As Heathrow is often the hottest area, it makes you wonder how well shielded or positioned the sensor is.
Originally Posted by: Rob K
Just where the planes' afterburners kick in.
Originally Posted by: NickR
I think it is just the fact that there is a vast expanse of tarmac and concrete which gets heated up by the sun and warms the surface layer of air. Even with a well shielded sensor, it will still be affected by all that warmth.
But you get a similar local effect with other surfaces too, for instance I was at Frensham Pond today which is in a dip (obviously) and has lots of bare dry sand that gets heated up by the sun. I bet if you put a proper Stevenson screen out there in the middle of the "beach" it would be a degree or two higher than surrounding areas.
Plus Heathrow is in one of the generally hottest parts of the UK anyway. In summer months the maxima usually go to places around the M25 to the west of London, e.g. Northolt, Wisley, Heathrow...
Originally Posted by: Matty H