Weather

Temperature

Because of the North Atlantic Drift and the predominantly maritime air masses that effect the British Isles, the range in temperature throughout the year is never very great. The annual mean temperature in England and Wales is about 10°C, in Scotland and Northern Ireland about 9°C. The mean January temperature for London is 4°C, and the mean July temperature 17°C.

Near sea level in the west the mean annual temperature ranges from 8°C in the Hebrides to 11°C in the extreme south-west of England. July and August are the warmest months of the year on average and January and February the coldest. The mean summer temperatures throughout Britain increase from north to south.

The mean monthly temperature in the extreme north (the Shetlands) ranges from 3°C during the winter (December, January and February) to I2°C during the summer (June, July and August). The corresponding figures for the Isle of Wight, in the extreme south, are 5°C and I6⁰C.

During a normal summer the temperature may occasionally riseabove 30°Cin the south. The highestshade temperatureeverrecorded in Britainwas about 37°Cin August 1911 in Northampton-shire, Surrey and Kent. Minimum temperature of - 10°C may occur on a still, clear winter's night in inland arear. Lower tempera­tures are rare. The lowest temperature (-27.2°C) wasrecorded at Braemar (the Grampians) in February 1895 and January 1982.

The distribution of sunshine shows a general decrease from south to north, a decrease from the coast inland and a decrease with latitude. During the months of longest daylight (May, June and July) the mean daily duration of sunshine varies from five hours in northern Scotland to eight hours in the Isle of Wight. During November, December and January (the months of shortest daylight) sunshine is at minimum, with an average of half an hour a day in some parts of the Scottish Highlands and two hours a day on the south coast of England. Generally the coasts are everywhere sunnier than neighbouring inland districts. Ireland is subject to frequent cloud and records little sunshine.

In direct contrast with climate, in which short-term variations disappear with the calculation of averages, the weather of the British Isles is notoriously variable. Not only is it liable to day-to-day changes- some whole seasons are markedly wet, markedly dry, unusually cold, or unusually warm.

Spring is normally Britain's driest season, even though April is by tradition showery. Cold weather usually lasts no later than mid-April, and there are frequently some very warm days during the second half of the month. By late spring daytime temperature rises considerably, and the thermometer may even reach 2I-24°C over a wide area.

June is the brightest month of the year for Britain in general. Rainfall tends to increase during July and August, partly because Atlantic depressions some nearer to the coast during these months and partly also because air, as it becomes warmed, is capable of holding more moisture. Late summer is often noted for vary warm weather, and this way continue into September.

North and north-west winds often bring heavy falls of snow to north Britain during late October and November, but they are usually short-lived.

Continental air sometimes reaches the British Isles in summer as a warm, dry air-stream, but it is more frequently experienced in winter when it crosses the North Sea and brings bitter weather to eastern and inland districts of Great Britain.

In fine, still weather there is occasionally haze in summer and mist and fog in winter.

Дата добавления: 2014-01-05