What the jet stream means for the UK weather forecast this week

Britain could face travel disruption and see damage to buildings from Thursday onwards as Storm Eowyn lashes the UK.

Strong winds are forecast to hit the UK this week. (PA)
Strong winds are forecast to hit the UK this week. (PA)

A strengthened jet stream is driving severe weather towards the UK later this week, with strong winds of up to 90mph forecast.

After grey but settled weather earlier in the week, Britain could face travel disruption and see damage to buildings from Thursday onwards as Storm Eowyn lashes the UK.

It’s all due to the weather in North America and the changing jet stream, according to the Met Office.

The Met Office said: "The change in conditions is being driven by the weather over the other side of the Atlantic. A large, very cold pool of air over parts of North America is generating a stark contrast in temperatures across the continent.”

This is driving low-pressure systems (which cause bad weather and storms) across the Atlantic towards Britain. It includes a low-pressure area strengthened by a phenomenon called explosive cyclogenesis, which is sometimes referred to as a "weather bomb".

Jet streams take the form of strong winds around five to seven miles above Earth’s surface, and have a large impact on the planet's weather.

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The jet stream that impacts the UK flows from east to west, and small changes in the east can lead to big changes in the weather over the British Isles, contributing to why the weather is so unpredictable.

It flows around the same level international aircraft fly, meaning that flights with the jet stream are typically faster, and those against it are typically slower.

The jet stream can affect weather, in particular intensifying low-pressure systems, which can bring stormy weather, rain and wind.

In some cases, it can act like a vacuum cleaner, sucking the air out of the top of low-pressure systems, causing the pressure to drop even further and worsening the weather, according to the Met Office.

When pressure is low, air rises and cools, and water vapour condenses creating the conditions for strong wind and rain.

This week, the Met Office said that a pool of cold air over North America is “acting to strengthen the jet stream, resulting in deeper low-pressure systems being able to develop.”

Tuesday will see settled, grey weather across the UK, with rain arriving in southern England on Wednesday - before things turn nasty, with the arrival of Eowyn.

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On Thursday, heavy rain will sweep areas in North Wales and Northwest England - and a deep area of low pressure will have deepened rapidly while crossing the Atlantic.

By Friday, strong winds up to 90mph and heavy rain will affect many areas, with yellow weather warnings covering parts of the UK.

Met Office Deputy Chief Meteorologist, Chris Almond, said: “A very deep area of low pressure will bring a very unsettled, potentially disruptive, spell of weather to the UK through Friday and into Saturday. Winds will begin to strengthen on Thursday night with the peak gusts forecast through Friday in Northern Ireland and western Scotland. The wind will also be accompanied by heavy rain bringing some unpleasant conditions to end the week."

Part of the reason the weather will be so unpleasant is due to explosive cyclogenesis.

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Almond said: "As the low develops over the Atlantic and interacts with the jet stream it will rapidly strengthen, a phenomenon called ‘explosive cyclogenesis’, where the central pressure of a low at latitudes in which the UK lies drops 24 millibars or more in 24 hours.

"This is forecast to happen on Thursday while the system is out over the Atlantic and it will be a mature feature by the time it reaches the UK."

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