The summer of 1976 was the hottest ever recorded in the UK with a CET (mean temperature across representative stations across central England) of 17.8C but the reason it occurred started long before June 1976, which was the first of the three very warm settled summer months. A period of dry spring weather enabled the dry ground to absorb solar radiation very efficiently and heat up rapidly by day as a result. In fact, a warm June is quite an unusual event; we see the hottest day of the year in June only a quarter of the time and there has been little sign of any long term warming trend recently in June; if anything it has become duller and wetter. The hottest June on record in 1976 wasn’t that much warmer than the average July or August but nevertheless it is certainly remembered as being hot. This is perhaps partly as a result of the fact that the hottest weather occured in the last ten days of the month but it was quite dry and warm beforehand.
The month saw progressively rising temperatures in a long spell of quite calm and sunny weather dominated by high pressure. The 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. Whilst the month started damp by the 2nd as the Azores high ridged towards up and into the country the south became settled although and as it moved further east a southerly flow moved up right across the UK allowing temperatures to rise towards the mid to upper twenties centigrade. By the end of the first week given the constant sunshine and dry ground temperatures rose into the low thirties in parts of the south east, though the heat was not widespread. In fact, the middle of June was mixed with unsettled weather in the north but the high pressure remained across the south so these parts stayed dry.
It was the last ten days though of June that saw the real heatwave. High pressure developing across SE England allowing a continental flow from Spain and temperatures then exceeded 30C every day until the end of the month. From the 23rd June through until the first week of July there were 15 consecutive days when the temperature exceeded 32C somewhere in the country and five days exceeded 35C. On the 26th June 35.4C was reached at North Heath (Sussex) and East Dereham (Norfolk), this is the earliest date in the 20th century that 35C was exceeded. The old London Weather Centre in High Holborn, central London, also recorded a rooftop maximum of nearly 35C (34.8C) on the 26th, whilst Southampton’s Mayflower Park recorded a maximum of 35.6C on the 28th. Nights were particularly uncomfortable for sleeping especially in the cities with minima only falling to 20C at times. Brush and heath fires developed too across the south given the very dry conditions. The New Forest was particularly badly affected, as this 1976 clip shows http://www.youtube.com/watch?v=IHzhI2owHgM&feature=related. Many of the fires were caused by disarded glass bottles, the sun magnified by the glass would then ignite the very dry grass.
Even along the coast there were quite high temperatures reported as coastal breezes were suppressed by stable high pressure inhibiting convection of the hot air inland. Temperatures above 30°C were recorded at numerous coastal locations in the latter part of June.
The heatwave continued through the rest of the summer of 1976 as well and is still remembered by many in their forties and above now as being perhaps the most persistently hot spell in the UK in their recollection.