Sunday, April 7, 2013

Why the UK's turbulent weather is getting even harder to predict

Robin McKie in the Guardian (UK): ...The persistence of the spring's grim weather is particularly striking for it comes after a series of other extreme meteorological events in recent years. Last winter, a severe drought triggered stern warnings by the Environment Agency that water rationing and hosepipe bans would soon have to be introduced – until several months of torrential rain produced widespread flooding.

Our weather, always unpredictable, is now fluctuating on a grand scale and becoming increasingly hard to forecast long-term. The challenge for meteorologists is to explain these unexpected outbreaks of climatic unpleasantness.

"There is no doubt that the recent weather has been highly changeable – on both sides of the Atlantic," said meteorologist Nicholas Klingaman of Reading University. "We have blizzards and flooding. America has had droughts and scorching temperatures."

Nor is it difficult to pinpoint the immediate cause, Klingaman said. The problem lies with the jet stream, a narrow band of strong winds that sweeps round the planet between the tropics and the Arctic. "Its behaviour has changed dramatically in the past few years and has produced these lengthy bouts of extreme weather. The real question, of course, is an obvious one: why has the jet stream changed its behaviour?"...

A storm-damaged seawall in the UK, 2010, shot by Evelyn Simak, Wikimedia Commons via Geograph UK, under the Creative Commons Attribution-Share Alike 2.0 Generic license

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