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New Data From Ruislip Casts More Doubt On Heathrow “Record Temperature” Claims

July 5, 2015

By Paul Homewood 




The plot thickens!


I asked the Met Office for the detailed list of temperature readings at Heathrow around the time of its record on Wednesday. They put me on to the WOW site they operate (Weather Observations Website).

Unfortunately the only two readings they have recently for Heathrow and Northolt are one on 15th June and the other at 9.00am on 1st July. They tell me they have system problems!!


But, most usefully, WOW offers full data, at 5-minute intervals, for Ruislip, which was one of the stations I compared to Heathrow a couple of days ago.

I must stress that the Ruislip site is not an official Met Office site, but is run by a “hobbyist”, so we need to be cautious not to read too much into it. What is significant though is that it confirms the data from the Gladstone database, which showed that the max temp at four sites within seven miles of Heathrow all peaked at between 95.0 and 95.2F. This was much lower than the claimed record at Heathrow of 98.1F (36.7C).

[The only difference between the Gladstone and Met Office databases is that the former, for some strange reason, is on GMT, so is an hour adrift]


Looking at the WOW temperature measurements at Ruislip, around the time the record was set at Heathrow, we see:







I was concerned previously that once or twice hourly measurements may have missed a large spike in temperature, but these 5-minute readings are now the final part of the jigsaw.

Ruislip is just seven miles from Heathrow, and the WOW coordinates confirm that this is the same station as used by Gladstone. 

The temperature at Ruislip peaked at 35.11C between 14.50 and 15.00, i.e. 95.2F. This is, of course, well short of the 36.7C recorded at Heathrow  . 


There is now ample evidence to suggest that the Heathrow record temperature is not an accurate or valid one. It is now surely time that the Met Office withdrew their dubious claims until such time as they have fully investigated it and proved conclusively that it is a genuine temperature reading reflecting meteorological conditions, totally unaffected by extraneous factors.





I have just had a reply from the Met Office to my request for the temperature data at Heathrow for that day:


Hello Paul

I am afraid this information is simply not available without a charge.

If you fill in the form below I can get you a free non obligation quote?

Prices for our data start from £75 + Vat (for a simple weather summary based on “2km x 2km grid square” modelled data), through standard monthly summary reports of daily information ranging between £110 + Vat to £180 + Vat, with a significant amount of requests, requiring more specific data (e.g. actual weather station data), costing from approximately £200.00 + Vat.


A suspicious person would think they are trying to prevent the public from accessing data, which they have already paid for through their taxes!

  1. Joe Public permalink
    July 5, 2015 2:19 pm

    Unlike all the other temperature stations local to Heathrow, the airport is most likely to be affected by heat emissions from fuel burnt by aircraft taking-off & landing.

    Perhaps the Met Office can advise what that heating effect is.

    Aircraft movements take place between 04:30 and 23:30. There are ~1,400 movements per day, say 73 per hour.

    1. 37 take-offs per hour.

    2. A 747 uses approx 1 tonne of fuel per take-off. Smaller aircraft will use less, so lets assume an average of 0.5 tonne per take-off. Aircraft taking-off will therefore consume ~18.5 tonnes/hr.

    3. Aviation fuel has a calorific value of say ~46GJ/tonne

    4. One GJ ~12,750kWh

    5. 18.5 tonne/hr x 12,750 kWh= 235,875 kW per hour, heat produced.

    6. Assuming just 50% is warming the air in the immediate vicinity of the aircraft, and thrust at the runway, and downwards during take-off. >> say 118,000 kW

    7. 118,000 kW will raise the temperature of a cubic kilometre of air by 0.35K

    8. To the heat produced by aircraft taking off, must also be added the heat produced by aircraft landing (reverse thrust). For argument’s sake, say 5%.

    9. 0.35K x 1.05 = 0.368K

    10. In addition, those 73 aircraft manoeuvre around the apron before & after landing, adding say another 5%.

    11. 0.368K x 1.05 = 0.386K

    12. There are many variables, but unless someone can point out glaring errors in the above assumptions, discharging 120 – 200 MWh of heat in the vicinity of a thermometer must have some tangible effect.

    • July 5, 2015 3:50 pm

      (i) There’s no such unit as kW per hour.

      (ii) Do you mean that 118,000 kW will raise the temperature of a cubic kilometre of air by 0.35K per hour?

      (iii) The merit of your model depends on there being a static cubic kilometre lump of air at Heathrow, whereas you need to allow for any zephyr, breeze or gale blowing.

      (iv) Set aside your model: you’re right – jet exhausts, tarmac, concrete, cars, buses, and trains undoubtedly bias readings upwards, and not by trivial amounts.

      • Joe Public permalink
        July 5, 2015 7:32 pm

        1. From the assumptions & calculations the heat produced in one hour is of the order of 235,875 kW. It was written as a duration, not as a ‘unit’

        2. No. 118,000 kWh will raise the temperature of a cubic kilometre of air by ~0.35K in one hour. [Or, e.g. a tranche 500m x 500m x 100m by 14.09K]

        3.1 The ‘model’ was simply an endeavour to give an indication of how an air-temperature measuring station Heathrow Airport is affected by the activities unique to the world’s 4th-busiest airport, especially when compared with locations having no air traffic.

        3.2 The model doesn’t “depend on there being a static cubic kilometre lump of air at Heathrow”, because ~235,875 kW of heat is on average, being produced each and every hour throughout the 19-hour working day.

        3.3 My skills are incapable of “allow(ing) for any zephyr, breeze or gale blowing.” But that heat has to go somewhere. I accept that the majority will rise, and/or be blown away from the thermometer by zephyr, breeze or gale. But those same zephyr, breeze or gale will occasionally blow some of that heat towards the thermometer. [

        4. Thanks for “you’re right – jet exhausts, tarmac, concrete, cars, buses, and trains undoubtedly bias readings upwards, and not by trivial amounts.” The calculation was simply a first cut at quantifying ‘trivial’ / ‘non-trivial’.

        I don’t know for certain, but presume there are actually more than 73 aircraft-movements/hr during the afternoon, than early morning and late evening. This means that heat discharge would also be proportionately greater during the naturally-hottest time of the day.

        It seems the furore is about a ‘spike’ in measured temperature. Perhaps a gust of wind directed some of that 235,875 kW to increase the already-high thermometer-reading by sufficient to indicate a new ‘record’. As Stephen (at 3:03pm) below points out, the peak was timed at a minute-by-minute resolution, so the gust could have been quite brief.

        In one discussion that appeared on Twitter, a Met Office CliSci indicated that there was “no strong evidence for that (a warm gust of jet exhaust) in the data”. But failed to reply to a question “How would anyone know?”

      • July 6, 2015 1:53 pm

        “1. From the assumptions & calculations the heat produced in one hour is of the order of 235,875 kW.” But a kW is NOT an amount of heat, it’s a rate of heat production.

  2. stephen permalink
    July 5, 2015 3:03 pm

    Is it possible that changes in observation practice made this a record?

    First, I noticed the peak was timed at high resolution of 3.13pm. Do all current stations measure at minute-by-minute resolution? How long have such high-res measurements been used, back to 1990 or 1995 or 2003 or 2006?

    Second, Heathrow has got busier and busier meaning more jets and more intense urban heat island effect in surrounding area. If there was a third runway then I predict more ‘records’ in the future.

  3. July 5, 2015 3:11 pm

    Thanks, Paul, Joe Public.
    Yes, all those airplanes taking off must cause a tremendous heat island. Thus, the readings must, of course be adjusted up!

  4. July 5, 2015 4:31 pm

    Looking at Ogimet I notice that Heathrow is 1.4C higher than Northolt, another airfield. At 4pm it was 35.9C to Northolt’s 34.5C.
    There’s a lot more concrete at Heathrow and obviously far more jet engines. Is it possible that this reading is too high. The previous July record was set at an RHS garden in Wisley, 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.

    In Wanstead (22 miles ENE of Heathrow) my July record was broken: 36.1C (exceeding the old record for this area, 34.5C set on 15th July 1881. Camden Square recorded 35C the same day)
    My Casella ‘check’ mercury in glass thermometer recorded 35.8C – the station is set up in a standard wooden Stevenson’s Screen in a suburban garden

  5. Bloke down the pub permalink
    July 5, 2015 5:15 pm

    I am afraid this information is simply not available without a charge.

    The bloody cheek. Questions ought to be asked in the House. Perhaps the Met Office think that the millions of pounds thrown at them over the last few decades to study cagw aren’t sufficient. Or maybe that the tap would be turned off if the public were to question the veracity of their pronouncements.

  6. July 5, 2015 5:59 pm

    Here are the half hourly decoded metar reports from Heathrow for 1 July 2015. The highest temperature indicated is 95 F, which was decoded from 35 C. The metar data was decoded from whole degrees C, therefore you see steps of 2 F in the decoded data (91, 93, 95, etc.):


    UTC Temp(deg F)
    01 EGLL SA 1220 UNL 88 57 150 13 29.86 0
    01 EGLL SA 1250 UNL 91 57 120 12 29.86 0
    01 EGLL SA 1320 UNL 95 54 160 11 29.83 0
    01 EGLL SA 1350 UNL 95 52 150 13 29.83 0
    01 EGLL SA 1420 UNL 95 52 170 14 29.83 0
    01 EGLL SA 1450 UNL 93 55 150 14 29.83 0
    01 EGLL SA 1520 UNL 93 55 180 14 29.83 0
    01 EGLL SA 1550 UNL 95 55 160 11 29.83 0
    01 EGLL SA 1620 UNL 93 55 170 13 29.83 0
    01 EGLL SA 1650 UNL 93 55 160 14 29.83 0
    01 EGLL SA 1720 UNL 93 52 160 14 29.83 0
    01 EGLL SA 1750 UNL 91 54 170 11 29.83 0

    • July 5, 2015 6:36 pm

      It sounds like Brogdale all over again, though that obs was seen until the end of August 2003 when it was sent in the traditional way by Met Form

  7. Billy Liar permalink
    July 5, 2015 6:50 pm

    By stepping hourly through the daily summary on the page linked below it is possible to determine that the 36.7°C occurred between 17:00 and 18:00 UTC ie between 6pm and 7pm local time.

    Seems a bit fishy since the 1720UTC and 1750UTC METARS were respectively 34°C and 33°C.

  8. July 5, 2015 6:57 pm

    Data schmata. Countryfile had the ‘hottest July day’ graphic up. Keep saying it ahead of Paris non?

  9. Dave Nunn permalink
    July 5, 2015 7:10 pm

    Wouldn’t a standard FOI request suffice. Provided the requested data is transmitted electronically there should be no charge. I’ve made FOI requests on other matters and never been charged irrespective of the work involved.

    • July 5, 2015 9:26 pm

      I’ll see if I can get it from KNMI first (they are a week behind). But, yes, I have had to use FOI before when they have stonewalled me.

      • Joe Public permalink
        July 5, 2015 10:31 pm

        Paul, if you do FOI the MO, will you ask what effect they’ve calculated, for the impact of jet-fuel combustion heat emissions from aircraft movements at Heathrow?

      • Joe Public permalink
        July 5, 2015 10:32 pm

        And, from what start date.

  10. Billy Liar permalink
    July 5, 2015 7:22 pm

    The Heathrow weather instruments are located at 51.479N 0.449W right between the northern perimeter road and runway 27R, 50m west of the Nene Road junction. At the relevant time the wind was blowing from the large patch of concrete housing terminals 1, 2 and 3; the wind direction was between 160° and 200°. Aircraft engine exhaust would also be blown from the runway in the direction of the met instruments regardless of the direction of take-off. Aircraft would still be on the ground taking off to the west. Landing to the east it is possible that the last high-speed taxiway on 09L might be taken, in which case the engine exhaust is aimed straight at the met instruments. The runway exit before that one is not a high-speed turn off but aircraft exhaust would be directed at the met instruments from 170m away and aided by prevailing wind.

  11. Billy Liar permalink
    July 5, 2015 7:32 pm

    Anyway, according to BEST you’ve got to use the ‘scalpel’ to scythe away these outliers to get to the ‘truth’.


  12. July 5, 2015 9:38 pm

    Heathrow (if you can’t see it look for M25 sign) looks different than the surrounding area. Clearly it will tell us everything we need to know about our climate 😉

  13. July 6, 2015 10:12 am

    Funny how ‘system problems’ are preventing the data from appearing at their WOW site, but that they are magically available (reconstructed?) if you send money…

  14. johnmarshall permalink
    July 6, 2015 10:20 am

    I am afraid that GMT is the SOP time for Met reporting, so the whole world operates on the same time standard

  15. Dave Ward permalink
    July 6, 2015 12:02 pm

    Having spent some time looking at various airfields on, and watching the movements at Heathrow for the best part of an hour last night, it’s apparent that in (the prevailing) Westerly winds runway 27L (the Southern runway) is used for landing, and 27R (the Northern runway) for take-offs. This means that the Met station is going to get the maximum warming effect from aircraft under full power whenever there is any Southerly component to the wind. It is close to the point at which the larger aircraft rotate into a climbing attitude, and that is when wake vortices start emanating from the wing tips. These would help to spread the heat to each side, even in light winds.

    I am not sure what happens when the wind is Easterly, or even if the landing/take-offs are switched to the opposite runways at certain times, but there seems little doubt that readings from the airfields own Met station are going to be unrepresentative of the wider area. From a pilots perspective the actual temperature his (or her) aircraft is experiencing is critical, particularly during a fully loaded take-off, but I do wonder why they didn’t site it between the two runways – at least this would give a more uniform figure. As for the number of movements per hour – this obviously varies somewhat, but I might get comfortable later, and count them!

  16. Dave Ward permalink
    July 6, 2015 12:41 pm

    Oooops – should have checked before hitting the keyboard. According to this document: they DO alternate runways, at 15:00 each day, but only during “Westerly Operations”. According to the handy “” site it appears that July 1st would have presented Heathrow with a moderate SE wind, so they would probably be landing/taking off to the East. But from which runway I’m not sure. However any jet exhaust would certainly have found its way to the Met Station…


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