9 Dec 2014

Ten things you need to know about Wednesday’s weather bomb

1 – When will it arrive?

The stormy weather will arrive late on Tuesday evening across the Western Isles of Scotland, before spreading to the rest of Scotland, Northern Ireland and northern parts of England and Wales on Wednesday morning.

2 – How long will it last?

Once the stormy weather sets in across northern parts of the UK, it is expected to last through much of Wednesday, before the winds gradually ease during Thursday morning.


3 – How strong will the winds be?

The strongest gusts of wind will be around 80mph for the north coast of Northern Ireland, as well as northern and western coasts of Scotland.

Northern Ireland, the rest of Scotland, along with northern parts of England and Wales will have gusts of 60-70mph.

For the rest of the UK, it will be windy with gusts of 45-55mph in places, but the winds are unlikely to be disruptive as they will be further north.

4 – What will the impact be?

The latest Met Office warnings highlights that the stormy weather will bring the potential for disruption to power ukwarning_9thDec_MO_wpsupplies and travel.

There is also the possibility that some trees could be damaged. However, with many trees now leafless, they tend to be less prone to getting blown down than in autumn, due to not having leaves acting as sails to catch the wind.

The stormy weather is also expected to generate some very large waves, which will bring the risk of localised coastal flooding to the north coast of Northern Ireland, as well as northern and western Scotland.

5 – What does the storm look like?

The satellite image below from Eumetsat shows a huge swirl of cloud passing close to Iceland. This is cloud is rotating around the centre of the storm, which is heading our way.

It’ll pass to the north of Scotland, with very strong winds on its southern side – hence why we are going to experience the severe gales.


6 – What has caused the storm?

At the moment over the mid-Atlantic, warm sub-tropical air is colliding with cold arctic air, which is causing a huge temperature contrast – something that drives the jet stream.

atlantic_tempcontrast_WZ_wpThe larger the temperature contrast, the faster the jet stream moves; and the faster the jet stream moves, the more active the weather tends to be.

Such a fast-moving jet stream acts as a vacuum in the sky, sucking up air from the surface, causing pressure to fall and a storm to form.

The jet stream is not only responsible for spawning these storms, but also pushing them towards us, on what can be thought of as an atmospheric superhighway.

7 – Why is it being called a weather bomb?

The term weather bomb relates to how rapidly a deep area of low pressure forms. As has been the case with this storm, when its pressure falls more than 24 millibars in 24 hours, it meets the criteria to be called a weather bomb.

The same process is also known as explosive cyclogenesis, which makes sense when you break up the term;

Explosive – something violent or hostile

Cyclo – something circular

Genesis – the formation of something

8 – Will more storms follow?

The next week will see further areas low pressure bring the risk of gales, heavy rain and some snow.

However, at the moment, it is difficult to pin down any detail on their precise track and strength, which is why it is a good to keep a close eye on the forecast in the coming days.

9 – Will there be any #uksnow?

Yes, there will be some snow during the next week – mainly over the hills and mountains in the north of the UK.

However, there is a risk of snow falling at lower levels in the north of the UK at times, with bursts of colder air coming in on the back side of low pressure systems.

10 – Is this unusual for this time of year?

It’s not unusual to get this type of storm forming at this time of year, with the clashing of cold and warm air in the mid-Atlantic driving a powerful jet stream.

We only have to think back to last year, when storms battered the UK all winter, giving the wettest winter on record and severe flooding. However, a repeat of this seems unlikely at the moment.

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

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