Summer 2016 turned out to be a very decent season overall, the mean temperature of 18.7C (1.1C above average) made it the sixth warmest summer since 1797.
While it wasn’t quite up there with the hot summers of 1976 and 2003 it still produced some notable records. The stormy beginning to June effectively ended with the Brexit vote, a period of 24 hours that coincided with the highest daily rainfall this area has seen since at least 1959.
The multi-cell thunderstorm in the early hours of June 23rd produced 60.8mm of rainfall, nearly half of the month’s total which became the third wettest June in a record going back to 1797. The high rainfall was in complete contrast to July and August and helped skew the overall figure: 168.6mm is 114 per cent over average summer rainfall.
With so much rainfall overall sunshine was affected with only 451 hours recorded, just 80 per cent of what can be expected in an average summer.
July produced another record, this time the highest overnight minimum recorded since 1959. The minimum of 21.1C was recorded during the early hours of the 20th – coming hours after the hottest day of the year: 33.5C – the 14th hottest day on record.
The warm and very dry theme continued into the final month of summer with the warmest August for 12 years, the 10th warmest and 12th driest since 1797.
My summer forecast, when the monthly probabilities are considered, was broadly correct though I didn’t estimate correctly just how warm it would be.
The cold start to June may soon be a distant memory once summer proper gets going in east London. But rather than a succession of prolonged hot, dry spells it’s looking like the season overall will be broadly average – you will hear the old saying: ‘an English summer consists of three fine days and a thunderstorm’ more than once this year.
Looking at summers back to 1799 I’ve tried to find a pattern linked with a declining El Nino. And failed to find anything conclusive. With ENSO forecast to be approaching neutral by August I decided to discount it completely, instead relying on pattern matching of meteorological data from this area for March, April and May stretching back to 1799.
The mean for the spring season was 10C with 156.4mm of rain and 455 hours of sunshine.
If you take into account all years that were within +/- 10 per cent of these figures, for rainfall and then mean temperature, some 36 ‘best fit’ years emerged, far more than my previous two attempts to forecast summer. The years, ranging from 1805 through to 2007, saw all manner of summers – only one was a real corker, 1825, but most were fairly nondescript average affairs. As an average this summer could be expressed as: Mean: 16.7C (just above average) Rainfall: 166mm (exactly average) Sunshine: 546hrs (about average)
Or, expressed in probabilities, I concluded the following:
From the above you could deduce that the next three months will be slightly warmer than average, with average rainfall and sunshine.
Last year I tried to decipher, with fair success, when hot spells would occur. However, looking at the data of these 36 summers very warm, dry spells happened through the three months – it was impossible to find any exact pattern to when it would be warm and dry.
Instead I’ve broken down the summer into June, July and August probabilities.
Looking at June, considering this cool and cloudy start, I would guess that we can look forward to a few very warm, thundery spells – a repeat of the Spanish plumes of the past couple of years.
Considering the above data perhaps there is a greater than evens chance of some thundery activity – and the nature of thunderstorms mean you can get a deluge or stay relatively dry / average. Sunshine average.
On to July. After a ‘rather warm’ June I wonder if the ‘return of the westerlies’ will happen just in time to affect this month?
The above chart would suggest that July will be classically average overall. Fine, not too hot spells, with occasional depressions bringing cooler weather and showers.
On to August. This month has been a real disappointment the past couple of years. However, I think this year August may offer a bit more in the way of sunny weather.
Looking at the above probabilities there seems a fair chance of something average to rather warm overall. With rainfall below average and average sunshine I wonder if there will be two or three fine spells throughout August – perhaps more?
So, all-in-all, summer looks a mixed bag. How this summer will fair obviously only time will tell. One could argue that what I’m forecasting is just climatology which has a good chance of being correct should no external influences, such as a huge eruption on Mount Etna, have a bearing on the end result.
* Taking into account the fact that temperatures in London are up to 0.66C warmer than they were 100 years ago I have added 0.66C to mean temperatures before 1915.
** Obviously, in the event of a series of direct hits from thunderstorms, my rainfall estimate could be hopelessly short – a symptom of abundant solar energy at this time of year which creates a ‘noisy’ atmosphere compared with winter.
*** The 1981-2010 average mean for summer in this region is 17.6C, with 144.9mm of rain and 564 hours of sunshine