Summer 2015 weather: like or dislike?
With the calendar page flipping over into September, today marks the beginning of meteorological autumn.
In the past few weeks, you can’t fail to have noticed the days getting shorter, as darkness arrives a few minutes earlier each evening.
As the hours of darkness over the Arctic increase, temperatures there will start to fall quickly, which will increase the temperature contrast between there and equator.
It’s this temperature contrast that drives the jet stream and as this increases further into autumn, the jet stream will strengthen, bringing us rain that will drench us at the bus stop and wind that will blow leaves off trees.
However, having said this, you’d be hard pushed to notice the difference between August and the start of autumn, given how disappointing the weather has been lately.
Summer 2015 – cooler and wetter than normal
Provisional figures from the Met Office show that summer – June, July and August – has been a little cooler and wetter than normal.
For the UK as a whole, rainfall has been 13 per cent above normal, with temperatures 0.4C below normal.
So whilst not a record breaker by a long stretch, the theme of generally unsettled weather is clear.
Despite the generally cool and unsettled theme, the short spell of heat at the beginning of July was enough to send the mercury soaring to 36.7C at Heathrow airport on 1 July, making it the hottest July day on record in the UK.
Why such disappointing weather?
As is often the case, the disappointing weather has been down to the jet stream spending much of this summer over or just to the south of the UK and moving a bit faster than normal for the time of year.
This has put us in the path of areas of low pressure that have formed over the Atlantic Ocean and then been pushed towards us.
One reason that has probably caused the jet stream to behave this way is that sea temperatures in the north Atlantic Ocean are 2C below normal.
Just as warmer than average sea temperatures warm the air above, cooler than normal sea temperatures cool the air above.
As the jet stream is driven by temperature contrasts between cold and warm air, this colder area will have enhanced the contrast, giving the jet stream more oomph.
Any signs of more settled weather soon?
This week will stay cool and showery as an area of high pressure just to the west of the UK puts us in a chilly northerly wind.
However, next week, this area of high pressure will drift over us, not only giving drier weather and some sunshine, but also bringing warmer air and rising temperatures.