Tropical maritime air which originates near the Gulf of Mexico and travels across the warm Atlantic Ocean before arriving in Britain. Other air masses include the Polar maritime, Polar continental and Tropical continental. Examples of air masses which affect British weather are shown on the diagram below.
Most of the airflow across Britain throughout a year is maritime, including tropical and polar air masses. Tropical maritime air is mild in winter and warm and humid in summer. If these air masses are associated with frontal depressions, there is usually plenty or rainfall, but when associated with anticyclones, settled weather with warm sunny spells occurs.
Polar maritime air masses usually result in cool, showery weather throughout the seasons but may bring snow during the winter months.
Polar continental air in winter is very cold. The air mass is usually dry and stable but as it passes over part of the North Sea, sufficient heat and moisture can lead to the formation of showers, often snow, over eastern England and Scotland. During summer, the polar air mass brings warm air as even northern parts of Europe experience high temperatures during the summer months.
Tropical continental air reaches Britain from the Saharan region of Africa. It gives dry weather in the summer and also gives pleasantly warm weather in the winter.
The general patterns of climate experienced in Britain have been identified. However, there are also noticeable differences that occur throughout Britain. The coldest winter temperatures in Britain occur in eastern Scotland and England. The western side of Britain is warmed by the influence of the tropical maritime airstream. Temperatures are therefore colder in the east than in the west during winter. During summer the south is warmer than the north. This is due to the differences in solar heat received, being greater in the south.
The British climate can be divided into four parts as shown on the map below. The northwest section is characterised by mild winters and cool summers and the northeast with cold winters and cool summers. The southwest experiences mild winters and warm summers and the southeast with cold winters and warm summers. Western parts of Britain generally experience a more maritime climate during winter whilst eastern Britain is influenced by the cold airstreams from the European continent. In summer, climate differences are more dominated by latitude.
Precipitation also varies throughout Britain. Western Britain, particularly the parts on higher ground, receives considerable rainfall. Most of this is frontal rainfall but there is also relief rainfall due to the mountains such as the Lake District and the Welsh Mountains. Parts of Scotland can receive over 250 cm or 100 inches of precipitation per year. Eastern Britain, particularly southeastern parts, receive much less rainfall. Areas of the southeast may receive only 50 cm or 20 inches of precipitation per year. Much of eastern Britain lies in the rain shadow of hills and mountains such as the Lake District, the Peak District and the Scottish Highlands.