Damaging winds from European cyclones

Professor Keith Browning.
University of Reading.

Peter Clark and Tim Hewson.
Met Office.

Dr Robert Muir-Wood.
Risk Management Solutions.

Strong winds during severe storms cause over one billion Euros of damage in Europe in an average year. By piecing together events during European cyclones, including the Great Storm that swept over southeast England in October 1987, meteorologists have found that the most damaging winds are concentrated in a small region known as a Sting Jet. Armed with an understanding of this new weather phenomenon, forecasters are now better able to predict where the worst winds will strike, hopefully reducing loss of life.

Extra-tropical cyclones lash Europe in winter with surface winds that can gust at 80-100 mph. Over Christmas 1999, two storms in France caused 3.4 billion Euros of forestry losses, left 3.5 million people without electricity and one million without telephone lines.  If a similar storm had crossed London, it would probably have killed up to 300 people, depending on the time of day.

Other examples include the Burns' Day Storm of 1990 and the 1997 Christmas Eve storm. The total insured loss from this type of storm in Europe is estimated to have been 24 billion Euros between 1985 and 2001. Although such storms are more common in winter, they can occur in summer - one coincided with the Fastnet yacht race on 14 August 1979, during which there were several fatalities.

But predicting the strong winds associated with these storms is difficult, as weather forecasters famously found out during the Great Storm of October 1987. Even within 2 hours of the 1999 French storms, forecasts were underestimating wind speeds by 25% - equivalent to a 6 to 8-fold underestimate of the amount of damage that they caused.

To understand the conditions that lead to such strong winds, Professor Keith Browning of the University of Reading and his colleagues have carried out a detailed analysis of the Great Storm of October 1987. Looking at satellite images of clouds and surface weather observations, the researchers have pieced together in some detail the conditions that lead to the strongest surface winds. A stream of strong winds descends to the ground where there is evaporation at the tip of a tell-tale cloud feature. This cloud, hooked like a scorpion's tail, gives the wind region its name - the Sting Jet.

The researchers tested their ideas in a new high-resolution numerical weather forecasting model developed by the Met Office, which was able to recreate the Sting Jet effect. Knowing how the Sting Jet behaves should allow forecasters to look at satellite images of storms and predict where the worst winds will fall within a few hours time.

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