A summer heat wave

  • Image 1: People seen enjoying the summer weather. Photo by Sean Dempsey/PA Wire/Press Association Images

    Image 2: A map of the forecast temperature anomalies across the UK on Sunday 7th July 2013

    Image 3: A satellite image showing clear skies over large areas of the UK at 14:30 on Saturday 6th July 2013

  • A summer heat wave
    06.07.2013 14:02

    As we come to the end of the first week of July, summer appears to have finally arrived with many parts of the UK experiencing above average temperatures and plenty of sunshine. In the wake of the past few summers, a prolonged spell of settled weather with minimal precipitation and above average temperatures and sunshine has become somewhat of a rarity. In fact, it was seven years ago, in the summer of 2006, when the UK last saw prolonged ‘heat wave’ conditions (with temperatures reaching 36.5C at Wisley in Surrey on 19th July).

    A heat wave is defined in various ways across the world, depending on regional climate, among other factors. The World Meteorological Organization (WMO) defines a heat wave as five or more consecutive days in which the average daily maximum temperature is exceeded by at least 5C. Image 2 (on the left) shows a snapshot of forecast temperature anomalies across the UK on Sunday. It can be seen that almost all locations are predicted to be warmer than average with a few locations set to be 7C above average. Meteorologically speaking, summer in the northern hemisphere takes place between 1st June and 31st August each year. This marks the period when the UK typically experiences the highest temperatures and is the time when heat wave conditions are most likely.

    A combination of factors determines a prolonged spell of fine and very warm weather in the UK. Unlike recent summers, the jet stream has tracked to the north of the country, thereby allowing high pressure to build across the UK from the south. In doing so, any rain-bearing weather fronts from the Atlantic are forced to north and temperatures steadily rise under sunny skies.

    Remembered for its hosepipe bans and soaring temperatures, the summer of 1976 was notably hot with persistent anticyclonic weather patterns over the UK. Following an already exceptionally dry 12 months, heat waves exacerbated droughts with some areas seeing no precipitation at all for more than a month at a time. Not only was this summer overall the hottest on record, it also broke the record for highest June temperature, with 35.6C recorded at Southampton on the 28th.

    The European heat wave of 2003 was perhaps most influential on France, where approximately 15,000 people lost their lives as a result of the heat. However, the effects were also remarkable across the Channel, breaking the record for the highest temperature recorded in the UK (38.5C in Broadgate, Kent on 10th August) – a record that is yet to be beaten! Temperatures exceeded the 30C mark in various locations across the UK on ten separate days during that summer. Around 2,000 heat-related deaths occurred in the UK and wheat production fell by 12%, prompting the Department of Health and the Met Office to create the ‘Heat-Health Watch’ – a project which aims to give advanced warning of hot weather between 1st June and 15th September each year.

    As the area of high pressure retrogresses slightly westward in the coming days, a slight change in the orientation of the isobars will bring cooling northerly breezes to North Sea coastal areas with highs of just 14C forecast in some places on Wednesday. Nevertheless, with the anticyclone showing no clear signs of movement in the next ten days or so, plenty more dry, fine and warm weather can be expected across large parts of the UK; news which may not be music to the ears of many farmers, following the driest June since 2006.

    By: John Lee