22 Sep 2014

September: driest start in over half a century

The first half of September has been very dry across the UK, with temperatures well above average, according to provisional Met Office statistics up to the 15th day of the month.

This was in stark contrast to August, which was a very wet month across the UK, with rainfall 56 per cent above normal.

The reason for each month being dominated by one particular weather type was due to the jet stream sitting in roughly the same place for extended periods of time. 

harvest_field_g_wp

During August, the jet stream was over or just to the south of us, steering low pressure and rain our way. However, much of September has seen the jet stream north of us, allowing high pressure to build.

Driest start to September for 50 years

Figures up to the 15 of September show that there has been just 6.7mm of rain across the UK, which is just 7 per cent of the monthly average of 96mm.

At this point in the month, we would typically expect around half of the average rainfall to have fallen.

This lack of rainfall makes it the driest first half of September the UK has seen in available records that go back to 1960.

It’s also the driest start to September for Wales, Scotland and Northern Ireland, but not England, when 1997 and 2003 were drier.

September warmth

aberdeen_sunshine_g_wpNot only has the first half of September been dry, it has also been warm across the UK, with the mean temperature (an average of day and night temperatures) 1.3C above average.

Whilst night time temperatures have only been a little above average (by 0.7C), it has been the daytime temperatures that have exhibited marked warmth, at 1.9C above average.

On 18 September, a temperature of above 25C was recorded in the UK for the first time since 8 August, with 25.8C at Northolt in west London – almost 10C above what would normally be expected.

What about the rest of September?

The next few days will see the weather temporarily turn unsettled, as high pressure topples for a time, allowing weather fronts to move in off the Atlantic.

greysky_hills_g_wpThis will lead to a change to cloud, rain and brisk winds for a time – especially for northern and western parts of the UK.

Despite this blip to something unsettled, it looks as though high pressure will build across us next weekend, with a return to largely dry weather with some sunshine.

However, with the autumn equinox taking place at 3.29am tonight, the nights will soon be longer than the days.

This will result in more time in the day with energy leaving the earth’s atmosphere than entering it in the northern hemisphere, meaning that under high pressure, clear skies and light winds, increasingly chilly nights and mornings are to be expected.

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

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