Steve Connor: Atlantic winds normally save us. Not this time

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The Independent Online

Britain's famously changeable maritime weather is dominated by the mainly westerly winds that come from the North Atlantic, whose water acts as a moderating influence over the extremes of summer heat and winter cold.

However, a large area of high pressure has developed over the Atlantic which acts as a "block" against these relatively mild westerlies. As a result, bitterly cold Arctic air has moved south over much of north-western Europe.

Mainland Europe at this time of the year gets very cold at night because land loses heat so much more quickly than the sea. North-easterly winds have brought this cold air mass over Britain, but in doing so it has to cross the relatively warmer North Sea, picking up moisture in the process and then dumping it as snow showers over Scotland and eastern England.

Ewen McCallum, chief meteorologist at the Met Office, said that the localised nature of these snow showers means that some areas, for example just north of London, have remained relatively free of deep snow, while other areas to the south of the capital have been badly hit.

Some areas in the Scottish borders have seen up to 44cm (17in) of snow, while at Kielder Castle in Northumberland, locals have had to cope with 40cm. Temperatures too have plummeted, with Altnaharra in Scotland falling as low as minus 21.1C

"Because the air is so cold, this has resulted in snow showers and with the wind coming from the east, it is coastal areas along the North Sea that have seen the heaviest snow. The localised nature of showers means that the amount of lying snow has varied greatly from place to place," Mr McCallum said.

"It is very unusual for a period of easterly winds to bring such heavy and prolonged snowfall. In fact for November, the amounts this year have been the most widespread in the UK since 1993, and the deepest November snow since 1965," he said.

"One reason why we have seen such large amounts of snow is that the [atmospheric] pressure is much lower than normal, allowing the air to rise and form deeper clouds, therefore producing heavier showers," he added.

Although the winter weather appears to have come earlier this year, scientists believe that the phenomenon is still within the range of natural variability and says little about the longer global influence of climate change.

Last year, while Britain experienced one of its coldest winters on record, western Canada had a relatively mild winter. At the same time, the southern hemisphere had its warmest year on record – underlying the regional variability of the weather.