Met Office: UHI and Hottest day at Heathrow [2013]

Posted: July 12, 2013 by tchannon in Surfacestation, weather


The dear Met Office have been pushing over the past few days about HOTTEST EVER THIS YEAR. Face it Met Office, enjoying life does not involve screaming or fear unless you are a kid.

Current 2013 UK maximum temperature confirmed

The current 2013 UK maximum temperature was recorded on Saturday 13 July, with 31.4 C at Heathrow. Wales also saw its highest 2013 temperature with 30.2 C at Llysdinam. The previous maximum of 29.9 C from Monday 8 July, at Edenfel, remains the current highest for Northern Ireland. Scotland saw its highest 2013 temperature on Tuesday 9 July, with 28.7 C at Strathallen Airfield. Issued at 2319 on Sat 13 Jul 2013.

Heathrow like most temperature breakers is a defective site. How about fixing it?


Image coutesty Met Office

The Met Office use peak reading for extremes, signal processing is not a subject here. Looks like the peak was around 5PM local time, wind had dropped slightly and was from the north, passing over a lot of dark asphalt before landing on the Stevenson screen. I don’t know whether is a Met Office PVC special or not.


Wind is critical, a howling gale picks up little heat.

Maximum temperature is least affected by UHI except for a classic fingerprint where the diurnal shape is skewed with the peak occurring later in the day then it would without UHI, the effect of thermal mass.

Minimum temperature is most affected by UHI as thermal mass slows nocturnal cooling.

The mean is skewed high.


Here is the Chilbolton Observatory data, because it is easy for me to do. It is also rural but not that far from London. I’ve checked Met Office sites as best I can to get a feel for things (they refuse to publish).

Chilbolton is not a weather station, nor using standard conditions but it is professional equipment and I have a pretty good idea of how it relates.

This plot shows humidity came up strongly so much that liquid water figures, there was hazy cloud cover (confirmed here), Heathrow shows some cloud. This has muted temperature peaking and reduced outgoing LWIR. Spot zenith IR thermometer peaked at about -2C here.

Look at the shape of the temperature peak, pretty much to insolation +3 hours, wind is similar to Heathrow, degree or so cooler which sounds about right (slight altitude effect too).

Now look at the previous night. Chilbolton has been dropping to below 10C some nights, about 10C (50F) this time. Heathrow data is showing 16.1C minimum. Wind dropped both places, with Heathrow still getting heat from the massive hardstanding area (Chilbolton also has hardstanding and radar dish).

Is it 6C of UHI, 3C mean? This looks excessive. Without full information it’s not possible to know.

A crazy thing as far as AGW is concerned is fussing about peak daytime temperatures but those too are least affected by the asserted CO2 effect, quite ridiculous. It’s minima which ought to show the effect, where UHI has most effect.

Northern Ireland

Not letting them get away with that one.

Superb Bing view of Edelfel where we see a stepped terrace and the area heavily surround by woods, poor exposure. Historically Google show no screen there but there seems to be one tucked tight in vegetation near the house and can’t find it earlier. (rough co-ord 54.5933 -7.28317)

Not an AWS, daily manual so maybe the screen walks.

Hot day, sure, scratching for tenths when the thermometer is not that accurate, go check the BSI.

As a site assuming that was the screen location it’s reasonable but this is about making points over hottest for the record.


I’ve held off on posting station information recently, too easy to deluge the blog. I could do this on my own blog but exposure is tiny. Any ideas?

There has been a sorry tale over the dreadful Met Office Solent site, day after day of hottest in the UK, exactly as I predicted when the wind is from the north or east where there are building very close, is a sun trap. Surrounding stations prove the situation.

Weather is set to continue hot, blocking weather. Expect higher temperatures.


  1. […] Met Office: UHI and Hottest day at Heathrow ( […]

  2. tchannon says:

    I’ve dropped the publish date back two days so that Rog’s context is at the top. Also added [2013] to the title, in hindsight it was misleading, not intended.