2 Jan 2014

Why have the past few weeks been so stormy?

The past few weeks have seen the UK battered by storm after storm, causing widespread disruption across the country and bringing misery to tens of thousands of people through the festive period.

Severe gales have ripped down trees and power lines, causing major travel disruption and leaving many homes without electricity.

In addition, heavy rain has left the ground saturated and unable to soak up any more water, which has meant that surface water and river flooding have become an ongoing concern.

Pre News refresh player – this is the default player for the C4 news site – please do not delete. Ziad

With no let up in the stormy weather for the next week or so, things may get worse for some before they get better. But why has it been so stormy?

Super-charged jet stream

The jet stream – the fast-moving ribbon of air five miles above the surface that determines the weather we experience at the surface – has been very active during the last fortnight.

It has been racing across the Atlantic Ocean at speeds of around 230mph, which is about as fast as it gets for sustained periods of time.

low_pressure_metoffice_wpThe jet stream interacts with temperature differences and plumes of moisture at the surface, sucking air upwards like a vacuum – leading to air rushing in to replace it, forming areas of low pressure.

With the jet stream being so fast at the moment, this process is happening frequently and vigorously, resulting in areas of low pressure that are deep and stormy.

Not only does the jet stream create these storms, it also acts as an atmospheric highway, catapulting them towards us one after another.

So, when the jet stream eventually slows down, the areas of low pressure will be more infrequent and not as deep.

What’s causing such a fast jet stream?

The jet stream is caused by the temperature contrast between the cold pole and warm equator, with the jet stream following the zone where the greatest temperature difference occurs over the shortest distance.

During autumn and winter, this zone tends to be at mid-latitudes in the northern hemisphere, making the UK and north west Europe prime targets.

What has made the jet stream even more powerful during the past two weeks is that there has been some extremely cold Arctic air flooding off eastern Canada – where daytime temperatures have struggled to get above -20C.

This extremely cold air has been colliding with warm, sub-tropical air and producing a temperature contrast that is much greater than normal – resulting in a jet stream that is persistent and powerful.


Image showing very cold air (blue/purple) colliding with warm air (yellow/orange) over Atlantic Ocean

Are there any signs of the jet stream slowing down?

In recent days, there have been hints that the jet stream will weaken and meander around more towards the middle of the month.

This would result in the weather turning more settled, with fewer storms and a better chance of high pressure building, with lighter winds and less rain.

However, in the meantime, heavy rain, gales and the risk of flooding remain. So, keep an eye on the latest forecast on the Channel 4 Weather website. I’ll also be posting updates on Twitter – @liamdutton

Images: Met Office and Wetterzentrale

Tweets by @liamdutton