by Philip Eden

There has always been an impression that certain types of weather recur at certain times of the year – indeed, the idea is enshrined in ancient country lore which contains myriad sayings and proverbs which tie climatic characteristics to the calendar.

But most thinking people would regard as preposterous the notion that the atmosphere can remember how it behaved on a particular date in previous years so that it can do the same this year. Put as starkly as that, the idea is certainly irrational and unscientific. But a gargantuan heap of statistical work over the last century and half has identified some significant tendencies to unusual weather at particular times of the year. These seasonal tendencies are called ‘singularities’ – a word coined by the German climatologist, A.Schmauss, in 1938.

Work on singularities can be said to date back to Alexander Buchan’s analysis of Edinburgh temperatures in 1869 in which he identified times of the year which were regularly warmer or colder than would be expected from the smoothed annual curve of mean temperature. These famously became known as “Buchan’s cold and warm periodsö and were widely quoted out of context during the last century. More detailed and extensive work was conducted on the continent – notably in Germany, the Netherlands, Austria and Sweden – during the early-1900s, and the subject was taken up in the UK Meteorological Office by C.E.P.Brooks, J.E.Belasco, and H.H. Lamb from the 1930s onwards.

Rigorous statistical techniques were applied to daily sea-level pressure patterns over Europe and the north Atlantic over a period of 60 years. The end result was that several key periods were identified throughout the year when these synoptic patterns deviated markedly from the normal seasonal progression. The events certainly did not happen every year, nor were any exact dates set in stone, but more than 20 singularities which occurred in more than half the years of the analysis were detected in the British climate:

Event	Avg. Start	Avg. End	Peak	Frequency %
Early-Jan storms	5 Jan	17 Jan	8 Jan	86
Mid-Jan settled	18 Jan	24 Jan	21 Jan	86
Late-Jan storms	24 Jan	1 Feb	31 Jan	84
Early-Feb settled	8 Feb	16 Feb	13 Feb	56
Early-Mar storms	26 Feb	9 Mar	1 Mar	88
Mid-Mar settled	12 Mar	19 Mar	14 Mar	52
Late-Mar storms	24 Mar	31 Mar	28 Mar	67
Mid-Apr storms	10 Apr	15 Apr	14 Apr	71
Late-Apr rains	23 Apr	26 Apr	25 Apr	52
June monsoon	1 Jun	21 Jun	16 Jun	77
July heatwave	10 Jul	24 Jul	16 Jul	80
Late-Aug winds	20 Aug	30 Aug	28 Aug	67
Early-Sep warmth	1 Sep	17 Sep	10 Sep	82
Mid-Sep storms	17 Sep	24 Sep	20 Sep	60
Old Wives’ Summer	24 Sep	4 Oct	29 Sep	64
Early-Oct storms	5 Oct	12 Oct	9 Oct	67
St Luke’s Summer	16 Oct	20 Oct	19 Oct	67
Mid-autumn storms	24 Oct	13 Nov	29 Oct	100
St Martin’s Summer	15 Nov	21 Nov	18 Nov	66
Early-Dec storms	24 Nov	14 Dec	9 Dec	98
Mid-Dec settled	18 Dec	24 Dec	21 Dec	56
Christmas storm	25 Dec	1 Jan	28 Dec	84

After a further sixty years these singularities are still identifiable on many occasions. Even in this era of high-tech weather forecasting, the list can still come in useful from time time: for example, when medium-range ensemble forecasts point in two contrasting directions the real atmosphere is most likely to follow the route closest to any relevant singularity.

© Philip Eden