We’re getting onto halfway through winter now, and I wondered just how well the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy were doing with their forecast for this winter they issued on the 25 November 2024. Well, mean temperatures are +0.7°C above average, that’s despite the ongoing cold spell, but not as mild as the 45% on the mild side of average suggests, so 6/10. Total rainfall also looks higher than average, and higher than forecast with all these flood alerts around at the moment. December was rather dry, particularly in the S, but a forecast of 30% on the wet side of average still looks a little too low, so maybe only 8/10 for that. The UKMO provide no LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. for wind speed that I can find to calculate anomalies with, and surprisingly they don’t forecast sunshine, which is pretty important for the nations vitamin D3 levels. 😎
There are two varieties of CETCETCentral England Temperature data which you can download from the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy, they are the monthly series from 1659, the daily series from 1772 for daily mean temperatures, or the daily maximum and minimum series from 1878. So if you want monthly means in central England, you are either stuck with using ‘meteorological’ seasons by adding up three monthly means to get a seasonal mean, or alternatively adding up 90 or so daily values, and calculating either a meteorological or an astronomical seasonal mean. And that’s what I’ve done with this bespoke viewer which allows you to view any season, be it astronomical, or meteorological, for any year since 1772. It’s a big improvement on using monthly data, because as well as looking at meteorological seasons, I can now view astronomical seasonal means, as well as the latest three months of daily data, or see how the latest season is doing. By the way, you are now deep in weather nerdland with this article. 😜
Autumn 2024 was rather an anticyclonic affair at times, particularly from late October to mid November, punctuated by cyclonic spells through October, and two named storms, Ashley on the 20th of October and Bert, between the 23rd and the 25th of November. It’s hard to beleive there is only one 12 UTCUTCCoordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy analysis chart this autumn, from the whole 91, completely free of fronts of some kind around the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland..
I thought that I’d look back at the three month outlook for autumn 2024 [SONSONMeteorological Autumn - September, October and November] issued by the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy on the 27 August. The outlook is split into three distinct areas, temperature, precipitation and wind speed. It’s relatively easy to assess how accurate the outlook was for temperature and precipitation, but not so for wind because the UKMO don’t issue monthly gridded mean wind speed data. They must have this data because the three month outlook itself contain three month anomaly charts for wind speed. The one climate statistic that they did omit is sunshine, important not only summer, but also in autumn and winter, as this gloomy November highlighted only too well. Here’s a table of climate statistics for the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. for the three months that make up meteorological autumn and anomalies for temperature, precipitation and sunshine.
How accurate was the forecast of temperatures?
The outlook stated that there was a 40% chance of it being a warm autumn, with a fifty-fifty chance of near average temperatures. In the end, the mean temperature for the three months that make up meteorological autumn was +0.3°C above the 1991-2020 long-term average, so it was only marginally warmer. WRONG, autumn was not noticeably warmer than average, although they were right about ‘cool spells’ later in the season, but cold spells towards the end of autumn are far from uncommon.😉
How accurate was the forecast of precipitation?
The outlook stated that there was a 35% chance of autumn being wet, with a 55% of it being near average. In the end precipitation in autumn 2024 ended up 89% of the long-term average. So a drier, rather than a wetter autumn. Despite flooding from storm Bert, the first half of November was very dry across the whole country, WRONG.
How accurate was the forecast of mean wind speed?
The outlook stated that there was a 35% chance of autumn being windier than average, with an increased risk of stormy conditions. As I said earlier, there’s not an easy way of measuring the accuracy of this one. There were three named storms during autumn, one of them named by the KNMI, the other by Met EireannMet ÉireannMet Éireann, the Irish National Meteorological Service, is the leading provider of weather information and related services for Ireland.. The first half of November was anticyclonic which would have reduced the mean speed for the whole of autumn a fair bit. UNDECIDED.
The mean temperature during Autumn 2024 in central England was 10.9°C, which was +0.11°C above the 1`991-2020 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO., making it the joint 21st mildest since 1659 in the series. Autumn 2024 also set three new daytime maxima (red stars) and one nighttime minimum temperature (blue star). All three months had a cold spell, the most significant occurring from the 19th to 22nd of November. Autumns in central England have been gradually warming by around 0.12°C per decade since 1878.
Not a great deal of difference from the results of the Summer index for 2024 really, with East Anglia still having the highest index and Northern Scotland the lowest. The result for the extended summer in Northern Scotland were much improved though, from a summer index of -27 to and extended summer index of -7, thanks to a spell of good weather and record temperatures in May, and another settled warm spell in mid September.
I make the summer of 2024 [JJAJJAMeteorological Summer comprising the months June, July & August] the coldest since 2015, with a mean temperature of 15.77°C, which was 0.27°C lower than the 1991-2020 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO..
Not much to say about summer [JJAJJAMeteorological Summer comprising the months June, July & August] other than it ended up a very average summer. That was because the cooler, cloudier, wetter conditions in the northwest, were almost perfectly cancelled out by the drier, sunnier and warmer weather in the east and southeast.
The summer index [JJAJJAMeteorological Summer comprising the months June, July & August] in the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. for 2024 came in at 11, which was almost the same as last summer. June had the lowest combined monthly index for temperature, precipitation and sunshine of 6 [3,1,2], whilst August bolstered the summer up with an index of 9 [5,2,2].
Regionally East Anglia, the southeast and central southern England and eastern Scotland had the highest summer index of 24. The lowest index, which I can vouch for, was -23 in the north of Scotland.
I’ve never added any animation to my Daily Central England temperature application up until now, so I thought as the weather today is still pretty dreich, I would put that right today. It’s amazing how the simple animated GIF is still going after all these years, it was declared dead many years ago at the same time as Javascript, but it’s simple and produces compact files, and there’s still not anything out there to replace it.
Spring 2024 saw a very warm spell from approximately the 8th to the 20th of May with anomalies across northern Scotland of +7°C, followed quickly by a cold spell, from the 4th to 12th of June with anomalies of -5°C. The Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy thought little of both spells, despite May ending up the warmest since records began in 1883. They argued that the cold spell wasn’t that unusual, or as cold as the temperatures in many recent years, despite the fact that snow fell on ground above 800 M in Scotland for at least five consecutive days. They didn’t seem to want to factor in that the cold spell had occurred at a time when global temperatures were 1.54°C above the pre-industrial age or that North Atlantic SSTSSTSea Surface Temperatures are at record levels. What a strange attitude to take. 😮
According to gridded climate data from the UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy, the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland. was warmer and wetter than average, as well as being warmer and duller than average in Spring [MAMMAMMeteorological Spring comprising the months of March, April & May] of 2024.
I make the mean temperature for spring [MAMMAMMeteorological Spring comprising the months of March, April & May] 2024 in central England 10.6°C, that’s +1.38°C above the 1991-2020 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO., and the warmest spring since the series began back in 1659.
I estimate the first day of spring in Central England this year occurred on the 8th of February, that’s 42 days earlier than the accepted date for Spring of around March 21st depending on the exact date and time of the vernal equinox. That made it the joint seventh earliest spring in the CETCETCentral England Temperature record back to 1772. I use the average number of degree days from 1773 to 1802 to calculate a baseline to estimate the date with. Not a brilliant method. let me know if you can think of a better one. The last late spring, and the only one to occur in this century was in 2010. The linear trend reveals that springs are now arriving 24 days earlier than they did in 1772. Apologies for the late arrival of this story 😉
One of the very first articles that I read in the Weather Magazine as a young outstation assistant was entitled “A simple summer index with an illustration for summer 1971” by R. Murray which was published in April 1972. Now over forty years later, as a retired programmer with the Met OfficeUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy, I have decided to revisit the summer index and update his record. I have a number of advantages that Murray could only dream of, and they are a powerful personal computer, up to date freely accessible climate data, and of course the Internet to access that data from. The Met Office provide the data in the form of monthly regional and national gridded climate data back to 1910. This provides you with all the temperature, rainfall and sunshine that you require to calculate a summer index, and the advantage of this data is that you can generate a summer index not only for the UKUKThe United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland., but for England, Wales, Scotland, Northern Ireland as well as any of the other twelve other regional areas. All that was required to access the latest climate data from the Met Office website was internet access. The program converted the text files I downloaded into a data structure to hold each month’s mean temperature, total rainfall and sunshine values necessary to compute each year’s summer index. The slightly tricky bit was to calculate the quintiles of each month’s mean maximum temperature, and the terciles of the total sunshine and rainfall that the formula requires.
The summer index [SISISummer Index]
SI = 3T + 5S – 5R – 9m
where:-
m = number of months
T = sum over m months of quintiles of monthly mean temperature
S = sum over m months of terciles of monthly sunshine
R = sum over m months of terciles of monthly rainfall
Quintiles and terciles are statistical terms used with any series of data arranged in order of magnitude. Rainfall is conventionally divided into three equal classes; the driest third being tercile 1, and the wettest tercile 3. With temperature the data is divided into five equal classes; quintile 1 refers to the coldest and quintile 5 to the warmest. There is a drawback in using the climate data series from the Met Office, although the temperature and rainfall series extend back to 1910, the sunshine series is only available from 1929, so I was unable to reach back quite to 1881 as Murray did originally. Using Murray’s formula the absolute best ‘meteorological’ summer can score a maximum SI of 48, and the absolute worst a SI of -48.
A simple summer index
The summer index was first proposed by Davis in 1968, its beauty lies in its simplicity, but a good summer can be ruined by a wet last week in Autumn, so the index is far from perfect. You could dream up a summer index that looked more closely at daily values of temperature, rainfall and sunshine, but at the moment the Met Office do not make daily regional climate data available, so for now monthly data will have to suffice. How do you define what constitutes a ‘good’ summer? It is very subjective, and as we grow older, it may have less to do with weather, and more to do with other things that are going on in our lives. Keeping it strictly meteorological, and if you’re older than 70, you probably look back at the summer of 1959 as being the best, older than 50 and it’s highly likely that 1976 will be your perfect summer, younger still and it may well be the summer of 1995 or 2003. The worst summer in contrast is not so easy to quantify, and many people if asked will struggle to name the worst summer that they have experienced in their lifetime.
The ‘best’ summers
As you can see from the table of best summers (fig 1), 1976 tops the Summer index back to 1929 for the UK which probably comes as no great to surprise to many. In fact its score is the perfect maximum of 48.
Fig 1
The extended summer index
The beauty of the algorithm is that you can also calculate an extended Summer index (May through to September), which gives an entirely different slant on what was the best summer. The table below (fig 2) shows that 1959 has the highest extended summer index of 62 (out of a possible 80), and that 1976 is only eleventh in the rankings, with an index of 28. So why was the extended summer of 1976 so much worse? If you compare the various quintiles and terciles for 1976 and 1959, you will see that 1976 was in fact duller and wetter than 1959 in May and September so the extended index score was reduced.
Fig 2
Because the data is also split into regional as well as national values, it’s easy to compare what kind of summer other parts of the UK experienced. As you can see in the breakdown of the extended summer of 1959 (fig 3), the northeast of England and the Midlands score a very high 72, whilst somewhat lower down the rankings came the north and west of Scotland.
Fig 3
The ‘worst’ summer
The summer of 1954 has the lowest summer index -48 of all summers in the UK since 1929 (fig 4), you just can’t get a summer index lower than -48. 1954 was the very antithesis of 1976, it was not only wet, it was cold and dull. Even if you compare 1954 using the extended summer index, it’s still has the lowest index of -64 for the UK. Just to show you how poor that summer was, here are the headlines for each month of the extended summer of 1954 that I’ve copied from the Monthly Weather Report.
May 1954 mainly dull and wet, with frequent thunderstorms; large variations of temperature.
June 1954 mainly dull and cool; periods of rain, heavy at times.
July 1954 notably cool and dull; wet in some areas.
August 1954 cool and dull, mainly wet in England, Wales and southern Scotland.
September 1954 cool and unsettled; wet in most areas; sunny on the whole.
Fig 4
Graphical view
Finally, here is a graphical way of looking at the summer’s since 1929 as a whole by means of two scatter graphs. The first graph plots temperature against rainfall (fig 5), whilst the second graph plots temperature against sunshine (fig 6). They show at a glance just how each summer compares with each other, for instance although 1995 was very slightly drier than 1976, it was slightly less sunny and not as warm.
Fig 5Fig 6
Are summers getting any better?
The one remaining question is – are summers getting better? Well with the help of another chart (fig 8) I’ve plotted the summer index and overlaid it with a five-year centred moving average (dashed line with a yellow outline). I’ve also added a simple linear trend (dashed black line), although climatologically this may be frowned upon (because any trend certainly wouldn’t be linear), it does help to highlight the increase in summer index that there has been since 1929. So the short answer to that question is yes, the summer index has increased over the last 87 years, whether that equates to better summers, I will leave that for you to decide.
Fig 7
References
Davis, N. E.1968. An optimum summer index. Weather23: 305-317.
Murray, R.1972.A simple summer index with an illustration for summer 1971.Weather45:161-169.
Footnote
Many of my regular readers may remember that I wrote an article about the ‘Summer Index’ in July 2015. I fully intended to get a fuller version of it published in the Weather Magazine of the Royal Met Society. I lost heart in the end, I don’t think I write in the way that they like, and I’m not good at writing in any other way. I went to a bit of trouble in putting the article together, so instead of it just languishing in a folder named ‘Weather Magazine’ in my Google drive account, I thought that I’d re-publish it in my blog just for posterity. The other thing that I like about a blog is that you can always fix typo’s or mistakes which you can’t do in a printed magazine, hopefully there are not too many of those.
Winter 2023-24 in Central England was a mild affair with only two main cold spells to speak of. One in the first week of December to start, and another in the second and into the third week of January. I made the mean temperature 6.5°C which was +1.68°C above the 1991-2020 LTALTALong Term Average. This is usually defined as a 30 year period by the WMO. making it the fourth mildest winter since 1659, behind the winters of 1868-69, 2015-16, and 1833-34. Despite this three new record low temperatures occurred, along with nine new record maxima and eight new record high minimum temperatures.
Meteorological Autumn 2023 has seen some quite varied weather types, predominantly anticyclonic until mid October and then full on cyclonic. It also contained four named storms, some of which were more deserving than others for being named. I can’t even remember them all, only Ciaran and Debi stick out. Zonality also did a couple of about faces during October and again towards the end of November.
Just a quick note to make a note about how late an Autumn it’s been in 2023. Its now past mid October, and many trees here in StrathpefferStrathpefferStrathpeffer (Scottish Gaelic: Srath Pheofhair) is a village and spa town in Easter Ross, Highland, Scotland, with a population of 1,469. are still have more green leaves than they do brown, and although the Service and Birch tree have lost most of their leaves, others have not. I witnessed late, even very late Autumns in Devon over the years, but not here in Scotland since we returned five years ago. Why is Autumn late? Simple enough, summer was pushed into September and early October by a rather cold mid-summer as these anomaly charts show. The numbers in the pink boxes by the way are the mean anomalies for the gridded temperatures for the whole map, the graph is for temperatures at the grid point 57.5N 5W, the closest to home. It does make you wonder if meteorological summer should now be a four month period rather than a three which also includes September, whilst Autumn should now include December. By the way the title of that graph should read Mean Temperatures and not anomalies and another thing to put right.
Autumn 1959 MSLPMSLPMean sea level pressure is the pressure at sea level, or, when measured at a given elevation on land, the station pressure reduced to sea level assuming an isothermal layer at the station temperature. & 500 hPahPaA Hectopascal is the SI unit of pressure and identical to the Millibar gph
I can already see a few similarities in the first week of September with the memorable September of 1959. September 1959 had the third longest anticyclonic spell in the whole objective LWTLWTLamb Weather Types are often used in UK-based analyses, with individual weather patterns based on the eight primary cardinal directions (N, NE, E, SE, S, SW, W, NW) plus cyclonic (C), anticyclonic (A) and unclassified (U) types. series that began in 1871. The heatwave in the first week of September 2023 looks poised to break a number of CETCETCentral England Temperature record maximum temperatures that were set in 1959. In 1959 as well as possible heatwave conditions occurring between the 7th and 12th of September in central England, a second warm spell occurred between the 3rd and 7th of October. It will be interesting to see just how anticyclonic September 2023 proves to be, and if November turns out to be as cyclonic as that of 1959.
Autumn 1959 [SONSONMeteorological Autumn - September, October and November] Daily Central England TemperaturesAutumn 1959 [SON] Objective LWTSeptember 1884-2022 Ranked Highest Mean Maximum Temperature
The summer [JJAJJAMeteorological Summer comprising the months June, July & August] consisted of the fifth warmest (mean anomaly +2.4°C) June in central England, followed by the two non-descript months of July (mean anomaly -0.7°C) and August (mean anomaly -0.2°C). You’ll notice that there were no warm spells to speak of after the 25th of June, when the summer switched to average mode. The June 10th to the 16th was a quite remarkable spell, setting 7 consecutive new maximum daily temperatures for June. The rest of the summer also set five new high daily minimum records and one for the lowest minimum on the 26th of July (8.6°C).
Summer started in a very anticyclonic mood with negative zonality (E’lies). The rot soon set in, and by the 19th of June the summer had turned when positive zonality (W’lies) was restored, and that’s basically where we’ve been since then. The meridional index has switched between spells of negative and positive, as it tends to do across our part of the world, and generally cyclonic. There were a couple of days with a gale index above the threshold of 30, but neither tie in with the named storms of Antoni (5 Aug) or Betty (18-19 Aug). The UKMOUKMOThe Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy, in their wisdom, decided not to name the deep low on the 15th of July that produced a GIGIGale Index of 40.5, but I reckon it was the equal of either of the two that were named.
You may have noticed that I’ve put some work into smartening up the front end of my application that visualises objective LWTLWTLamb Weather Types are often used in UK-based analyses, with individual weather patterns based on the eight primary cardinal directions (N, NE, E, SE, S, SW, W, NW) plus cyclonic (C), anticyclonic (A) and unclassified (U) types., the data for which I download from the CRU at the UEA. I’m quite proud of the app, and it works very well. I am so glad that the CRU have kept the objective series going after H.H.Lamb’s death in 1997. I do have the objective LWT algorithm, which I run on six hourly gridded reanalysis data in a seperate application as well , which gives a more detailed view of how weather types unfold.
Fine weather over central & SE England identified by Summer Index
I’ve been toying with the idea of a Real-time summer index [SISISummer Index] for many years. Of course the idea of a summer index is very subjective – everyone’s perfect summer day is different. I use a very simple algorithm of total cloud amount, present weather, relative humidity, surface visibility, mean wind speed and of course temperature to calculate it with. Results look promising. There’s no reason why the idea couldn’t be extended to use NWPNWPNumerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. data for forecasting summer index for many days ahead. The values are using my preferences for an ideal temperature of 25°C. This is not ideal because what I would like to have used was anomalies. A fixed temperature also means the SI will oscillate through the day as things warm up, so it’s far from perfect. A perfect day to me really requires an okta of cumulus or cirrus cloud rather than complete blue skies. The perfect day also requires some wind, no more than five knots, perfect visibility and low humidities. I factor all of them into the algorithm, but thats still very much work in progress. The 25°C ideal temperature may be a little too high for me, but at that rules out SI levels much above 75 across the Mediterranean in the summer.
A map of air frosts, ground frosts and ice days in the meteorological winter of 2022-23. Remarkably there were more air frosts at Benson in Oxfordshire than there were at Aviemore in the Highlands. I should make an effort to compare these results with a 30 year average but I don’t have the time to compile the stats for each station at the moment. Don’t forget to click an image to enlarge it. Here for completeness is the thermograph for Benson to prove just what a cold hole it is.
