Correlating Summer temperature, rainfall and sunshine in the UK

A while I go I looked into a summer index for the UK, this gave me the idea of producing a couple of charts that correlated mean maximum temperature for the summer [JJA] against rainfall and temperature.  And as you can see from the two charts below it gives a very quick and easy way to spot the warm and sunny years against the cold and wet. Instead of using my old favourite of Daily Central England Temperatures [CET] and England and Wales Rainfall [EWP], I’ve used instead the historic regional data series from the Met Office that extends back to 1910 for temperature and rainfall, and from 1929 for sunshine. The regional monthly and seasonal values are of course calculated from gridded values and that’s the reason they are so short. The application can display charts for any region but for now the entire UK is what is of interest to me. It maybe that a linear trend line is not the best way of testing any correlation, and there must be a way of doing a three-way correlation, but for now this will have to do! Click the image to enlarge it as usual.

UKMO Climate series UK Summer Sunshine, Rainfall & Temperatures

Summer 1954 – worst in living memory?

In a recent article about the Summer Index  in Central England, summer 1954 came in at the bottom of the table with the worst possible scores for temperature, rainfall and sunshine since at least 1929. In researching for this article by looking back in the online archives of the Royal Meteorological Society, I did find that 1931, 1922 (mental note to find out why the summer of 1922 was so cold) and 1912 all rivalled 1954 as the worst summer on record, but I have a special affection for 1954 because it was in the summer of that year I was born.  Here are the headlines for the months of the extended summer of 1954 that I’ve grabbed from the Monthly Weather Report for each month that the Met Office make available online (they are Crown copyright – so I hope they don’t mind).

  • 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.

To begin with I thought that I would just look back at the circulation patterns of the summer using the reanalysis MSLP data from NOAA, so the next three charts are the mean pressure for each meteorological month of the summer, followed by three more anomaly charts for June, July and August.  As you can see from the first three charts the summer was dominated by a west or northwesterly flow, which during July was quite strong.

Mean Sea Level Pressure 1 Jun - 30 Jun 1954

Mean Sea Level Pressure 1 Jun – 30 Jun 1954

Mean Sea Level Pressure 1 Jul - 31 Jul 1954

Mean Sea Level Pressure 1 Jul – 31 Jul 1954

Mean Sea Level Pressure 1 Aug - 31 Aug 1954

Mean Sea Level Pressure 1 Aug – 31 Aug 1954

The monthly anomaly charts for each month all show an anomalous low to the northeast or east of the British Isles, with mean pressure between -5 and -9 hPa lower than the monthly long-term average.

Mean Sea Level Pressure Anomalies 1 Jun - 30 Jun 1954

Mean Sea Level Pressure Anomalies 1 Jun – 30 Jun 1954

Mean Sea Level Pressure Anomalies 1 Jul - 31 Jul 1954

Mean Sea Level Pressure Anomalies 1 Jul – 31 Jul 1954

Mean Sea Level Pressure Anomalies 1 Aug - 31 Aug 1954

Mean Sea Level Pressure Anomalies 1 Aug – 31 Aug 1954

And here are the 1200 UTC surface temperature anomalies also from reanalysis data which show how cool, if not cold it was, not just across the British Isles but also the near continent through each of the summer months.

Air Temperature Anomalies 01 Jun to 30 Jun 1954

Air Temperature Anomalies 01 Jun to 30 Jun 1954

Air Temperature Anomalies 01 Jul to 31 Jul 1954

Air Temperature Anomalies 01 Jul to 31 Jul 1954

Air Temperature Anomalies 01 Aug to 31 Aug 1954

Air Temperature Anomalies 01 Aug to 31 Aug 1954

Here for good measure are the mean temperature anomalies for the entire summer courtesy of the Met Office.

1954_14_MeanTemp_Anomaly_1961-1990

Summer 1954 – mean temperature anomalies

The British Isles were in quite deep (for the time of year) cold air for long periods during the summer of 1954. I count 49 of the 92 days of that summer when sub 552 dm partial thicknesses (the green blobs) covered all or some part of the British Isles.

North Atlantic MSLP & 500 gh [WZ] Summer [JJA] 1954

North Atlantic MSLP & 500 gh [WZ] Summer [JJA] 1954 (courtesy of Wetterzentrale)

Of all the information and graphics that I have packed into this article, none of them conveys as much as the next graphic just how exceptional the Summer of 1954 was. It’s a chart of daily Central England Temperatures [CET] and anomalies for the entire Summer. The fifth chart from the top displays cold or warm spells that have lasted for four days or longer and were +/- 2°C  above the long-term average for that day, and as you can see in the entire summer there were only three warm spells, and all of them spells of high night-time minima rather than day time maxima.

Daily CET Summer [JJA] 1954

Daily CET Summer [JJA] 1954

Here is a list of the coldest summers in the CET monthly series since 1659. Although 1954 was cold, coming in at the 17th coldest with a mean anomaly of -1.19°C, there have been colder summers including that of 1922 with an anomaly of -1.72°C.

Coldest Summers (1659-2016)

Coldest Summers (1659-2016)

And finally a look at the daily rainfall totals for England and Wales from the UKP data series that are maintained and made available by the wonderful Met Office yet again. It was a wet summer and according to the figures it was over 40% wetter than average. It looked very wet from the 5th of June for at least ten days or so, with wet spells again in late July and again through the first three weeks of August.

HadUKP England & Wales 1 June 1954 - 31 August 1954

HadUKP England & Wales 1 June 1954 – 31 August 1954

In writing this article I’ve finally come to realise that I have developed an amazing set of applications to display climate data, but charts, tables and maps aren’t the be all and end all of what makes an interesting article about past weather events. To glue all those disparate images together you need meaningful textual information about whatever event your article is about, and if that event happened over sixty years ago like this one did, when you were either perhaps too young or not even born, then you can’t always write about it with the benefit of first hand experience.

Summer days in Central England

IMG_9414

I reckon that a temperature of 26.7°C or 80°F is the threshold for a summer day in Central England. If you set the threshold any higher the number of occurrences drops off quite a bit. I analysed the data back to 1878 when the daily series started pushing out both maximum and minimum temperatures, and as you can see from the chart below there has been a 43.1% increase in the annual number of days with a maxima equal or higher than 26.7°C since 1878.

Daily Central England Temperature

Daily Central England Temperature – annual number of days with maxima >=26.7°C

The table below shows the results from three different thresholds (25, 26.7 & 28°C). The table is sorted and ranked on the 26.7°C column, and the year 1995 with 24 days with maximum temperatures of 80°F or higher tops the results, quickly followed by 1976 the year with the great summer.

Daily Central England Temperature 1 Jan 1878 - 18 Jul 2016

Daily Central England Temperatures – annual maximum temperatures 1878 – 2016

And here are the results grouped by decade:

Daily Central England Temperature 1 Jan 1878 - 19 Jul 2016

Daily Central England Temperature – maximum temperatures by decade 1878 – 2016

Of course some years are worst than others, 2012 had no days in Central England with a maxima above 80°F, so did 2012, and the very bad summer of 1954 (not in this list) only had one day with a temperature above 25.0°C!

Daily Central England Temperatures 1 Jan 1878 - 18 Jul 2016

Daily Central England Temperatures 1 Jan 1878 – 18 Jul 2016

 

Finally, here is a chart of the number of days with a slightly lower threshold of 25.0°C, which as you can see from the chart shows an even greater 59% increase in the annual number of such days since 1878.

Daily Central England Temperature

Daily Central England Temperature – annual number of days with maxima >=25°C

In conclusion the CET is showing a strong increase in warm or very warm days in the series back to 1878, the increase is of course erratic as you would expect, but the trend over the last 138 years is upwards, and that means whether we like it or there will be an increasing number of warm or very warms days in Central England in the years to come.