Possibly the warmest May on record?

I have read reports that this month will end up being the warmest May on record thanks to a heat wave in the last 10 days of the month. Going by the latest provisional values of the Central England Temperature [CET] series, so far this month (up until the 20th) that looks a total impossibility. A quick bit of calculation to see just how hot the last 11 days of the month would have to be to beat May 1833 reveals that the daily mean would have to exceed 20.1°C for every remaining day of the month. The people who are making these predictions obviously didn’t realise just how exceptionally warm May 1833 was, +4.64°C above the long-term average. Currently May 2016 is tracking just inside the top twenty warmest at #19, with a mean anomaly of +1.97°C, which in itself is very high. Even if the short cold spell between the 14-16th hadn’t occurred it still wouldn’t have been anywhere close to beating 1833.

Daily Central England Temperature Warmest start to a May 1772 - 2016
Daily Central England Temperature Warmest start to a May 1772 – 2016

Remember you can keep an eye on the latest CET values in these special static pages dedicated to them.

Ice Saints

As Wikipedia points out – Ice Saints is a name given to St. Mamertus (or, in some countries, St. Boniface of Tarsus), St. Pancras, and St. Servatius in Austrian, Belgian, Croatian, Czech, Dutch, French, German, Hungarian, North-Italian, Polish, Slovene and Swiss folklore. They are so named because their feast days fall on the days of May 11, May 12, and May 13 respectively, known as the “black-thorn winter”.

The period from May 12 to May 15 was noted to bring a brief spell of colder weather in many years, including the last nightly frosts of the spring in the Northern Hemisphere under the Julian Calendar. The introduction of the Gregorian Calendar in 1582 involved skipping 10 days in the calendar, so that the equivalent days from the climatic point of view became May 22–25.

Ignoring the spanner in the works that the change of calendar introduces – I decided to rework the code in my Central England Temperature [CET] application just to see if there was any evidence in the CET series to justify this singularity. Below is the list since 1970 (let me know if you want more), and as you can see Ice Saints do happen and more often than you might think, but by now the effort in just writing the extraction and plotting routines had got to me. It’s obvious to me from the scatter graph that you can’t say for certain that this singularity does exist and can be relied on for those specific dates in May, certainly H.H.Lamb didn’t think a lot of it in his book “The English Climate”, even though it does coincide with one of Buchan’s infamous cold spells, but it does coincide nicely with what Lamb calls the “Spring Northerlies” (16 April to 20th May).

The way I investigate it was to look at three five-day periods 6-10 May, 11-15 May and the 16-20 May. I then calculated the anomaly of each of these three pentads, calling them A, B and C, and then compared the difference between A and B and then B and C for each year since 1772.

Daily Central England Temperature Ice Saints Singularity Comparison 1772-2016
Daily Central England Temperature Ice Saints Singularity Comparison 1772-2016
Daily Central England Temperature SubTitle
Daily Central England Temperature Ice Saints Singularity Comparison 1772-2016

The most striking Ice Saints of recent years in the CET series was in 2010 and here are the analysis charts for that time. As you can see a northerly outbreak very similar to the one occurring this year (2016) was responsible. This period is after all when the peak frequency of N’ly types in the Lamb Weather Type [LWT] series occur. It certainly put paid to the unusual early warm spell that we had been experiencing up until the 13th, and ruined any real chance of an Ice Saints for 2016.

8 May -21 May 2010 (courtesy of the Met Office)
8 May -21 May 2010 (courtesy of the Met Office)
Daily CET Spring 2010
Daily CET Spring 2010

Probably the most severe examples of Ice Saints since 1772 occurred in 1830 and 1816 as you can see in the scatter plot chart.

CET Spring 1830
CET Spring 1830
CET Spring 1816
CET Spring 1816

The eagle-eyed amongst you may have noticed just a very slight cooling in the daily CET graphs (above) of the 1961-1990 long-term average (the green filled area series) between the 13th and 18th of May.

Warmest 8th of May since 1878

Warmest Central England Temperature for the 8th of May
Warmest Central England Temperature for the 8th of May

Provisionally yesterday – Sunday the 8th of May 2016 – was the warmest 8th of May in Central England since at least 1878. The maximum temperature anomaly was +10°C warmer than the 1961-1990 long-term average for that day and was a full 2°C warmer than the previous warmest that occurred in 2008. The mean temperature was the highest since at least 1772 at 18.0°C and exceeded the previous highest mean of 1867 by 1.1°C. Quite an exceptionally warm day for early May.

03772 London Heathrow - United Kingdom 24 AMSL 2 May-8 May 2016
03772 London Heathrow – United Kingdom 24 AMSL 2 May-8 May 2016