28 Jan 2013

Speedy jet stream to give a stormy week

Following a fortnight of cold weather across the UK which brought many places significant snowfall, this week will see a very different weather pattern.

Low pressure after low pressure will arrive on our shores in the coming days, bringing milder air, heavy rain and very strong winds. In fact, at times, it could turn stormy – especially in northern and western areas.

The cause of the change to more unsettled weather is the jet stream – the fast moving ribbon of air high up in the atmosphere that determines how weather systems develop and where they go.

After two weeks of a blocking area of high pressure over Scandinavia deflecting the jet stream away from us, this has now receded, leaving the jet stream to determine our weather fortunes once more.

This week, it’s going to reach speeds of around 200mph and sit over or just to the south of the UK. As a result, active areas of low pressure will be steered towards us frequently – bringing stormy weather.

Heavy rain and flood risk

Whilst all parts of the UK will see heavy rain this week, western areas will see the most.

During the next five days, Wales and the western half of England and Scotland could see 50-70mm, with 100-120mm possible over the hills and mountains.

Given the fact that the ground is still saturated from all the rain that we had during last year, there is a risk of river and surface water flooding – especially in low-lying areas.

An added problem from recent days has been the rapid thaw of the snow that fell last week, which has led to a rise in river levels as the excess water quickly flows into the river catchments.

The latest Environment Agency three day flood risk forecast has Wales, south west England and the west Midlands at greatest risk of river and surface water flooding in the coming days.

Strong winds

Much of this week will be windy, with gales likely – especially around the coasts and across the hills.

However, there looks to be a particularly stormy spell for Scotland and the far north of Northern Ireland later on Tuesday into Wednesday.

Gusts of wind could reach 50-65mph quite widely, with northern and western parts of Scotland having gusts of 70-80mph for a time on Tuesday night, leading to potential disruption.

Melting snow from space

Finally, I thought I’d share these stunning images (below) of snow cover across the UK on Saturday (top) and Sunday (bottom), captured by NASA”s rapid response satellite.

The images have had a filter applied which makes snow cover show up in dark red. You can see that in just 24 hours, the arrival of milder air and heavy rain melted the snow very quickly, turning the landscape back to green.

NASA image – snow cover (dark red) on 26th January

NASA image – snow cover (dark red) on 27th January

If the weather causes any problems where you are this week, please get in touch on Twitter – @liamdutton

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