The hottest July day on record was recorded at Heathrow airport on Wednesday 1st. The 36.7C recorded between 1500 and 1530 exceeded the previous record of 36.5C set at the Royal Horticultural Garden at Wisley, Surrey, in 2006.
I recorded 36.1C in Wanstead, a reading that exceeded the previous July record of 35.9C set in 1868 – indeed it was the fourth highest temperature this area has seen since local records began in 1848.
Already, however, questions have arisen over the validity of the Heathrow value mainly because the official measurement far exceeded that of Northolt, an airfield and the closest official station, which recorded 35.7C, a full degree cooler.
I’ve always been a bit sceptical on the validity of airport readings – there’s a lot more concrete at Heathrow than Northolt and obviously far more jet engines. The previous July record at Wisley is surely far more representative of standard conditions? I fear that with a new runway Heathrow will only get hotter and, perhaps, a review of the official MetO station should be taken.
I’m often asked why my own station is not used for official readings. The simple answer is that, being in a suburban garden, it is too sheltered to qualify for the open exposure that the Met Office demands.
But, apart from the exposure, everything is as representative as possible to conditions set by the Met Office. When readings differ it is simply because the character of the area is warmer or colder than official stations, the closest of which is St James’s Park.
To try to quantify this I’ve had a look at all the official stations around Greater London throughout June. The results show that readings from Wanstead are remarkably similar to other stations.
I first had a look at maxima which revealed that Wanstead is 0.3C warmer than Heathrow and 0.6C warmer than St James’s Park.
Minima, on the other hand, revealed that Wanstead was 0.5C cooler than Heathrow and 0.9C cooler than St James’s Park – a stark illustration of how much warmer inner London is than the suburbs.
This obviously had a bearing on the mean temperatures of the region, Wanstead being 1.1C cooler than Heathrow and 1.2C cooler than St James’s Park.
In terms of rainfall Wanstead was wettest, but only by 4mm.
So, all in all, the weather station at Wanstead is a pretty good measure of our local climate, as close as possible to what official conditions for measurement of climate demand.
I am currently in the process of trying to find a site local to the area that will fulfil Met Office conditions but it is a long, drawn-out process that will take time to organise.