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FACTBOX-The NAO forecast to bring Europe a colder winter

Source: Thomson Reuters Foundation - Fri, 28 Oct 2011 15:08 GMT
Author: Reuters
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LONDON/FRANKFURT Oct 28 (Reuters) - Britain and western Europe are expected to see below average temperatures this winter as the North Atlantic Oscillation (NAO) continues to dominate countries with exposure to the Atlantic Ocean, weather specialists said.

The NAO is the dominant mode of winter climate variability in the North Atlantic region, which ranges from central North America to Europe.

The NAO is considered positive when pressures and heights are below normal over Greenland and Iceland (strong Icelandic low) and above normal at middle and subtropical latitudes (strong Bermuda-Azores high) -- and negative for the reverse anomalies.

The NAO has largely been negative during the past three winter seasons, causing cold and wet winters along Europe's Atlantic and North Sea coasts and wetter, windier weather across the Iberian Peninsula and Italy as westerly winds from the Atlantic are pushed South.

Most meteorologists expect it to dip again this winter.

The NAO has been positive in September and October, but it has begun to dip in recent days and has entered negative territory, according to data from the US National Weather Service.

Below is a summary of European seasonal weather forecasts:

POINT CARBON

Point Carbon, a sister company of Thomson Reuters, said it expected the first parts of the coming winter to be cooler than average.

Later on in winter, the weather is likely to be changeable, with a possibility of milder than average weather.

"The second half of November and the first half of December could be cooler than normal," said Point Carbon's Georg Mueller.

From January onwards, the weather could be more unsettled, wetter and milder than normal especially in northern Europe, while central Europe could trend towards a high pressure influence and calmer weather, according to Point Carbon.

WORLD CLIMATE SERVICE (WCS)

WCS said it expected the coming winter to be dominated by a negative phase of the NAO, resulting in colder, dryer, and less windy than average weather on the British Isles, in France, Germany, and the Nordic and Baltic countries.

Mediterranean countries should expect a mild, windy and wet winter.

"We expect another winter of unusual cold and occasionally disruptive snow from the British Isles and France across Germany and southern Scandinavia to the Baltic states," Richard James, senior meteorologist at WCS said.

"The highest likelihood of unusual cold appears to be in early to mid-winter (late November to January), with moderating conditions possible by February. Wet conditions will prevail in southern and southeastern Europe, but it will be generally dry in the north."

WCS also said that said that the negative NAO was likely to be a phenomenon that would dominate Europe's winters for years to come.

"There are definitely decadal trends, and there is a chance that there could be a long negative NAO phase," James said, and added: "the last time we saw such a phase was in the 1950s and '60s", which was a period that dominated by cold winters in Europe.

WEATHER SERVICES INTERNATIONAL (WSI)

WSI, which specialises in weather information for use in the energy sector, said it expected temperatures until December to be below average in the UK and western European mainland, while the eastern mainland, Southeast Europe and most of the Nordic region will be warmer than average.

"The high-latitude atmospheric blocking regime, as manifested by the negative phase of the NAO, is expected to dominate the pattern again across Europe during late autumn and early winter," said WSI Chief Meteorologist Todd Crawford.

However, Crawford also said that he did not expect this winter to be as cold as the previous two.

"We don't expect a very cold winter this year," he said, adding that it could be more like the winter of 2008/2009, which brought below-average temperatures but was slightly warmer than the following two winters.

THE WEATHER OUTLOOK (TWO)

TWO said it expected autumn 2011 weather conditions in Britain to be mixed and at times stormy but possibly with "a wintry sting" during November.

Until the end of November, "temperatures are forecast to be close to average, although with a slight bias towards colder than average conditions," TWO said.

TWO also said it expected overall autumn precipitation amounts to be close to or slightly above the average, although it also said that significant regional variations were expected across Britain.

EXACTA WEATHER

Exacta weather said it expected November, December, January, and February to feature largely below-average temperatures across many parts of the UK.

"I expect the most frequent and heavy snowfalls to occur across many parts of the UK during November, December, and January," Exacta Weather's James Madden said.

POSITIVE WEATHER SOLUTIONS (PWS)

PWS said it expected November for most UK regions to be slightly drier than the norm and temperatures to approach average in the south-east, but turn out milder across some western and northern regions.

For the continental European regions of France, Germany and Switzerland, PWS said it expected temperatures to be cooler than average between October 2011 and February 2012.

"The last month of autumn looks rather variable, with dry and damper influences each trying to predominate," PWS's Ray Anthony said. (Compiled by Henning Gloystein and Philip Baillie in London, and Vera Eckert in Frankfurt, editing by Jane Baird)

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