How a band of cloud separates autumn and summer

As September gets underway, there’ll be an ongoing battle for supremacy between summer and autumn. Who wins will have a huge impact on how the weather feels in the coming weeks.

The reason that I chose to write about this today is that the weather during the next few days is a classic example of how band of cloud, marked by a cold front, separates the heat of summer and the chill of autumn.

At the moment, there’s a band of cloud stretching from the Azores all the way to Scandinavia – clearly visible on the satellite picture below.

This cloud marks where weather fronts lie – the dividing line between cold air to its north and warm air to its south. Effectively this boundary separates autumn and summer.

As the jet stream – the fast-moving ribbon of air five miles up in the atmosphere that drives our weather at the surface – is driven by contrasts in temperature, this band of cloud also marks its current path (white arrows below).

The jet stream acts as a conveyor belt for pushing air of different temperature and humidity around our planet.

When it heads northwards, it scoops up warm air from the tropics ahead of it and when it heads southwards, it scoops up cold air from the poles behind it.

This is why the position of the jet stream is so influential in delivering the weather that we experience each day.

In the coming days, it’ll mean that after a brief spell of temperatures approaching 30C in eastern parts of England, they’ll be back down to 20C at the weekend.

The rest of the UK will be even cooler at 14-18C – a taste of autumn will most definitely be in the air.

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

Satellite images: EUMETSAT