17 Oct 2013

Southerly jet stream means a wet and windy outlook

Having just moved into the second half of October, there’s no denying that autumn is well and truly underway.

Leaves are turning on the trees, we’ve had our first widespread chill and there’s just two weeks until the clocks go back and British Summer Time officially comes to an end.

Thankfully, for mine and everyone else’s sanity, we had a summer this year – and a good one it was too. But, as the nights draw in, thoughts lie ahead as to what winter may bring.


A tabloid newspaper has already published the first doom and gloom headline about the forthcoming winter, claiming that it is going to be the worst in decades.

However, unfortunately, similar headlines are pushed out every year and the truth is that no one knows what winter holds. It is simply too early to tell.

Southerly tracking jet stream

As we know, the jet stream – the fast-moving ribbon of air five miles above our heads – drives the weather that we experience at the surface. So, if it changes position, then the weather does too.

The jet stream is driven by the temperature contrast between the cold poles and warm equator, with its path marked by the zone of greatest temperature contrast at mid-latitudes.

sunrays_atmopshere_g_wpIn the northern hemisphere at this time of year, the nights are longer than the days, so there is a net loss of energy because there are more hours of the day with energy leaving the atmosphere than there are entering it.

It’s this net loss of energy that allows rapid cooling to take place at the poles, with signs of this cold air seeping southwards towards places like Scandinavia and Iceland.

As this cold air seeps southwards, it means that the zone of greatest temperature contrast between cold and warm air also moves southwards, thus shifting the jet stream on a more southerly track too.

This is what is happening at the moment, with the jet stream sitting just to the south of the UK for the next ten days or so, with a trend to picking up speed.

What weather will this bring?

With the jet stream sitting to the south of us, it means that some typical autumn weather is set to arrive on our shores in the coming ten days.

windy_coast_g_wpAreas of low pressure will form in the Atlantic to the south west of the UK and then get catapulted towards us by the jet stream.

This means that the general theme is wet and windy, although in between low pressure systems there’ll be occasional drier and brighter days with sunshine.

One good thing about the weather coming from the south west is that it bathes the country in mild air, so at least for now many of us will avoid a chill.

Don’t forget, you can get the latest forecast on the Channel 4 Weather website. I also post regular updates on Twitter – @liamdutton

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