18 January 2008
Is La Niña to blame for the poor weather and the flooding? Climate expert Dr Adam Scaife explains.
Although not completely responsible there are links between La Niña and mild, wet and windy weather in our region in late winter.
La Niña is a marine phenomenon which cools the equatorial seas of the Pacific, especially towards South America. As La Niña takes hold the main focus for warm rising air shifts to the west Pacific, which has an impact on the atmosphere. This impact travels out of the tropics and interacts with the jet stream - a ribbon of very strong winds in the upper atmosphere which largely determines where the weather systems that bring rain to the UK will develop and move across western Europe.
This year's La Niña is likely to turn out to be the strongest since 1988-89, about 1.5 °C (2.7 °F) cooler than normal, thus having an increased effect on the jet stream. The strengthened jet stream helped to develop more powerful wet and windy depressions, which it then steered across the Atlantic. This week the jet stream has brought those depressions across the south-west of England – in almost exactly the same areas as in the summer.
La Niña, and its opposite El Niño, are two of the elements taken into consideration in our seasonal forecast and conditions so far this winter have been consistent with the outcome we predicted as most likely.