Autumn 2011 United Kingdom heat wave
|High pressure caused warm air from Southern Europe to rise up towards the UK|
|Dates||25 September – 3 October|
|Areas affected||United Kingdom and Ireland|
|Highest temperature||29.9 °C in Gravesend, England|
The autumn 2011 United Kingdom heat wave was a period of unseasonably warm weather which arrived towards the end of September 2011 and continued into October. As a result, record high temperatures for the country were broken for the autumn months. The autumn heat wave followed the warmest temperatures to occur on record in the spring, but also the coolest temperatures to occur in the summer months since 1993.
Temperatures in most parts of the United Kingdom began to rise on 25 September, reaching 23 °C in some areas. The warm weather stayed consistent over the next few days and reached 27 °C at Saint Helier in Jersey on 28 September. Temperatures continued to rise and the temperatures recorded on 29 September exceeded those peaked in Costa del Sol, Turkey and Mexico that day at 29 °C in Lincolnshire. This also broke the UK's record high for that day of the year, with 27 °C having been recorded in York on 29 September 1985.
The month of October began with a southerly airstream resulting in some exceptionally high temperatures, reaching 25–28 °C throughout England and Wales. 1 October brought the highest temperatures of the heat wave with 29.9 °C recorded in Gravesend, Kent, the highest ever recorded in the United Kingdom for October, beating the previous October record of 29.4 °C which was set in 1985 in March in Cambridgeshire. The new record also made the first day of October the third warmest of 2011, although in several places (such as Sennybridge in Powys), 1 October was the hottest day of the year. The annual high temperature was broken in certain places in the west and north. Throughout the month, mild westerly and southerly airstreams brought rain to north-western UK, and further relatively warm and dry days in the south. The Central England Temperature for October was 13.02 °C, almost 2 °C above the 1971–2000 average, and was the warmest October since 2006 and the eighth warmest in 100 years. There was a marked contrast in rainfall, with amounts ranging from well below average over East Anglia and south-east England to well above in Northern Ireland and western Scotland. Subsequently, sunshine amounts also varied accordingly, from well below normal over Northern Ireland and western Scotland to well above in East Anglia. However, a cold front from the remnants of Hurricane Ophelia brought much cooler air across the whole of the country.
The unseasonably warm weather in the United Kingdom saw visitor numbers in Chester Zoo rise by 149% on 28 September. The heat wave also saw an increase of camping and caravan parks and hotel bookings in parts of the country, including Wales. Businesses in Winchester have also been said to have been favoured during the period, as a 67% tourism increase was recorded on 30 September from the same day in 2010. A negative effect for many UK businesses was a sales drop, and some clothing retailers suffered their largest for two years, as autumn and winter clothing sales decreased.
The BBC claimed that the unseasonable heat wave caused for low Strictly Come Dancing viewing figures on 30 September, with an alleged loss of one million viewers on the Friday in question. A similar pattern followed the following evening with X Factor on ITV.
Water companies predicted that, owing to the somewhat dry weather throughout 2011, a drought might occur during 2012 if substantial rainfall did not occur over the winter months of 2011–2012.
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