Seeing the future: Met Office unveils new winter forecasts

The next generation prediction system offers the potential to give more useful guidance on winter weather patterns up to weeks ahead.

A combination of increased computer power and better modelling have created the highest resolution operational long range forecast system in the world – something that is the result of years of development work by Met Office scientists.

The size of the grid boxes which the model uses to work out the forecast have shrunk to 25km over the oceans and 50km in the atmosphere.

Smaller grid boxes enable the model to observe and predict what will happen more closely, which allows for a better forecast.

One key development from this new long-range forecasting system is better modelling of the North Atlantic Oscillation (NAO), which is a measure of the difference in air pressure between Iceland and the Azores.

When the NAO is positive, this pressure difference is high, implying a stronger jet stream and wetter, milder winter weather.

However, when the NAO is negative, this pressure difference is low, suggesting a weaker jet stream and colder, drier winter weather.

Better predictions of the NAO will enable improvements in risk based forecasts and potential impacts on energy supply, transport infrastructure, flooding, and storm damage.

Professor Adam Scaife, Head of Monthly to Decadal Prediction at the Met Office, said: “This is not a silver bullet for providing forecasts of weather on individual days months ahead, but it is an important step forward in our efforts to better predict the risk of disruptive winter weather weeks ahead.”

He added: “As with any long-range forecast, the new system delivers forecasts of the risk of different types of winter conditions. There is still a lot to do in this challenging area of science and we will always see occasions where winter weather does not match the most likely forecast scenario. Nevertheless this is a major step forward and underlines our confidence that further research can deliver even greater benefits.”

Testing of the system has been carried out by looking at 20 past winters, including the extreme winters of 2009/10 and 2010/11, as well as the mild stormy winter of 2011/12.

For each winter, the forecast system was run from early November through to March, using only observations that would have been available at the time of the start of the forecast.

In total, 24 different forecasts (known as an ensemble) are produced for each winter, which then allows an assessment of the risks of certain types of winter weather to be made.

It is hoped that further technological advances in the future will allow the accuracy rate to improve even more.