Although the Met Office say that the net differences are in the order of < 0.05C.

link

A lot of people think that 56.7C in Death Valley is wrong and likely some kind of recording error.

How much of an outlier is it? I would have expected the WMO to have subjected it to the same degree of scrutiny as they did the previous surface temperature record holder, so surely it can't be that dodgy?

I believe there are higher recent surface temperatures indicated by satellite measurements for the Lut Desert in Iran. But in the absence of a nearby surface station, the earlier record stands - because land skin temperature cannot be directly compared with air temperature.

That's just the mean difference between wooden and plastic stevenson screens, they were evaluating the effects of switching to plastic, to lower maintenance requirements. The extreme differences, however, were (obviously) greater than the mean but still acceptable and the plastic came out slightly better than the wooden, as I said.

All Stevenson screens read high in bright sunshine and light winds. Occasionally, they read a bit low when temperatures are increasing rapidly, due to thermal inertia, when compared with modern smaller aspirated multi-plate screens that are becoming more widespread.

But it's more common for Stevenson screens to read high i.e. in bright sunshine and light wind conditions, by up to 2 degrees C or so. Here's an extract from one of the official reports: Natural ventilation effects on temperatures within Stevenson screens (Reading University, 2010)


Add to that the faster response time of modern platinum resistance temperature sensors, such as they have (in a Stevenson screen) at Heathrow and it's not really surprising that Heathrow to name but one may tend to have an increasing frequency of record or near record temperatures. The old style mercury thermometers react more slowly and would sometimes miss the moment when the maximum temperature occurred, but the greater error on extremes remains, as always, with the Stevenson screen itself.

The problem of deviation between screen and actual appears to be directly related to ventilation, and I'm not convinced that either the Met Office or the report you linked to, is concluding that there is a significant difference between old wooden and newer plastic screens, in terms of temperature accuracy.

For the purposes of the thread, you appear to be deliberately interpreting the data as meaning that there was a definite strong upwards deviation at times of very high temperature, of up to 2 degrees C, thereby casting doubt on old records, and due entirely to the style of screen design. Whereas that is not what either report is saying.

The conclusion of the report you linked to, for example, refers mainly to a deviation at times of minimum temperature due to poorer air circulation. No strong reference is made to maximum temperatures:-


Any significant differences which are present can properly be attributed to a) the differences between mercury thermometers and platinum resistance thermometers, not, as you indicated between wooden and plastic screens, and that would probably be due to Mercury actually failing to capture the highest temperature, rather than exaggerating it, and b) the circulation of air around the screen.

How the Met Office currently reads temperatures

The Met Office has cast no doubt on the recorded extremes, and I've no reason to question that position.

That report isn't considering differences between wooden and plastic screens but it doesn't matter because the differences are small, and I said so at the outset. The problem is that both types of naturally ventilated louvred screens can read significantly higher than the true air temperature due mainly to strong solar radiation at low wind speeds. The Met Office continue using them in order to maintain continuity and comparability of records, which is as good a reason as any.


That report considers only night time temperatures in the Discussion and Conclusion sections, because that's when low wind speeds more often occur.

The main problem is that stations around the world - and for all I know in the UK too (though maybe not in the official, increasingly smaller, network) - are increasingly adopting more accurate (in strong sunshine etc.) aspirated screens and they don't appear to be affected as much by solar radiation at low wind speeds. The converse applies to a lesser extent, on clear calm nights.

I agree and that's pretty much what I said (i.e. plastic screens are only slightly better - not significantly better - than wooden).

The extra things might be more buildings on the Heathrow site for example these days, lowering screen height wind speeds a bit; more tarmac and concrete, fewer stevenson screen sites around than there used to be, and increasing use of accurate aspirated screens at least in some countries, making it more likely for the remaining stevenson screen sites to hit area records more often than they used to and less likely for aspirated sites to break records.

I stand by the 2 degrees C 'errors' seen occasionally in stevenson screens - from the same report:

But as long as all these known differences can be accurately compensated for, and if this is done, there may not be a problem.

You were saying though, that a problem existed in the last century due to wooden screens, as though what is currently used by the UK Met Office is superior, whereas we already know that the plastic screens they now use, differ little in temperature from the wooden ones, and as admitted by you, they will still use the screen for consistency.

As long as that consistency is maintained, then we in the UK are comparing like with like in terms of temperature records, notwithstanding that the aspirated system might be different.

That's really all we need to know.

What I said was " Many of these worldwide are slowly being replaced by better screen designs such as, for example, aspirated automatic weather station screens and even passive plastic screens are a bit 'better', so records aren't always directly comparable with the olden days."

It is modern professional aspirated designs that can introduce significant differences (the 'up to 2 deg C), they are coming increasingly into use in some countries - probably here too at some point (even I have one!). That's when records may be or become not directly comparable. Plastic screens are a 'bit better' than wood but they aren't the problem as the 'bit' is within acceptable tolerances. My post isn't about plastic versus wood, it's about different screen types versus the true air temperature, which professional aspirated screens are best able to reveal in certain conditions.

Yes the differences can be overcome when screens are changed (to aspirated ones) but only if there is a significant period of parallel running at those sites and I'm sure the Met Office would do this. Not so sure about some other countries though.

Although whatever the arguments concerning aspirated designs, they're all moot as the Met Office have no plans to change the screens they currently have in place. Ergo: like for like UK extremes will still be directly comparable.

True (although the one minute measurement frequency used at Heathrow tends to push up maxima slightly) but I mentioned worldwide as there was some discussion about Libya and Death Valley. They seem to be very keen on aspiration over in the USA so I wondered if that might be a factor in the persistence of that long standing record.

BAD NEWS .... for those seeking more summery conditions.

its all going pete tongue

low pressure is set to become dominant again as the azores high draws back thus relinquishing its influence on the uk. a strong high over newfoundland/greenland diverts the jet stream on a more southerly track - right across the uk.

so after a pleasant summery week, we are set to return to the preceeding dull rather wet conditions we endured since the end of the first week in june.

any chances now of a decent lengthy settled sunny spell this summer have all but gone.

we will problably get one in bloody september grrrr .... sod september thats autumn.

Its almost 9am and I have the lights on here in N.I, Its so dark and gloomy looking, slight drizzle, more like a morning in November than July.

That's true, although the jet stream is very weak at the moment, so it may not be too bad.

Aww, I love an Indian summer. And we've got some time off work in September.

Top temperature yesterday of 29 degrees in Northolt. Whilsts it still warm in London, its clouded over. Looks like the warm and sunny week we have just had is coming to an end.

indian summers or autumnal settled spells are pleasant and preferable to wind and rain. but imho they dont compare to a proper summer spell june/july when the days are long, the sun is high and everythings fresh, green and in full flower.

Can still be very warm in September, but the Sun is distinctly weaker than a month before.

End of July beginning of August, is usually the hottest part of the Summer - when conditions are right, of course

Hotness is overrated! Give me 20 to 23 degrees any day of the year. Like today (here S Hants). Sunny intervals and pleasant, heck you can even work in it.

heat in september is like snow in march.... pretty useless!


yer wuss! i worked out in 75, 76, 83, 90, 95, etc..... heat? bring it on! i can take it!

might get another mini heatwave into august.... looks like pressure might build over france and with that there and the uk under a mean upper flow from the southwest a transitory heatwave is possible.

Cant get enthusiastic about the weather when its dull and miserable and its supposed to be summer

What do you expect if you live in Katmandoodieland?

A heatwave is always possible as forecasts beyond 5 days are *still* unreliable. Heck you've already changed your tone only a day after your doom and gloom post - don't believe all that you see in the computer forecast models, they are usually no'but a rough guide beyond 5 days and sometimes less than that!

the noaa anomaly charts though are reliable in spotting the mean upper pattern when consistent. my doom and gloom post was a little hasty as the anomalies where readjusting so were not consistent.

they are consistent now, and suggest high pressure to our south over france by the end of next week.... however because the upper flow is still westerly/southwesterly its looking unsettled with transitory ridges possibly bringing a mini heatwave. there is no sign of a spell lasting more then 3 days though, and anything hot might only be 1 day, away from the favoured southeast.

a heatwave isnt possible if the anomaly charts arent suggesting a pattern thatll allow one , and all thats currently on offer sometime later next week if a transitory day or two.

WMO examines reported record temperature of 54°C in Kuwait



http://public.wmo.int/en/media/news/...%C2%B0c-kuwait