Climate and Weather in Great Britain
Weather is not the same as climate. The weather at a place is the state
of the atmosphere there at a given time or over a short period. The
weather of the British Isles is greatly variable.
The climate of a place or region, on the other hand, represents the
average weather conditions over a long period of time.
The climate of any place results from the interaction of a number of
determining factors, of which the most important are latitude, distance
from the sea, relief and the direction of the prevailing winds.
The geographical position of the British Isles within latitudes 50o to
60o N is a basic factor in determining the main characteristics of the
climate. Temperature, the most important climatic element, depends not
only on the angle at which the sun’s rays strike the earth’s surface,
but also on the duration of daylight. The length of day at London ranges
from 16 hours 35 minutes on June to 7 hours 50 minutes on 21 December.
British latitudes form the temperate nature of the British climate, for
the sun is never directly overhead as in the tropical areas.
Britain’s climate is dominated by the influence of the sea. It is much
milder than that in any other country in the same latitudes. This is due
partly to the presence of the North Atlantic Drift, or the Gulf Stream,
and partly to the fact that north-west Europe lies in a predominantly
westerly wind-belt. This means that marine influences warm the land in
winter and cool in summer. This moderating effect of the sea is in fact,
the cause of the relatively small seasonal contrasts experienced in
The moderating effect of the ocean on air temperature is also stronger
in winter than in summer. When the surface water is cooler than the air
above it – as frequently happens during the summer months – the air
tends to lose its heat to the water. The lowest layers of air are
chilled and become denser by contradiction, and the chilled air tends to
remain at low levels. The surface water expands because it is warmed,
and remains on the surface of the ocean. Unless the air is turbulent,
little of it can be cooled, for little heat is exchanged.
Opposite conditions apply in winter. The air in winter is likely to be
cooler than the surface water, so that the heat passes from water to
air. Air at low levels is warmed and expands and rises, carrying oceanic
heat with it, while the chilled surface water contracts and sinks, to be
replaced by unchilled water from below. This convectional overturning
both of water and of air leads to a vigorous exchange of heat.
The prevailing winds in the British Isles are westerlies. They are
extremely moist, as a result of their long passage over warm waters of
the North Atlantic. On their arrival to Britain, the winds are forced
upwards, and as a result large-scale condensation takes place, clouds
form and precipitation follows, especially over the mountainous areas.
North and north-west winds often bring heavy falls of snow to north
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