Last Time 30C plus was recorded

[johnholmes]

Met O quote 30.9C for London on their web site

[The PIT]

I'm sure Carol K said 31.1C this morning.

[Essan]

Met O quote 30.9C for London on their web site

London Weather Centre - non standard exposure and does not count for official figures. So far as I know the official max yesterday was 29.6c at Charlwood.

I expect we will see a number of 30s today though

[Cookie]

I dont understand this how can anyone get the correct figure and what is classed as official?

[Cookie]

according to this again 30oC

24 hours ending 2200 on 28 Jul 08: UK

Highest max 30.2 °C London

Lowest max 14.9 °C Wick Airport

Lowest min 6.8 °C West Freugh

Highest rainfall 19.2 mm St Athan

Sunniest 13.9 hours East Malling

Last updated: 0001 on Tue 29 Jul 2008

[acbrixton]

Cookie, this area is confusing.

1. The WMO (of which the MO is a member) lays down guidelines as to the location of recording instruments/Stevenson Screens. Essentially they should be located far enough away from 'significant obstructions' such as trees and buildings to ensure that there is minimal distortion caused by shelter from trees or localised heating from buildings.

www.met.reading.ac.uk usefully list 8 types of exposure only three of which are acceptable for producing reliable data ('standard exposure'). The minimum acceptable standard requires that recording instruments must be at least twice the distance from the height of any 'significant obstruction' such as trees or heated buildings. That site states "Rooftop sites for temperature and rainfall sensors should be avoided where possible".

2. London, or more accurately the London Weather Centre ('LWC'), records data from an asphalt roof and is thus does not comply with the requirements for standard exposure. Other London sites (past and present) such as Heathrow, London City airport, Kew Gardens, Greenwich Observatory, Hampstead and St. James Park are/were examples of standard exposure.

3. It follows that data from LWC cannot be used by the MO when compiling reliable data (e.g. monthly highest maxima, local/regional mean temperatures et.). However, confusingly, the MO/BBC forecasters make use of LWC data when preparing daily summaries or giving an overview of the previous day's weather.

4. If no other station records 30c this summer then it will follow that 'officially' 30c was not recorded as LWC is non-standard.

5. A further complication arises from the fact that the frequency with which individual stations report their daily data to the MO vary hugely from hourly to once a day. This means that daily summaries such as those posted on the BBC News online at about 11pm will lack data from a number of stations that report data for a particular day the following day.

6. Finally all reported data are subject to revision/rejection by the MO where they are unhappy with, for example, the accuracy of an individual station's recording equipment or the manner in which readings were made. It is therefore best to await the publication of the MO monthly summary in the first week of the following month before one can be confident of knowing whether a particular temperature was reached in the preceding month.

regards

ACB

[Interitus]

Perhaps for consistency....if they recorded it at a non-standard time, it is not counted since most of the rest of the country and the world reports only at hourly or 30 minute intervals.

Really though it's funny that we have to scratch around in the dirt so desperately to find a 30C to cling to!

Maximum and minimum temperatures aren't recorded at 'standard' times as they would most likely be missed, they over a period of say 6 or 24 hours.

[Nick H]

The highest temperatures under standard conditions yesterday were 29.5°C at both Heathrow and Northolt.

they should be located far enough away from 'significant obstructions' such as trees and buildings to ensure that there is minimal distortion caused by shelter from trees or localised heating from buildings.

It's an odd phrase that. Surely a strict interpretation of it would preclude the location of recording instruments in any city centre.

Heathrow, being an asphalt jungle, is certainly not representative of the surrounding area.

The silly thing is that if the Clerkenwell station were located at street level it would probably record higher temps than it does from the roof.

Edited July 29, 2008 by Nick H

[johnholmes]

always a difficult one as to what is Representative and what is not.

From my time in the Met office the siting of observing sites was always a very tough one, as was the continuance of observing from long established sites. Manchester airport was a classic from the 1940's into the late 60's and 70's as the concrete areas around the main observing site increased. Was the site still representative or not? After prolonged discussion at local and national level we decided it was as good a site as could be found at the airport so it was kept, an oasis of grass in the middle of a concrete jungle. Heathrow, Gatwick, Stansted, Birmingham, all had and have the same problem, also some of the RAF stations.

As to the weather centres, again, after much discussion it was decided that, whilst they could not be used in the strict 'official' sense, they were representative of temperatures for many living and working in large town and city environments.

hope that helps explain some of the background.

As to non 'official' sites which are quoted in the Met O for statistics, believe me when I say they are given a very strict check before they are given their status and are regularly checked both for site changes and accuracy of their equipment.

Edited July 29, 2008 by johnholmes

[J07]

If I recall correctly, the standards are that the station must be no more than xH from any nearby building/tree, where H is the height of the obstacle and x is some factor (can't remember if it's 1.5, 2 or 3 or something along those lines!). These standards may be for anemometers though, as opposed to Stephenson Screens?

Personally I think that inner city AWS' are hopeless. People *know* that cities trap heat and concrete jungles continue to spew out their long wave radiation at all hours, completely skewing night-time temperatures as well. If we start believing these sorts of values then we may aswell allow observations to be taken in the centres of overcrowded cities in equatorial and tropical regions. The net effect would be that our "tolerances" would go up. Record temperatures the world over would have, say, 5C added to them, 30C would become relatively mundane in the UK and instead we would start getting excited about temperatures like 35C or 40C.

I know that every summer someone will say it was over 40C, and it will make it onto the news, this year I remember it quite well. "No rain for three weeks, grass has stopped growing, and temperatures of over 40C". It's obviously complete claptrap but it isn't helped by non-standard stations being reported as a matter of fact. For most people in the UK, the BBC will be their only source of weather information, and when they use London Weather Centre readings it just starts to slightly degrade the actual meaning of temperature.

I'm going way over the top really, but I do think it's important to have standards and maintain them, otherwise lots of data from the past becomes less valuable and the public become increasingly confused about temperatures.

[johnholmes]

see my post above in which I tried to explain that this is done and the exceptions

for more info link to the Met O web site and download the details

[Cookie]

Cookie, this area is confusing.

Thanks mate for going to all that effort for me, It did clear things up a bit more <_<

always a difficult one as to what is Representative and what is not.

thanks john as well for you input :lol:

[Nick H]

The highest temperature in July was 29.7°C at Kew Gardens on the 27th.

[The PIT]

So disregarding the official unofficial official roof temp still no 30C recorded as of yet.

[damianslaw]

Yes I was reading Philip Edens review of July and he also stated the official high for the month being below 30 degrees. The odds of a 30 degree figure occuring tends to decrease markedly only once you get to late August, so plenty of time yet, although going from the synoptical outlook it will need a marked change to occur towards mid month for the chance of 30 degrees to be recorded this year.

[Interitus]

According to the Met Office review for July, the 29.7 at Kew Gardens on the 27th was surpassed by 30.2 °C at Cambridge NIAB on the 28th.

[Optimus Prime]

Much like last years supposed 30c I find it a little suspicious.

[acbrixton]

Much like last years supposed 30c I find it a little suspicious.

OP what are your grounds for finding either of the 30c plus readings "a little suspicious"?

regards

ACB

[The PIT]

OP what are your grounds for finding either of the 30c plus readings "a little suspicious"?

regards

ACB

Agreed is this another of those unofficial official unofficial sites????

[Interitus]

On the contrary, it is based at an agricultural research institute and the Met Office has weather data since 1959.

[The PIT]

On the contrary, it is based at an agricultural research institute and the Met Office has weather data since 1959.

Ah so it could be buried in a pile of steaming Cow dung then. I'm not being serious by the way.