EXTREMES//MAXIMUM TEMPERATURES

Maximum Temperatures

Overview

In 1875 the Royal Meteorological Society organised a network of Climatological Weather Stations, regularly inspected and using verified thermometers. The instruments were exposed in the Standard Stevenson Screen, a procedure also encouraged by the Scottish Meteorological Society and the British Meteorological Office (e.g. for synoptic stations). Summaries of observations from these standard and representative sites were subsequently published in the Meteorological Record of the Royal Meteorological Society, the Journal of the Scottish Meteorological Society, and the Monthly Weather Report of the Meteorological Office. Since 1875 the highest temperature of the year in Britain has been registered as early as 14th May 1965 and as late as 27th September 1895 (for some details, see Journal of Meteorology, 9(87), 69-72). A table of Britain's highest recorded temperatures for each day of the year was originally published in Journal of Meteorology, 9(90), 169-176; a revised list and associated article was published in Weather, 55, pp 298-315. A further revision, plus a full list of UK county extremes (updating the list published in Weather, 48, 282-291), was published as an appendix to the TORRO 40th anniversary book Extreme Weather in 2015, and is available here.

The highest mid-winter temperatures are the result of a 'Fohn', where very mild air advected on a south or south-westerly airstream is warmed (by adiabatic compression) on descent from mountain ranges. Outstanding examples include the temperatures of 18.7°C registered in northwest Scotland in December 2019 and 18.3°C recorded in North Wales in January 1958 and January 1971. East Devon, the Welsh borders, North-west and North-east Scotland have also experienced temperatures above 16°C in December or January in similar circumstances.

During early spring the occurrence of very high temperatures still depends on the advection of air from a warm source. This is now most effective across Eastern parts of England when a warm southerly airstream arrives across the relatively narrow eastern English Channel. The latter is also the most favourable situation for high autumn temperatures when sea temperatures are considerably higher but the fading power of the sun ensures that temperatures decline steadily once a supply of warm air has been cut off. North-facing resorts along the East coast of England like Cromer and Whitby (both backed by hills to the South) feature in several of the highest recorded spring and autumn temperatures (e.g. 23.3°C at Cromer on 9 March 1948). This demonstrates how cooling (or, in Spring, chilling!) sea breezes are inhibited by a steady offshore prevailing wind.

Between April and September the direct advection of a very warm air mass is not the only origin of high temperatures; progressively rising temperatures occur during any spells of calm and sunny anticyclonic weather (as in late June 2018) when the highest values are often recorded in Central England, e.g. in the Thames, Severn-Avon and Trent Valleys. The occurrence of numerous extreme Spring, Summer and Autumn maxima in the London area may reflect the "urban effect" but also the fact that the capital is favourably sheltered to the south by the North Downs. While relatively brief incursions of very hot air have produced some of the UK’s highest temperatures, including the current record of 40.3°C at Coningsby in July 2022, prolonged heatwaves and widespread high maxima are most likely when a very hot air mass stagnates over the country, such as in 1976 and 2003. The record length hot spell of late June to early July 1976 was preceded by a long period of dry, warm weather. The consequent lack of ground moisture resulted in a high proportion of the sun's energy being utilised to heat the air, rather than being used for evaporation.

As during Spring and Autumn very high summer temperatures can be recorded even along the coast when an appreciable offshore gradient wind hinders the development of a sea breeze (as on 18-19 July 2022). The development of these refreshing coastal breezes is also suppressed by the atmosphere stability associated with anticyclones which inhibits the ascent (convection) of hot air inland. In more favourable unstable conditions a `sea breeze' blows inland to replace these ascending currents of warm air. Temperatures above 32°C were recorded at numerous coastal locations during the predominantly anticyclonic heat-waves of June-July 1976 and August 1990. An unusual British `heat-wave' occurred way back on 6th August 1910 when 28°C was registered in the Shetland Isles, while nowhere elsewhere in Britain exceeded 20°C. The extraordinary weather situation responsible is described in Journal of Meteorology, 9(91), 211-213.

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Highest recorded temperatures for each month of the year, 1875 to 2020

Month	°C	°F	Location	Region	Date
January	18.3	65.0	Aber	Gwynedd	27 January 1958
	18.3	65.0	Aber	Gwynedd	10 January 1971
	18.3	65.0	Aboyne	Aberdeenshire	26 January 2003
	18.2	64.8	Llandudno	Gwynedd	10 January 1971
February	21.2	70.2	Kew Gardens	London	26 February 2019
	20.8	69.4	Northolt	London	26 February 2019
	20.8	69.4	Porthmadog	Gwynedd	26 February 2019
	20.6	69.1	Teddington	London	25 February 2019
	20.6	69.1	Trawsgoed	Ceredigion	25 February 2019
March	25.6	78.0	Mepal	Cambridgeshire	29 March 1968
	25.0*	77.0*	Wakefield	West Yorkshire	29 March 1929
	25.0*	77.0*	Wakefield	West Yorkshire	29 March 1965
	25.0	77.0	Cromer	Norfolk	29 March 1968
	25.0	77.0	Santon Downham	Norfolk	29 March 1968
	24.9	76.8	East Dereham	Norfolk	29 March 1968
April	29.4	85.0	Camden Square	London	16 April 1949
	28.9	84.0	Cambridge	Cambridgeshire	20 April 1893
	28.9	84.0	Kensington	London	16 April 1949
	28.9	84.0	Wealdstone	Greenwich	16 April 1949
May	32.8	91.0	Camden Square	London	22 May 1922
	32.8	91.0	Horsham	West Sussex	29 May 1944
	32.8	91.0	Tunbridge Wells	Kent	29 May 1944
	32.8	91.0	Camden Square	London	29 May 1944
	32.8	91.0	Regents Park	London	29 May 1944
June	35.6	96.1	Southampton, Mayflower Park	Hampshire	28 June 1976
	35.6	96.1	Camden Square	London	29 June 1957
	35.5	95.9	Southampton, Mayflower Park	Hampshire	27 June 1976
	35.4	95.7	North Heath	West Sussex	26 June 1976
	35.4	95.7	East Dereham	Norfolk	26 June 1976
July	40.3	104.5	Coningsby	Lincolnshire	19 July 2022
	40.2	104.4	Pitsford	Northamptonshire	19 July 2022
	40.2	104.4	St James's Park	London	19 July 2022
	40.2	104.4	Heathrow	London	19 July 2022
	40.1	104.2	Gringley on the Hill	Nottinghamshire	19 July 2022
	40.1	104.2	Kew Gardens	London	19 July 2022
	40.0	104.0	Cranwell	Lincolnshire	19 July 2022
	40.0	104.0	Northolt	London	19 July 2022
August	38.5*	101.3*	Faversham	Kent	10 August 2003
	38.1	100.6	Kew Gardens	London	10 August 2003
	37.9	100.2	Heathrow	London	10 August 2003
	37.9	100.2	Aldenham	Hertfordshire	10 August 2003
September	35.6	96.0	Bawtry	South Yorkshire	2 September 1906
	35.0	95.0	New Malden	London	1 September 1906
	35.0	95.0	Maidenhead	Berkshire	1 September 1906
	35.0	95.0	Colly Weston	Northamptonshire	1 September 1906
	35.0	95.0	Barnet	London	2 September 1906
	34.8	94.6	Epsom	Surrey	2 September 1906
	34.8	94.6	Old Southgate	London	2 September 1906
	34.6	94.2	Raunds	Northamptonshire	8 September 1911
October	29.9	85.8	Gravesend	Kent	1 October 2011
	29.4	84.9	March	Cambridgeshire	1 October 1985
	29.4	84.9	Charlwood	Surrey	1 October 2011
	29.3	84.7	Santon Downham	Suffolk	2 October 2011
	29.3	84.7	Coningsby	Lincolnshire	2 October 2011
	28.9	84.0	Whitby	North Yorkshire	1 October 1908
	28.9	84.0	Kensington Palace	London	5 October 1921
	28.9	84.0	Kensington Palace	London	6 October 1921
	28.9	84.0	St James' Park	London	6 October 1921
	28.9	84.0	Hampstead	London	6 October 1921
November	22.4	72.3	Trawsgoed	Ceredigion	1 November 2015
	22.3	72.1	Trawsgoed	Ceredigion	2 November 2015
	21.7	71.0	Prestatyn	Clwyd	4 November 1946
	21.1	71.0	Cambridge	Cambridgeshire	5 November 1938
	21.1	71.0	Chelmsford	Essex	5 November 1938
	21.1	71.0	Mildenhall	Suffolk	5 November 1938
	21.1	71.0	Clacton	Essex	5 November 1938
	21.1	71.0	Tottenham	London	5 November 1938
	21.1	71.0	Halstead	Essex	5 November 1938
December	18.7	65.7	Achfary	Sutherland	28 December 2019
	18.3	65.0	Achnashellach	Highland	2 December 1948
	18.0	64.4	Aber	Gwynedd	18 December 1972
	17.8	64.0	Aber	Gwynedd	17 December 1972
	17.7	63.9	Cape Wrath	Highland	18 December 1972
	17.7	63.9	Penkridge	Staffordshire	11 December 1994

Note: Values qualified by an * are either (a) from rather sheltered sites or (b) more than 2°C above adjacent stations.