CET

The Central England Temperature [CET] record is a meteorological dataset originally published by Professor Gordon Manley in 1953 and subsequently extended and updated in 1974, following many decades of painstaking work. The monthly mean surface air temperatures, for the Midlands region of England, are given in degrees Celsius from the year 1659 to the present.

This record represents the longest series of monthly temperature observations in existence. It is a valuable dataset for meteorologists and climate scientists. It is monthly from 1659, and a daily version has been produced from 1772. The monthly means from November 1722 onwards are given to a precision of 0.1 °C. The earliest years of the series, from 1659 to October 1722 inclusive, for the most part only have monthly means given to the nearest degree or half a degree, though there is a small ‘window’ of 0.1 degree precision from 1699 to 1706 inclusive. This reflects the number, accuracy, reliability and geographical spread of the temperature records that were available for the years in question (intro courtesy of Wikipedia).



2017 now third warmest year to date

Figure 1

In Central England, the latest provisional figures for June show that 2017 is the joint third warmest start to a year (1st of January to the 22nd of June) since 1772. It’s very tight at the top but 2007 is still clear at the top, but that will gradually change because the second half of 2007 was much cooler than the first half of that year.

Figure 2

I’ve been watching 2017 climb slowly up the league table since March, but I think that this maybe as high as it gets, at least for a while, in light of the very much cooler conditions forecast for the coming week in the latest run of the GFS model (fig 3).

Figure 3

2017 in Central England – currently joint 4th warmest

2017, continues to move a little higher up the league table of warmest years to date (the 1st Jan to the 18th June), it’s now joint 4th and is within striking distance of both 1990 (0.02°C higher) and 2014 (0.15°C higher), and the way this current hot spell is going it could will go clear as the second warmest start to any year since 2007 before the week is out, in the daily mean temperature record that started in 1772. This is of course based on provisional values for this month from the Met Office.

Figure 1 – Data courtesy of the Met Office

 

Another way of looking at temperatures in Central England

Figure 1 – Data courtesy of the Met Office

Conventionally the above chart (fig 1) is how we have always thought is the best way to display the vagaries of the CET series; by plotting a fixed yearly bar chart, of either mean CET temperature or anomalies; of course we could add an accompanying table, sorted and ranked to show the warmest years (fig 2).

Figure 2 – Data courtesy of the Met Office

Another way of getting a measure of just how warm or a cold it’s been over the years, is to plot a chart of 365 day rolling mean anomalies (fig 3), this gets round the problem of only looking at a single ‘annual’ temperature, that’s fixed to the period between the 1st of January and 31st of December. As you can see from the graph, both higher and lower temperatures occur outside these fixed ‘annual’ periods, and the time period between the 6th of June 2006 and the 5th of June 2007 is a case in point. That particular 365 day period produced a mean anomaly of +2.15°C, the highest in the CET series since 1878, and probably since 1659, even though statistically the warmest year occurred seven years later in 2014, with a calendar year mean anomaly of +1.44°C, which is significantly over 0.7°C lower.

Figure 3 – Data courtesy of the Met Office

At the moment 2017, as of the 1st of June, has a 365 day mean anomaly of +1.23°C, which is a long way short of either the warmest calendar year, or the warmest 365 day period. But if we compare the first five months of the year, as I’ve done in the table below (fig 4), you will see that 2017 is sixth warmest, a little behind both 2007 and 2014.  But as the year progresses, the value and ranking for 2007 will fall, because the year gradually cooled. But we already know that 2014 is the warmest calendar year in the series, and this one will be the one to beat. With the gap at the moment between them of 0.2°C, 2017 has it’s worked cut out for it, if it’s going to catch it, in what’s left of this year.

Figure 4 – Data courtesy of the Met Office

 

Spring 2017 warmest on record in Central England

Figure 1

It may not have been the warmest May on record, but with the help of a very mild March (ranked #3), Spring 2017 was the warmest since at least 1659 in Central England, with a mean temperature of 10.25°C, which makes the anomaly +2.01°C above the 1961-1990 long-term average. Of course, we are talking here of meteorological seasons MAM, which as you know I’m no great fan of, but what the hell. It was a very closely fought thing though, because 2017 only just pipped 2011 into second place by 0.03°C (fig 3).

Figure 2

Figure 3

 

 

 

Warmest May since 2008 in Central England

Figure 1

It’s been the warmest May since 2008 in Central England, not what you’d call a particularly earth shattering headline is it, but that’s how it panned out. In the ranking back to 1659, the +2.05°C mean anomaly (calculated with respect to the 1961-1990 long-term averages), makes it around the 15th warmest. Since 1910, the year that the Met Office choose to start their climate records from, its seventh in the rankings. The month set a new highest maximum for CET on the 26th, and also two highest minimums on the 16th and 27th.

Summers in Central England since 1659

Figure 1

It’s quite a number of years since we have had a really warm Summer [JJA]. The last very warm one was the summer of 2006 which ranked #4 warmest in the series (fig 2), and before that summer 2003, which ranked joint third warmest, perhaps we’ve been spoiled in recent years, and are taking it for granted that every summer will end up being warm or very warm.

Figure 2

Summers have become slightly warmer during the last 358 years in Central England (fig 3), but not so much that you would notice. They have crept up by around +0.36°C in that time, which is almost exactly +0.01°C a decade, if global warming is having any effect on summers in Central England then it’s being very slow about it.

Figure 3

Steep decline in snowfall since 1931 in Central England

Figure 1 – Original UKP and CET data courtesy of the Met Office.

I reckon that there has been an almost 60% decline in annual snowfall since 1931. This won’t surprise a lot of people, because snow has become something of a scarce commodity in recent Winters, especially the further south that you are. Before I go any further the science behind this article is a bit thin, it’s based on a mix of daily Central England Temperatures [CET] and daily UKP rainfall (central region), but what the hell, you’ve got to start from somewhere, and I don’t think the Met office would have provided me with the required climate data to do this for free.

The biggest fudge factor, and don’t forget that even the most sophisticated and complicated NWP software employ some kind of fudge, is the algorithm that takes a daily maximum and minimum temperature, and decides if there’s any precipitation reported for that day, what likely probability is that it would fall as snow and accumulate. This is obviously easy if the maximum temperature for the day in question was below freezing, but not so easy say if the maximum is +5°C and the minimum is -1°C, so all you can do is give it your best guess. I suppose you could also look up the LWT for that day, and maybe get some kind of idea of what kind of air mass the country is under, but I didn’t go that far, and kept it as simple as possible.

Getting back to the chart (fig 1), you will see that my trusty algorithm has identified the snowiest winter in the last 86 years as being that of 1946-47, so that’s a good start. The second snowiest season it reckons was 1978-79, and having experienced of winters since the early 1960’s in various parts of the country I wouldn’t disagree with that. I guess that the accumulated snowfall for that season, ignoring melting of course, was close to a 100 cm, with 1946-47 producing an accumulation of just over 140 cm. I entitled the first article that I wrote about using daily CET and UKP to estimate a snow depth; ‘Central England Snowfall’; in fact it’s probably more appropriate to imagine the value as an index rather than a specific depth of snow. There have been some years with no snowfall when the algorithm couldn’t detect any snow, these were for the years 1988-89, 2013-14 and 2016-17, perhaps the code I calculate the daily probabilities requires a bit of tweaking, but then again, the last snow that I can remember settling down here in our part of Devon, was way back in 2010.

I did the original work for the application, which I call Central England Snowfall, about ten years ago now, but after deciding to give the code a bit of a spring clean today, I thought that I’d write an article around it. It’s a bit of fun because the science that I use could be regarded as suspect, but as far as I know, there are no long-term graphs available on the internet for annual snowfall totals for any climate station in the UK. If you do find one, or perhaps know of a graph than spans 60 years or more please let me know, because I would be very interested to see it, and would certainly include it in this article. I do have some evidence though, in the shape of daily climate records courtesy of Alistair McClean, Curator of Natural Science at the Weston Park Museum in Sheffield, for the period 1950-2010, which luckily includes daily values of fresh snow and snow depth. As you can see in this shorter period (fig 2), annual totals on the linear trend have also declined, by almost 40% in the last sixty years. The graphs are quite similar, even the estimate of snowfall that I make for the winter of 1978-79 are reasonably close (actual 116 cm estimated 98 cm). Having experienced that winter firsthand in the higher suburbs of that city though, I would say that the reported values maybe rather on the low side.

Figure 2 – Data courtesy of Weston Park Museum, Sheffield

It’s a great shame that the Met Office stopped producing the Snow Survey of Great Britain in 1991, if that information could be digitised and collated it would make a wonderful climate resource for snowfall in the UK. Finally, I would just like to give a special mention to the website of Dr Richard Wild and is thesis ‘Spatial and Temporal Analysis of Heavy Snowfalls across Great Britain between the years 1861-1999‘, a fascinating read for the snow lovers amongst us.

11th mildest start to a year since 1772

Figure 1 – Data courtesy of the Met Office

Now that we’re 136 days into the year 2017, I thought that it was about time I looked to see just how this year was shaping up as regards temperatures in Central England. And as you can see from the table (fig 1), this year is already exceptionally mild, with a mean CET so far this year of 7.47°C which is +1.54°C above the 1961-1990 long-term average. This makes it currently the eleventh mildest start to a year since 1772, but as you can see many of the mildest years in the top 12 have also occurred in recent years.

April warmth cancelled out by late cold spell

The early April warmth was cancelled out a little by the late cold spell in Central England, which although lasted no more than 5 days, did manage to limit the mean temperature to just 8.9°C for the month. The final mean anomaly, which had been running at almost +3°C earlier in the month, ended up at +0.97°C.  It was the warmth of the days that help produce the +0.97°C anomaly, the mean maximum anomaly was +1.57°C, whilst the mean minimum anomaly was only +0.39°C. Eleven of the last 12 months have been warmer than average. I still calculate all my anomalies with respect to the 1961-1990 long-term average.

Figure 1 – Data courtesy of the Met Office

One notable extreme maximum record was set during the month on Sunday the 9th, which had a maximum of 21.4°C which was +10.5°C above the average for that day.

Figure 2 – Data courtesy of the Met Office

Late April cold spells and the Easter Snowstorm of 1908

Figure 1 – Lymington High Street – April 25th 1908 (courtesy of lymington.org)

Easter in 1908 fell late, so the snow that fell over much of southern England must have come as a big surprise on the Easter Sunday on the 19th of April (fig 1). The following week was intensely cold for late April, and there were periods of heavy snow across much of southern England. In an article in the Met Mag of May 1908, Fred J Brodie said this about the snow at Oxford:

The conditions at Oxford are interesting in a special degree on account of the length of the meteorological records at the Radcliffe Observatory which run from 1853. The depth of snow there was 17 inches, and the only instance of a greater amount being recorded at any time of year was on February 13th and 14th, 1888, when 24 inches of undrifted snow was measured.

I love the comment that Fred went onto make a few lines further on…

The practice of comparing, for the purpose of record making, observations made in two different localities is not to
be commended…

He of course is completely right in what he says, but he must be spinning in his grave these days, on the goings on in the early 21st century with extreme temperature records I would have thought, because no one, and that includes myself seems to give a hoot these days about comparing extremes from weather stations without knowing thinking much about their actual location. You can find an article about the events of April 1908 on the Weather Outlook forum, which includes details of snow depths recorded at the time, plus a lot of other information and photographs about the blizzard. The Weather Magazine of December 1981 also had an article about April 1908 in which it linked it to the April of 1981 and said:

The marked similarity of the graphs for 1908 and 1981, especially in the second half of each, is confirmed by a correlation coefficient of 0.93 for the last 15 days of the month. For the full month the correlation coefficient is 0.65. The weather of late April was remarkably similar in these years.

Since 1981, the daily CET series may well have undergone some slight modifications, but there is most definitely a cold spell that occurred during at the second half of each month, the minimum CET in 1908 was a couple of degrees colder than it was in 1981 though, and those on the 24th and 25th still hold the record for lowest minimums on those two days (blue stars). Personally I only see a broad similarity between the two, I’ll have to spend some time and write some code to generate a correlation coefficients between these two months and see what I come up with. If you look closely at the graph of CET (fig 2), you’ll notice that in just over a week, maximum anomalies rose from around -8°C to +8°C. The resultant rapid thawing of lying snow from the week-long cold spell lead to great flooding in places along rivers in the southeast especially the Thames, and the Great Ouse at Buckingham.

Figure 2

Synoptically, the 25th of April in both 1908 and 1981 were slightly similar in that they were both cyclonic in nature.

Figure 3 – Courtesy of NCEP/NOAA reanalysis

But up aloft in the atmosphere the cold air of 1908 was much deeper than it was in 1981 (figs 4 & 5).

It seems cold outbreaks towards the end of April are not at all uncommon, I’ve just picked on probably two of the more extreme events. Next week promises its own cold outbreak (fig 6), but synoptically, if the GFS model is correct, it will be more of a cold northerly rather than cyclonic as it was either in 1908 or 1981.

Figure 6 – Courtesy of OGIMET