Monday, 25 August 2008

The Polar Front Jet Stream

I’m using the blogspot facility to pre-post this to be published while I’m away again for a few days. If it works you’ll be able to see it on August Bank Holiday Monday while I’m heading to London by train.

Our local BBC TV news service is Points West. Their resident weather forecaster, Richard Angwin, is very popular. I won’t steal a picture of him but you can find him here.

He always does his best to make his forecasts interesting, giving tips on what we might be able to see passing in space on clear evenings, and so on. Last week he was trying to explain how the reason for all our recent bad weather is the behaviour of the polar front jet stream.

This is a band of wind that separates the mass of warm air to the south and the colder air to the north. It’s the wind that makes a flight time from America to Europe faster than going the other way, when the aircraft would have to make headway against it. The wind usually blows from west to east, the way the earth rotates. But sometimes it can move in a more southerly direction.

The jet stream also brings the weather fronts. And so the reason for all the rain we’ve had recently is that this jet stream is much further south than it usually is at this time of year, bringing us the rain-bearing depressions and storms we’ve had recently.

Unfortunately, after the floods in the dreadful weather here last year, it seems to be setting a trend. No doubt it’s one other thing we can lay at the door of global waming.

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