The incredible heat-wave of 23rd June/8th July 1976

After a hot day on 22nd June 1976 (maximum temperature 26.3°C) a remarkable heat-wave commenced in Royston during which the temperature reached or exceeded 30°C every day from 23rd June to 8th July (i.e. a consecutive 16 day period). The sequence was broken on 9th July when a temperature of 'only' 25.6°C was attained. The rest of the month remained very warm, however, and a mean daily maximum temperature for July of 25.6°C was achieved. The equivalent figure for June was 24.4°C.

Given that days with over 30°C are relatively unusual in Royston, and have occurred only in 12 years in the last 28 years (1972 to 1999), this was indeed a remarkable hot spell. It is difficult to envisage this ever occurring again, but if it has happened once then it is always possible it will be repeated, of course, however unlikely it seems. The return period for such an event must be 100 years at least.

The graph below shows the daily maximum and minimum temperatures recorded over this period.

In the period 1972 to 1999 the next longest consecutive sequence of days with over 30°C occurred between 29th July and 3rd August 1995 (6 days). The only other notable periods where the temperature exceeded 30°C on consecutive days were 8th/12th August 1997 (5 days) and 1st/4th August 1990 (4 days). This latter sequence included the highest temperature (35.0°C) recorded in Royston since 1972.

To help put the 1976 hot spell in context the following table shows the number of days each year since 1972 exceeding 30°C, and also the highest temperature attained each year with the respective date.

Year	No. of days with temperature 30°C or above	Highest temperature (°C) in year	Date
1972	0	27.2	18th July
1973	1	31.1	16th August
1974	0	25.2	15th August
1975	5	32.6	7th August
1976	18	33.7	26th June
1977	0	27.0	4th July
1978	0	26.7	31st May
1979	0	28.2	27th July
1980	0	27.8	4th June
1981	0	27.7	5th August
1982	0	28.6	9th July
1983	3	31.5	15th & 16th July
1984	0	29.0	28th July
1985	0	27.5	1st October
1986	0	28.5	27th & 28th June
1987	0	28.5	21st August
1988	0	29.0	7th August
1989	1	31.9	22nd July
1990	7	35.0	3rd August
1991	0	29.0	1st September
1992	0	28.5	29th June
1993	0	27.0	8th June
1994	2	32.0	12th July
1995	15	33.3	1st August
1996	4	31.5	222nd July
1997	6	31.1	8th August
1998	1	30.5	10th August
1999	2	30.9	2nd August
2000	1	32.0	19th June
2001	3	30.9	29th July; 15th August
2002	2	30.8	29th July
2003	7	36.4	10th August
2004	2	30.7	8th June
2005	4	31.7	19th June
2006	10	35.2	19th July
2007	0	29.8	5th August
2008	0	29.1	28th July
2009	0	29.1	1st July
2010	1	31.3	9th July
2011	1	31.5	27th June
2 2012	2	31.4	118th August

It can be seen from the above table that the hottest day of the year does not always occur in one of the recognised SummerImonths of June, July or August (see 1978, 1985 and 1991)! Also the 1990s have shown a marked increase in the days exceeding 30°C after only 4 such days in the 13 years from 1977 to 1989f(evidence of global warming?)ence June, July or August!