WMO03772, Heathrow (London airport)
51 28 45N 00 27 02W (51.47916444653322,-0.4505671614755646)Estimated Class 3. Innermost circle is 10 metre radius.
[update, enclosure hardstanding, paving, has not been appraised, may degrade the Class, see Llanbedr articles ]
UHI, both local and distance, major airport close to dense urban, city, transport links. Includes 4 lane underpass tunnel, North entrance in image top left, equipment building to left with standby generator and air conditions. Since the image blast screen has been installed changing environment during installation (see Google image history shown below). Is in heavy passenger or freight jet blast area, although probably of minor effect.
This is a site known on the Talkshop and known bad. Unfortunately Microsoft are at it again and have broken their own Silverlight so I cannot use their ground level view (used to work) where it is known there are good images of the met site.
Following images all (c)Google and their providers. Image date (approximate) is shown top left. There is a date problem with Google!
First the tarmac vehicle parking appears, open to gas passage.
Then a blast screen is installed.
“Thursday, Aug 30 2012 …
The highest-ever temperature in Britain has been recorded, weather forecasters said.
A temperature of 37.4C (99.3F) was recorded at Heathrow around 1.30pm, the London Weather Centre said.”
http://www.dailymail.co.uk/news/article-191830/Sizzling-UK-records-hottest-day-ever.html
Figures as a hot site many places, BBC of course.
You might like to look at the Google year 1945 image. Fields to the north then but it already was an aerodrome.
[update]
The Met Office have promotional images, one of the Heathrow met site except for some mysterious reason the camera is pointing at the runway, doesn’t really show the met site. Strange people
Need to dig that out sometime.
(c)Crown Copyright, PDF dated 2008 setting last date possible of image. From “National Meteorological Library
and Archive
Fact sheet No. 17 – Weather observations”
Contributor Caz found the document http://cedadocs.badc.rl.ac.uk/270/1/factsheet17.pdf at Rutherford Laboratory (RAL these days, worked there briefly many years ago) [/update]
Tallbloke's Talkshop 
“Is in heavy passenger or freight jet blast area, although probably of minor effect.”
Jets have got bigger as passenger numbers and freight volumes have risen. I’d be interested to hear your reasoning for the backwash being a minor effect though.
Stevenson Screen at Heathrow, about quarter of the way down.
Click to access factsheet17.pdf
[ thanks, updated article ]
Bing Street view. Little wonder this site records record high temperatures.
link to bing
[mod changed long link]
There’s also an air conditioning plant on the “Carillion building” next to the met station. Not sure what the blue boxes on the ground are but they have ventilation grills.
http://www.bing.com/maps/?v=2&cp=51.479382~-0.450582&lvl=19&dir=0&sty=x~lat~51.479382~lon~-0.450582~alt~73.43~z~30~h~236.9~p~-8.8~pid~5082&app=5082&FORM=LMLTCC
[…] the Met Office have edited their Factsheet number 17. This has been mentioned on this site (here) and a search shows mention in a comment at chiefio’s (here); the photo in the document […]