Now that summer has finally drawn to a close I thought I would look at how the astronomical summer finished in the Central England Temperature [CET] series. The mean CET of the astronomical summer was slightly higher than that of the meteorological one (1st June – 31 August) at 16.70°C, or +1.36°C above the 1961-1990 long-term average, which made it the warmest since 2006, and the 19th warmest in the daily series that started in 1772. A couple of caveats to all this are (1) the values are based on September provisional values (2) I use fixed dates in my climate statistics for the seasons, so summer starts on the 21st of June and ends on the 20th of September, and yes I do know that the date and time of the equinoxes varies.
Ranked on night-time minima the summer of 2016 was joint 3rd warmest. So it looks like the higher number of warm nights and the high mean minimum CET bolstered up the final mean CET of the summer. Not all years are like 2016 where the mean maximum anomaly is matched by the mean minimum anomaly. If you look at the above graph the blue diamonds indicate where four new highest minimum CET records were broken during the summer.
The table below shows a count of when maximum daily CET was equal to or exceeded 25, 26.7 or 28°C. There were only 8 days when the maximum daily CET was 25°C or higher during the summer of 2016. Interestingly, the summer of 2013 had double that number of days but a slightly lower mean (16.24°C), but that again can be explained by the mean minimum in 2016 which was +0.93°C higher than in 2013.
I have just downloaded the gridded 1910 data series from the Met Office for August so that I can have a look at the 2016 summer index across the country. I require that sunshine, rainfall and temperature gridded data so I can calculate the monthly terciles and quintiles values that are used to calculate the summer index. The summer is of course the meteorological summer and consists of the months June, July and August. The table below is the summer index for the whole of the UK, and as you can see summer 2016 index was +10 which is above average and much better than last year, but comes only joint 19th best since 1929.
UK Summer [JJA] Index 1929 – 2016
The picture is much better when you look at the regional summer indices that I’ve also calculated and ranked. East Anglia comes top with an index of +25 just ahead of southern England with +20. Incidentally, in East Anglia summer 2016 was also the best summer index since 1995. No region in Scotland fared particularly well this summer with summer indices of around average (remember the best summer scores 48 and the worst summer -48 using the summer index formulae). You can find more details about the summer index in an earlier article I wrote earlier this year.
Best Summer Index [JJA] in 2016
Daily CET Summer [JJA] 2016
It looks like Summer 2016 was the warmest in Central England since 2006 with a mean temperature of 16.43°C which was +1.08°C above the long-term average (1961-1990). Surprisingly no maximum records were broken during the summer but two high minima were.
Warmest Summers 1659-2016
In the bigger scheme of things Summer 2016 was the joint 27th warmest since 1659 based on mean temperature.
Summer mean CET & anomaly 1659 – 2016
I thought that I would revisit my application that processes rainfall statistics from SYNOP observations and look at the recent dry spell that as affected the south of England for so much of the summer. I’ve just added some extra code to calculate the total number of dry days and the current number of days since any meaningful rain. If you start looking into what constitutes a ‘meteorological’ drought on the internet I’ll warn you it’s very confused! There is a good Wikipedia article on the subject and I’ve decided to use the one in their that specifies 15 days or more with less than 0.2 mm of rainfall in a day. The programs flexible so I can set any threshold so let me know if you have a better definition.
I can’t remember a period when so many fronts have delivered so little rainfall. I know there has been no shortage of fronts, it seems to have been a summer like a lot of others, with continuous switching between tropical maritime and polar maritime air throughout, even if the number of fronts in the Met Office analysis does seems a little bit overdone at times. As you can see from the table below we are fairly close to another drought in a good part of central southern England, I say another, because there was probably another drought in places that occurred during July. The second column from the right shows how many dry days (<0.2mm) there have been in the last month (31 days) which also shows how seriously dry it’s been, with some places such as Odiham having 26 out of 31 dry days. These values are at best an estimate, because as good as OGIMET is there are always missing observations or observations without a rainfall group. This could be easily fixed by the powers that be, and then we wouldn’t be totally reliant on other countries providing the latest daily climate information for the UK, but I won’t go into that (again)!
Number of days since rain – 14 August 2016
Current drought days count
Number of dry days in last month
Driest Places Estimated Accumulated Precipitation 00 UTC on 15 July 2016 – 12 UTC on 14 August 2016 WMO Block 03
Interesting to see that the lovely warm spell that we experienced at the beginning of May in the south of the UK produced the highest hourly mean 24 hour temperature at Heathrow Airport so far this year! It’s funny how we forget good weather in any season very quickly. The way this summer is going May 8th might end up being the warmest of the year, but I have great hopes for September.
The only reason that I noticed this alarming fact is that I was reworking some old code into a new application and was using Heathrow as my test site for hourly SYNOP data. There were a couple of hours missing in the sequence, but one hour was at 00 and the other at 17 UTC so they probably cancelled out any effect that they might have had on the mean temperature. Sorry I had to borrow a line and give it a little twist from Richard III, but I was struggling with a title and a bit of William Shakespeare somehow sprang to mind.
The new application sits on the desktop a bit like a widget and looks something like this:
The idea is so that I can keep an eye on any available SYNOP by means of their latest plotted observation, and because the widget will automatically update you could also set up threshold alarms for temperature, rainfall intensity or visibility, the sky (or maybe the cloud base) would be the limit. Wouldn’t be great to get your hands on the one minute MMS data that the Met Office have and do it properly, because by the time that you flagged up an event using hourly data it would have long past.
Here is some of the output from the application, the graphs are still work in progress.
Thermograph for London Heathrow [7 Apr-15 Jul 2016]
Observations for London Heathrow [7 Apr-15 Jul 2016]
Plot Grid for London Heathrow [7 Apr-15 Jul 2016]
Sunshine for London Heathrow [7 Apr-15 Jul 2016]
Hyetograph for London Heathrow [7 Apr-15 Jul 2016]