7 Oct 2014

Why autumn delivers stormy weather

Yesterday saw autumn’s first bout of stormy weather affect northern and western parts of the UK, as a deep area of low pressure sat to the north west of Scotland.

The combination of cloud, rain and gales was a shock to the system, following the driest September on record and a summer that has delivered an abundance of sunshine and warmth.

The strongest gusts of wind were recorded in western parts of Scotland, with South Uist on the Western Isles reaching 84mph and Altnaharra, Highland 78mph.

But what makes autumn a season that delivers us some of our stormiest weather of the year? 


Jet stream powers up

The jet stream is the fast-moving ribbon of air around five to six miles up in the atmosphere that determines the weather that we experience at the surface.

jetstream_uk_WZ_wpIt travels around the earth at mid-latitudes, travelling from west to east at speeds as high as around 200mph, driven by the temperature contrast between the poles and the equator. The greater this temperature contrast, the faster the jet stream and thus the more unsettled the weather.

The reason for this temperature contrast increasing in autumn is due to the nights becoming longer than the days in the northern hemisphere, leading to more hours of the day with energy escaping the earth’s atmosphere than entering it – causing a build-up of cold air at the north pole.

As the jet stream acts a conveyor belt for low pressure systems that form over the Atlantic ocean, it not only develops them, but pushes them towards us.

Great Storm of October 1987

In the past, there have been a variety of severe storms that have hit the UK during the autumn months of September to November, but the most notable of them all was the Great Storm of 1987.

The focus of the damaging winds and destruction on 15-16 October 1987 was concentrated across south eastern parts of England.

Gusts of wind as high as 115mph caused the deaths of 18 people, destruction costing around a billion pounds and blew down an estimated 15 million trees.

It was the worst storm to hit since 1703 and was said to be a one in 200 year storm for southern Britain.

St. Jude’s day storm of October 2013

The most recent severe autumn storm to hit the UK was on 28 October 2013. Referred to as the St. Jude’s day storm, it tore across southern parts of England.

Gusts of wind widely reached 58-69mph over southern England, with gusts of 69-81mph across south east England. The highest wind gust of 99mph was recorded on the Isle of Wight.

This storm led to the deaths of four people, severe disruption to transport networks and 600,000 homes to be left without power.

Whilst not on the same scale of the October 1987 storm, it was deemed by the Met Office to be within the top 10 most severe autumn storms to affect southern England in the last 40 years.

At the moment, there are no severe storms in the forecast, but even so, the coming days will bring enough wind and rain to remind us that autumn is definitely here.

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

PS – there’s no snow expected anytime soon!

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