Headline : Average to slightly above average temperatures. Drier than average.

Forecast Methodology

For the 2005/6 Winter forecast, Metcheck have used a mixture of the correlation between mid-summer snow cover across the Eurasian Plateau (Qian et Saunders) and the effect of an above average hurricane season.

This data, along with model output from the CFS (Coupled Forecast System) from NOAA have been used to provide a forecast from December 2005 to February 2006.

Eurasian Plateau Snow Cover

Recent studies show that snow cover across the Eurasian Plateau during the preceding years early summer, show a strong correlation with the forthcoming winters weather across Europe. Feedback skills show that by using this method, the accuracy of forecasts for Atlantic activity in the forms of gale force winds can be increased to 69% as opposed to 36% by simply assuming that this winter will always be stormy.

The theory, is that if the period from June-August shows above average snow cover, then the forthcoming winter will be less stormy and in return, more settled and generally colder than average.

Using data from Rutgers Snow Lab, we can deduce that the average snow cover across the Eurasian Plateau from June to August is 2,207,000km² since records began in 1967. This year, the average was 1,355,000km².

This indicates that with a lower than average Eurasian Plateau snow cover that this winter will see more stormy days than we would usually expect.



The image above shows the snow cover anomaly for the June-August period in '000s km² since 1967.

The effect of above average Eurasian Plateau snow cover is known to affect the surface temperatures coming off the Plateau and across the Pacific ocean. This temperature difference can produce circulation changes which affect summer snow cover across the Canadian Northwest territories and sea surface temperature anomalies across the Barents Sea and Atlantic Ocean.

Coupled with these sea surface temperature changes, this then in turn feeds back into the atmosphere.

Hurricane Season
The 2005 hurricane season has been phenomenal in many respects. The highest number of named storms, the lowest recorded pressure in the Atlantic Basin and the highest number of named hurricanes.

A weak statistical link is known between the activity of the preceding hurricane season and the forthcoming winter. The higher the activity, the higher the chance of a colder than average winter. This has been taken into account for the final forecast.

Coupled Forecast System
The new CFS (Coupled Forecast System) from NOAA is a model based on land/sea interactions over the coming six months. The reason for coupling is that there is a strong relationship between how areas of high pressure interact with regions of unusually warm or cold sea surfaces.

This forecast, along with others from leading global agencies is indicating a colder than average winter for much of Europe, however is reluctant to bring the cold weather as far West as the British Isles.

The reason for this is that the model is confident of high pressure building across the North and to the West of the British Isles during the winter period.

This scenario would force the polar jet stream further South than average in the longer term and would indicate a bias towards a negative NAO this winter.

A negative NAO however, doesn't always indicate a colder than average winter. If low pressure is forced further South, then approaches the UK from the South-west, then this will introduce milder air across the country than usual.

2005/6 Forecast
The overall indication for this coming winter is for temperatures to be average to slightly above average for the season (December-February). However, the consistent forecast for Europe to be colder than average indicates that any Easterlies which do occur this year will be markedly colder than seen during recent winters.

Temperature Forecast (against 1967-2004 averages)
December : Average/Slightly below
January : Average/Slightly above
February : Average/Slightly above

Precipitation Forecast (against 1967-2004 averages)
December : Below
January : Slightly below
February : Slightly above

Conclusions
The Winter of 2005/6 across the British Isles is expected to rank alongside the one of 2004/5 with the same expected level of frequency of cold weather incursions. However, these spells are expected to be colder than those of last year.

The winter as a whole is unlikely to deviate significantly from average values, however with the UK becoming accustomed to traditionally milder winters in recent years, this winter is likely to appear colder than normal, however we are expecting final figures to show values at or slightly above average.

A feature which will be monitored is developments of anticyclones to the North and West of the UK. The day-to-day fluctuation of this feature has the potential to bring colder outbreaks in from the North and North-east. This, we feel, is the feature which could affect the forecast during the period and as a result confidence levels in the winter forecast are as follows :-

Significantly colder than average : 5%
Slightly colder than average : 20%
Average : 30%
Slightly warmer than average : 40%
Significantly warmer than average : 5%

Forecast Issued : November 2nd 2005
Forecasters : Bond/Hugo

This forecast will be verified in full at the end of the forecast period : March 1st 2006

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