Weathermen: We can predict big freeze a year ahead

IT has made heavy weather of its predictions in the past – failing to warn us about the Big Freeze of 2009.

But the Met Office says it can now forecast our winter weather a year in advance after unlocking the mysteries of a weather system that controls our climate.

British winters are notoriously unpredictable, driven by chaotic meteorological processes that follow few patterns. Met Office scientists had thought it impossible to forecast the phases of the North Atlantic Oscillation (NAO), which drives the winter weather in Europe and North America.

But they now believe they can forecast the phenomenon caused by the pattern of high and low pressure above Iceland and the Azores, an archipelago in the North Atlantic west of Portugal.

The NAO goes through two phases, with a large pressure difference between Iceland and the Azores bringing mild, stormy and wet winter conditions to the UK.

A smaller difference in pressure usually means a big freeze – like the one of 2009-10 that caused transport chaos in Britain and was blamed for 90 deaths in Europe.

The Met Office used its £100million supercomputer, which weighs as much as 11 double decker buses and performs 16,000 trillion calculations a second, to look back at previous winters and make ‘hindcasts’ in what is described as back-testing.

Using weather data going back 35 years, they discovered they could predict what the weather was going to do each time with 62 per cent accuracy.

The results have been published in journal Nature Geoscience and the Met Office’s lead author Dr Nick Dunstone said they showed a ‘modest but significant skill’ in predicting the phase of the NAO one year ahead.

‘This is an exciting first step in developing useful winter climate predictions on longer timescales,’ he said. ‘Understanding and predicting the changes in the North Atlantic Oscillation could have significant economic benefits, including potential boosts in climate services for a range of sectors including transport, energy, water management and the insurance industry.’

More advanced forecasts could mean better weather warnings for sub-zero temperatures and winter storms. This would be a lifeline for transport firms, or local authorities planning how much grit to buy.

Using its new computer capacity last year, the Met Office was able to advise people of the flooding threatening coastal communities. For the coming winter, forecasters are predicting a cooler and drier season.