16 Dec 2013

Fast-moving jet stream to bring gales, heavy rain and flood risk this week

Following a recent spell of settled weather, this week will see low pressure after low pressure arrive on our shores, bringing heavy rain and gales.

Whilst it’s not unusual to have stormy weather at this time of year, the coming week and beyond is looking very lively – especially for north western parts of the UK.

This change is due to the speed and position of the jet stream – the fast-moving ribbon of air five miles up that determines the weather that we experience at the surface.

stormy_lighthouse_g_wp

Not only is it moving further southwards this week, it is also going to pick up in speed, reaching 220mph at 30,000ft – about as fast as it gets.

The reason for this super-charged jet stream is very cold Arctic air from Canada colliding with tropical air from the Caribbean.

As the jet stream is driven by temperature contrasts, such a large difference in temperature over a relatively short distance is making it particularly powerful.

This jet stream is then acting as a conveyor belt for developing deep areas of low pressure and catapulting them towards us – one after another.

Heavy rain and flood risk

The next five days are looking wet for much of the UK, but western areas are likely to see the greatest amount of rainfall.

Here, 20-40mm of rain is expected widely, with the hills of Wales and western parts of Scotland and England having as much as 50-100mm.

River levels can respond quickly to heavy rainfall during the winter months, as water swiftly runs off the land and into river catchments – potentially causing flooding.

Whilst the latest Environment Agency three-day flood forecast doesn’t highlight a particular flood risk at the moment, I expect this to change as the week progresses.

Very strong winds

Another notable feature of the weather this week will be the strength of the wind. As deep areas of low pressure pass to the north west of the UK, gales or even severe gales are likely.

Of particular concern is a nasty storm that passes just to the north west of the UK later on Wednesday and into Thursday.

fallen_tree_g_wpWhilst there is still some uncertainty about the exact path of the storm and the strength of the winds it will deliver, the potential is there for damage and disruption for Northern Ireland, along with northern and western parts of Scotland.

The Met Office has issued a warning for gusts of wind of 60-70mph, with a few places reaching 80mph. This has the potential to bring down trees and disrupt transport.

However, at the moment, with the worst of the winds expected during Wednesday night, it may well be the case that disruption may not be on the same scale as it would be if the peak winds hit during the daytime. Nevertheless, it’s one to keep a close eye on.

Even away from these areas, wind gusts in the range of 40-60mph are likely elsewhere, which will make for tricky travel in the run up to Christmas.

As always, you can get the latest forecast on the Channel 4 Weather website. I’ll also be tweeting regular update on Twitter – @liamdutton

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