Hotter than July? Data on how hot it should be at this time of year

Wikimania_2014_-_0803_-_Hyde_Park_-_The_Serpentine220917 Rainer Halama

The Serpentine, Hyde Park: © Rainer Halama ┃Creative Commons

London recorded the hottest July day on record today with the temperature climbing above 36 degrees at the weather station at Heathrow. As passengers on Tubes and buses suffered in the heat it was certainly, in the words of Stevie Wonder, hotter than July, or at least hotter than July usually is in the capital.

But what does one day tell us about summer temperatures and what is normal for July? At Urbs we turned our attention to weather data to find out. We looked at Met Office data for London for the month of July stretching back to 1948 and we found some interesting patterns.

Average July maximum temperature varied from below 20 degrees in 1954, 1965 and 1980, to over 27 degrees in 1986, 2006 and 2013.  2013 and 2014 was only the second time in the record when the average temperature was over 25 degrees for two consecutive years.

weather July average

The temperatures were recorded at the Met Office weather station at Heathrow Airport, the only one in London with openly available historic data.

Taking a 10-year rolling average gave a longer view on what’s happening to summer temperatures. The average maximum July temperature fell by almost a degree from 22.3 in the 1950s to 21.4 in the 1960s. It then rose steadily to reach 23.5 by the 1990s and has stayed around that level since.

weather july 10 year rolliing

The forecast says it will be about 10 degree cooler in a week’s time and with Wimbledon running later this year July is likley to have a fair share of rain. But today’s scorcher and the expected continuing heat of the next few days may mean those 2 consecutive years of plus 25 degrees will soon be 3.

Source data

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