SOME COMMENTS ON THE UK NATIONAL DAILY MAXIMUM TEMPERATURES DURING 1999

Abstract: Temperature readings taken from the Internet have been used to produce some brief comments on the UK national daily maximum temperatures in 1999. The author hopes to conduct similar studies over the coming years with the aim of seeing if any interesting patterns are apparent.

One aspect of the British weather that has been of considerable interest to this author for some time is the location and value of daily maximum temperatures, particularly when these temperatures are considerably above average. Inspired by Hickcox (1999) and Webb and Meaden (1993, 1997), data available at Roger Brugge's homepage was been used to make some comments and observations about national daily maximum temperatures in 1999.

Some of the data at this site are also available to the public via page 419 of Ceefax (BBC teletext) and are carried in some national newspapers the following day. Any given figure may not necessarily be that which is quoted as the national daily high in the Daily Weather Summary of the UK Meteorological Office though, because some higher temperatures may become apparent at a later date when reports from climatological stations are taken into consideration (Brugge, personal communication). However the author also wishes to demonstrate how information freely available can be used to produce an informative article, so has chosen to use data from Roger Brugge's homepage rather than that from the Daily Weather Summary.

As with all studies of extreme forms of weather, the author is aware that whilst most weather observations are thought to be reliably made, there is a chance that in years to come some of the data used in this study may become disregarded for reasons of data quality control or possibly even invention (Dukes and Eden 1997). For example, Eden (1991) details considerable evidence to cast doubt on a reading made at Gunby (Lincolnshire) during the summer of 1959 which had been quoted in some papers.

Figure 1 shows a day-by-day record of the national daily maximum temperature during 1999, with values taken from Roger Brugge's homepage. It should be pointed out that no information for August 26th and 27th is available from this source.

Graph showing UK maximum temperatures in 1999An initial inspection of Figure 1 shows that the high of 35C, recorded at Mildenhall (Suffolk) on 2 August, was the highest temperature of 1999 whilst the lowest daily maximum temperature was 7C at Penzance (Cornwall) on 9 February. There were nine days in 1999 when temperatures of 30C or more were recorded somewhere in the UK, while on 59 days temperatures reached 25C or more in at least one site. A maximum temperature of 20C or more was recorded somewhere in the UK on 142 days, whilst at the other end of the scale there were only 14 days when temperatures failed to reach 10C nationally.

A more detailed examination of Figure 1 shows that there a was a very mild start to 1999 when temperatures in the first week of January reached the mid teens locally. The high of 16C in London on 6 January was Londonís highest day-time temperature since 1841, whilst on the same day maximum temperatures over the Home Counties as a whole were the highest January readings during the 20th century (Eden 1999a). February 1999 was considerably colder than that of 1998 which, according to Eden (1998), was the equal third warmest in the Central England Temperature Series; the warmest days in February were the 4th and 19th when temperatures reached 15C.

Moving into the spring, Figure 1 shows some brief warmth in mid-March when temperatures exceeded 20C for the first time in 1999 on the 17th, when Shobdon (Herefordshire) reached 21C. Incidentally, the earliest date on record when 20C was recorded occurred on the 2 March in both 1939 and 1977 (Webb and Meaden, 1997). Late March and early April then saw the yearís first prolonged warm spell when three consecutive days with highs over 20C were followed by four consecutive days with maxima in the high teens. The next warm spell came in late April and early May when temperatures exceeded 20C somewhere in the UK for eleven consecutive days, with a reading of 25C at Saunton Sands (Devon) on 3 May being the highlight of this warm spell. The end of spring saw some even higher temperatures, with 27C reached for the first time in 1999 at Southampton (Hampshire) on 29th May (this bout of hot weather was also associated with some severe thundery outbreaks - see Prichard, 1999).

Looking at the summer of 1999, temperatures failed to exceed 27C in June but there were some hotter days in July when temperatures reached or exceeded 27C on seventeen days and 30C on six days. This summer heat peaked between 30 July and 2 August when temperatures reached at least 31C somewhere in the UK on four consecutive days, while highs of 34 and 35C on the 1 and 2 August respectively (recorded at Mildenhall, Suffolk) were the hottest days of 1999. The rest of August was cooler and it was not until September that temperatures in the 30s were reached nationally again.

Days with temperatures above 30C seemed to be a feature of the UKís climate during the latter part of the 19th century and first 30 or so years of the 20th century (Eden 1995), most sensationally in 1906 when Bawtry near Doncaster (South Yorkshire) reached 35.6C on the 2nd - the fifth hottest day on record in the UK. In more recent times September has been largely free of this kind of heat and in fact until September 1999 the last time a high of 30C had been recorded in the UK during that month was 1973. With this in mind the heatwave of the first half of September 1999 was quite spectacular: on the 11th temperatures peaked when highs reached 30C for the first time in that month for 26 years, Gravesend (Kent) ending up with this distinction. Other highlights of this heatwave were that temperatures on ten of the first eleven days in September reached or exceeded 25C somewhere around the UK, whilst on seven of these eleven days temperatures of at least 27C were recorded in at one or more sites. Moving on through the autumn, Figure 1 shows the last time 20C was exceeded nationally in 1999 was on 10 October at Herne Bay (Kent) where temperatures reached 21C. The latest date in the year on which 20C has been recorded was in 1906 on the 23 November (Webb and Meaden, 1997). Temperatures during most of November and all of December failed to exceed 15C (4 November in Eastbourne (East Sussex) being the last occasion this happened); the lowest maximum temperatures during the last two months of 1999 were in the second half of December, a period which during which some observers recorded their lowest December maxima since 1991 (Brugge 1999a).

Table 1 indicates the top ten Ďhot spotsí in 1999. Rather predictably places in the south-west, the south coast, the Channel Islands and Greater London dominate the number of national highs and, as one might expect, there is a certain seasonality as to when some regions registered the highest maximums. For example, every occasion when St. Maryís (Isles of Scilly) was the warmest place nationally was during the winter and almost all the occasions when Guernsey (Channel Islands), Torquay (Devon) or Penzance (Cornwall) was the warmest place in the UK occurred during the autumn or winter. Also, on more than half of the winter days in 1999 either Guernsey, Torquay, Penzance or St. Maryís was the warmest place nationally. Most of the days when London, Herne Bay (Kent), Poole (Dorset) or Lee-on-Solent (Hampshire) recorded the highest maximum temperatures were in spring, summer or autumn, whilst the occasions when Jersey (Channel Islands) and Southampton (Hampshire) were the UKís warmest site were rather more evenly distributed through the four seasons.

Table 1: The ten Ďhotspotsí in 1999.
 
Rank Location Number of National Highs
1 Guernsey 35
2 London* 33
3 Torquay 29
4 Penzance 28
5 Herne Bay 25
6 Poole 23
7 Jersey 15
8 St. Mary's 9
9 Southampton 8
10 Lee-on-Solent 7

*includes readings from Kensington, London Weather Centre, Northolt and Heathrow Airport.

Table 2 shows the record highs month by month over the UK, figures which were obtained from http://www.torro.org.uk and supplemented by Eden (1998), Walton (1999) and Webb (personal communication). The location of the highest month by month maxima in 1999 have been added for comparison and, unlike 1998 when highs on 13 February broke the February record maximum temperature (Eden 1998, Walton 1999, Webb, personal communication), highs in 1999 did not even come close to threatening existing records. However, it should be pointed out that the 35C recorded at Mildenhall (Suffolk) on 2 August was one of the very few times a high of 35C has been recorded in the 1990s; the author believes that this was the highest temperature recorded in the UK since 1990. Meanwhile, the 30C recorded at Gravesend (Kent) on 11th September was the first time temperatures in the UK had reached 30C in that month since 1973 and the highest this late in the year since 1947 (Eden 1999b).

Table 2: Record national highs (month by month) and 1999 national highs (month by month).
 
RECORD HIGHS 1999 HIGHS
Month High (C) Date Location High (C) Date Location
Jan 18.3 27th 1958 & 10th 1971 Aber 16 16th London
Feb 19.7 13th 1998 London 15 4th & 19th Hawarden & Wittering
March 25 29th 1929, 1965 & 1968 Wakfield 21 17th Shobden
April 29.4 16th 1949 London 22 27th, 29th & 30th Dalmally, Charterhall & London
May 32.8 22nd 1922 & 1944 London 27 29th Southampton
June 35.6 28th 1976 & 29th 1957 London & Southampton 27 16th & 26th London (both times)
July 36 27th 1911 Epsom 32 31st Barbourne
Aug 37.1 3rd 1990 Cheltenham 25 2nd Mildenhall
Sept 35.6 2nd 1906 Bawtry 30 11th Gravesend
Oct 29.5 1st 1985 London 21 10th Herne Bay
Nov 21.7 4th 1946 Prestatyn 18 1st Gravesend
Dec 18.3 2nd 1948 Achnashellach 15 1st Thorney Island

Table 3 shows the ten hottest days of 1999, all of which saw temperatures reach at least 30C. Most of these days occurred in July, which was also by far the warmest month in the Central England Temperature series (Brugge 1999b). A further nine days recorded a high of 29C; three of these days were in the first five days of September, five were in July and the remaining day was in August.

Table 3: The hottest days of 1999.
 
Rank Temperature (C) Location Date
1 35 Mildenhall 2 August
2 34 Mildenhall 1 August
3 32 Barbourne 31 July
4= 31 Gravesend 18 July
4= 31 Reading 30 July
6= 30 Gravesend 11 September
6= 30 Lee-on-Solent 11 July
6= 30 Lee-on-Solent 24 July
6= 30 Southampton 25 July

A brief comparison of the daily maximum temperatures in 1999 with Lamb weather types (Lamb 1972) for 1999 reveals that the highest summer temperatures occurred during types A, ASE, AS or SE and the lowest summer time maxima tended to occur when types C, NW or CN affected the UK. Types A, ASW, SW and S tended to dominate during the September heatwave, whilst many of the highest maxima during the spring occurred when types A, SW or ASW affected the UK. Types C, CN and CNE tended to be associated with the lowest maximum temperatures during the spring and NW, N or A types with the lowest maximum temperatures during the winter. The highest maximum temperatures were mostly recorded during types C, CSW, SW and W.

CONCLUSION
There appear to have been three noteworthy spells of relatively high temperatures in the UK in 1999. The first such spell occurred between the 4 and 6 January when temperatures reached at least 15C somewhere each day. During this period the high of 16C recorded in London on 6 January was the warmest January day there for 158 years. The period between 31 July and 2 August was the hottest spell of 1999; temperatures reached at least 32C on all three days and the high of 35C at Mildenhall (Suffolk) on 2 August was the hottest day of 1999 - the author believes to be the UKís hottest day since 1990. The third noteworthy spell of high temperatures occurred during the first half of September, when temperatures reached 30C for the first time during this month since 1973.

More than half of the 1999 daily highs were recorded in the Channel Islands, London, Penzance (Cornwall), Torquay (Devon), Poole (Dorset) or Herne Bay (Kent). A brief comparison between daily maximum temperatures and Lamb weather types revealed that the highest summer maximum temperatures occurred during A, ASE, AS or SE types, whilst C, CSW, SW and W types were associated with the highest winter time maximum temperatures.

With no other such study undertaken to the authorís knowledge, it is difficult to compare the national daily maximum temperatures of 1999 to those of other years. However, the author hopes to produce similar studies to this one in future years and then some hopefully interesting comparisons may be made.

REFERENCES
BRUGGE, R. (1999a): Monthly summary notes. Climatological Observers Link Bulletin, 356, 39-44.
BRUGGE, R. (1999b): Central England Temperature and England & Wales Rainfall Series update. Climatological Observers Link Bulletin, 356, 12.
DUKES, M. and EDEN, P (1997): Phew! What a Scorcher. in Climates of the British Isles Present, Past and Future eds. Hulme, M. and Barrow, E., Routledge, p454.
EDEN, P. (1991): Gunby, Lincs., Putting the Record Straight. Weather, 46, 331.
EDEN, P. (1995): Weatherwise. Macmillan, p323.
EDEN, P. (1998): Weather Log, February 1998.
EDEN, P. (1999a): Weather Log, January 1999.
EDEN, P. (1999b): Weather Log, September 1999.
HICKCOX, D. (1999): Temperature extremes. Weatherwise, 52, 56-61.
LAMB, H. H. (1972): British Isles Weather Types and a Register of the Daily Sequence of Circulation Patterns 1861-1971. HMSO, p85.
PRICHARD, B. (1999): TORRO thunderstorm report: May 1999. Journal of Meteorology, 24, 270-273.
WALTON, J. (1999): The weather of 1998. Outlook, January/February 1999, 10-11.
WEBB, J.D.C. and MEADEN, G.T. (1993): Britainís highest temperatures by county and by month. Weather, 48, 282-291.
WEBB, J.D.C. and MEADEN, G.T. (1997): Britainís highest temperatures for every day of the year, 1 January to 31 December. Journal of Meteorology, 22, 81-93.

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Dan Suri, 16 February 2001