April can be a month when you get a taste of spring, summer and winter, sometimes all in one day, so the latest forecast chart for next Wednesday (the 12th of April) from the GFS will come as no surprise (fig 1). A cold northerly with 1000-500 hPa partial thicknesses below 522 dam across the North of Scotland for a time, and if this forecast is right, then it will be the second time this year that one of Alexander Buchan’s singularities has been correct, the first time was noticeable in the CET series between the 6th and 12th of February. This cyclonic interlude is forecast to be short-lived, as high pressure returns for the Easter weekend in the south.
Despite a relatively cold spell from the 5th to the 12th (fig 1), which almost coincided with Alexander Buchan’s first cold spell singularity, February ended up a very mild month, with a mean temperatures in Central England of 6.1°C, which was +2.34°C above the 1961-1990 long-term average. There was an all time maximum set on the 20th for 14.1°C, which was the warmest day in Central England since at least 1878, I did cause a bit of a stir on the day when the temperature reached 18.3°C at Northolt and Kew in London.
I make February 2017 was the joint 30th mildest since 1659 (fig 2) in the CET data that I download from the Met Office, hopefully this month I’ve downloaded the latest finalised data unlike last month!
Because so many recent February’s have been mild in recent years, February 2017 was only the mildest since 2014 (fig 3), cold February’s these days, are getting few and far between I’m afraid.
October 2016 has been the third most anticyclonic October since 1871. Not a lot of people know that. Here’s a table of the monthly analysis ranked on highest anticyclonicity using the Objective Lamb Weather Type [LWT] data series maintained by the Climate Research Unit at the University of East Anglia.
And here’s a more detailed breakdown of the daily LWT values for October 2016.
The more eagled eyed amongst you may have noticed that I have highlighted October 1946, 1962 & 1978 in the first table in green. These of course are October’s that preceded the most severe winters since the second World War, namely 1946/47, 1962/63 and 1978/79. In fact the more I look at the list the more severe winters I see, for example 1879/80, 1887/88 and 1985/86 and the bitter cold spell in the January of that winter. Having said that 2007 was the joint 2nd most anticyclonic October and the following winter was super mild, so forget all that twaddle!
I have just done a little research into the ‘return of the westerlies‘ using the objective Lamb Weather Types [LWT] that are available to freely download from the Climate Research Unit [CRU] at the University of East Anglia [UEA]. The ‘return of the westerlies’ was a phrase coined by Hubert Lamb to describe the onset of the ‘European summer monsoon‘ a singularity that affected the British Isles and usually occurred between the 18th and 22nd of June each year. Here are the results of the work I’ve done so far on it, in the form of three charts of daily frequency of westerlies through the year, as well as mean pressure, gale index and daily frequency of cyclonic and anticyclonic types.
The top chart shows the westerly flow frequency. This is calculated by adding 0.5 for any SW or NW days, and 1 for any pure westerly type days. I have derived the anticyclonicity and cyclonicity frequencies in a similar way, that is if they are hybrid such as ‘ASW’, I have added 0.5 to anticyclonicity total rather than 1 for a pure anticyclonic day. If that sounds a bit complicated and doesn’t make much sense I can assure you this is how people including Lamb generated statistics from LWT’s in the past. Anyway back to the chart. You will notice that cyclonicity increases from 30 to 38% from the 5th to the 12th of the month in the lower chart, during the third week of June the westerly types increase from around 14 to over 20%, during the same period the mean air pressure falls across the country from a maximum annual mean of almost 1017 to 1015 hPa.
I have looked at my code and double checked the results but I can’t make the figures look as striking as when Lamb seemed to find them back in the 1960’s. Obviously the reason could be all down to me and my programming, but the other reason could be of course is that I’m using the objective data and not the subjective classification he assigned to each day up to his death in 1997. Reading various papers about the differences between the two schemes, its well-known that the objective method does classify fewer westerly types and more southerly types than did the subjective one did. Please feel free to point me to any more recent research on the subject that either agrees or disagrees with what I’ve come up with.
Anyway, we are at that time of year when the westerlies should be returning across the British Isles, and this year they may be running a little bit early, because the process looks to be well under way. This singularity may be weak, and not very well understood, but it still seems to recur in most June’s, and this one looks like it’s going to be no exception.
As Wikipedia points out – Ice Saints is a The 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.
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.
Probably the most severe examples of Ice Saints since 1772 occurred in 1830 and 1816 as you can see in the scatter plot chart.
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.