Autumnal weather is finally on the way

September has been somewhat of a treat following the wet and cool August that we had. As well as being warmer than average, September has also been very dry.

Met Office provisional figures for the first half of the month showed that the UK has had its driest start to September in just over 50 years.

The reason for the dry, settled weather is the position of the jet stream. For much of September, it has been sitting to the north of the UK. 

This has allowed a blocking area of high pressure to become established over us, stopping rain-bearing weather systems from moving in off the Atlantic.

Changing fortunes

However, our fortunes are finally going to change this week, as the weather finally delivers us a reminder that we are well and truly into autumn.

As I mentioned in my blog last week, having passed the autumn equinox, the nights in the northern hemisphere are now longer than the days.

This means that there is increasingly more time each day with energy leaving the earth’s atmosphere in the northern hemisphere than entering it.

Therefore, cooling is taking place towards the poles, which will strengthen the temperature contrast at mid-latitudes, causing the jet stream to power up.

Jet stream heading south

During the next week, the jet stream is not only going to pick up speed, but it is will also start to move further southwards.

It’ll dip down across Scotland and Northern Ireland later this week, before dipping south of England and Wales next weekend.

This will see the balance of power shift from high pressure to low pressure, bringing a change to weather that is much more akin to autumn.

Wind, rain and cooler air

Scotland and Northern Ireland will be first to see the change to brisk winds, rain and cooler air by Wednesday. In fact temperatures will only reach the mid-teens by this point, falling further to just 9-13C next weekend.

Much of England and Wales won’t really feel the effects of a change to autumnal weather until next weekend, when wind, some rain and temperatures of 12-17C will arrive.

Looking further ahead into next week, it looks like low pressure is going to get stuck over us, giving a theme of showers or longer spells of rain for most.

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