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Weather Watching - Enthusiasts Thread |
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#826 |
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Join Date: Feb 2004
Location: Southern East Anglia
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The June record nearly went last year though, with Heathrow surpassing the Southampton record for June of 35.6 ... on July 1st! There's a lot of luck involved in getting high temperature records late in May or June, or early in September or October but one by one, slowly but surely, the records will tumble.
Part of the problem is the use of old style passive louvred wooden screens in the last Century, these (including Stevenson screens) are known to produce artificially high air temperatures by up to 2 degrees C or so, sometimes more, in conditions of hot sunny weather with light winds. 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. link Quote:
For the last 20 to 30 years air temperature has been measured electronically using platinum resistance thermometers, high precision instruments accurate to within a hundredth of a degree. Before then mercury thermometers were read at set times by trained meteorological observers.
A measurement of air temperature is only meaningful if it is made consistently from site to site in a way that ensures that sunlight and rain do not interfere. For this reason the thermometer is housed in a Stevenson screen which allows the free circulation of air while excluding the weather elements. Stevenson lived over a hundred years ago and screens have been used to his original design ever since. In recent times it was decided to construct the screen in plastic rather than wood, to achieve better long term wear. To investigate what effect, if any, such a change might have on the temperature measurement, a year long trial was conducted comparing measurements from the different screens sited two metres apart. Mean temperature differences were less than 0.05 °C over the whole period. |
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#827 |
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Join Date: Oct 2010
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I've long believed the world record temperature to be 58c way back in 1922 in Libya, according to my old Guinness Record books. However it seems that this was recently disqualified and the new highest is 56.7c at Death Valley, California in 1913.
With so much said about globally rising temperatures, and June 2016 was apparently the hottest month ever globally, yet again, but Death Valley hasn't managed to surpass its highest temperature from over a century ago yet. Just saying! |
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#828 |
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Join Date: Dec 2004
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A lot of people think that 56.7C in Death Valley is wrong and likely some kind of recording error.
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. |
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#829 |
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Join Date: Oct 2003
Location: Darn Sarf
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Although the Met Office say that the net differences are in the order of < 0.05C.
link 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) Quote:
The naturally ventilated double-louvred Stevenson screen is a long-established design of thermometer shelter (e.g. Bilham, 1937), but even with such screens, their internal temperature may differ from air temperature by extremes of -0.5C to 2.5C (WMO,1983).
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.
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#830 |
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Join Date: Feb 2004
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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. 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:- Quote:
5. Conclusions 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. For the majority of the measurements considered here, the screen temperature and open-air fine-wire thermometer temperature agree closely, to a median difference <0.05◦C. However, larger temperature differences do occasionally occur, often at low (u2 < 1ms−1) wind speeds, for which thermometer screen properties are not reliably characterised. Low wind speeds are particularly common around the minimum of the diurnal cycle in temperature, and therefore the daily minimum temperature is likely to be the most badly affected of the maximum, minimum and 0900 UTC temperature measurements. This is unfortunate, as the daily minimum temperature is also often used in the ‘bi-mean’ method to calculate the daily average temperature, in combination with the daily maximum temperature. Such a procedure to determine the daily average will carry forward the daily minimum measurement vulnerable to ventilation errors. The results obtained here are specific to the measurement site at Reading. Whilst they will not be representative of all sites globally, they are probably unlikely to be entirely atypical of semi-urban sites in the United Kingdom, in terms of the diurnal cycle of thermometer screen ventilation, or in the year-to-year variability in calm periods arising from different circulation patterns. Consequently the 0900 UTC measurement may also provide a temperature observation at other sites which is less affected by poor ventilation than the daily minimum, although the overall prevalence of natural ventilation effects on screen temperature measurements seems unlikely to remain constant with time. 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. |
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#831 |
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Join Date: Oct 2003
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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.
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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 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. Quote:
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. 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: Quote:
Using an aspirated psychrometer to determine T air in three years of measurements at Kew Observatory, Painter (1977) found T air and T scrn differences for a large thermometer screen of up to 2C, which suggests a worst-case temperature excess in the United Kingdom of 2.5C (HMSO, 1981). These differences varied with wind speed and direction, and were attributed to response time and solar radiation effects.
But as long as all these known differences can be accurately compensated for, and if this is done, there may not be a problem.
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#832 |
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Join Date: Feb 2004
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Part of the problem is the use of old style passive louvred wooden screens in the last Century, these (including Stevenson screens) are known to produce artificially high air temperatures by up to 2 degrees C or so, sometimes more, in conditions of hot sunny weather with light winds.
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. |
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#833 |
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Join Date: Oct 2003
Location: Darn Sarf
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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. 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. |
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#834 |
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Join Date: Feb 2004
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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. |
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#835 |
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Join Date: Oct 2003
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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.
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#836 |
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Join Date: Oct 2005
Location: derby
Posts: 14,740
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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. |
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#837 |
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Join Date: Dec 2014
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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.
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#838 |
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Join Date: Feb 2004
Location: Southern East Anglia
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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. |
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#839 |
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Join Date: Nov 2012
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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. |
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#840 |
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Join Date: Jul 2003
Location: Pimlico, central London, UK
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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.
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#841 |
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Join Date: Oct 2005
Location: derby
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Aww, I love an Indian summer. And we've got some time off work in September.
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#842 |
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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.
End of July beginning of August, is usually the hottest part of the Summer - when conditions are right, of course
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#843 |
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Join Date: Oct 2003
Location: Darn Sarf
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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.
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#844 |
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Join Date: Oct 2005
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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 ![]() Quote:
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.
![]() i worked out in 75, 76, 83, 90, 95, etc..... heat? bring it on! i can take it!
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#845 |
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Join Date: Oct 2005
Location: derby
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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.
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#846 |
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Join Date: May 2005
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Cant get enthusiastic about the weather when its dull and miserable and its supposed to be summer
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#847 |
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Join Date: May 2009
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Cant get enthusiastic about the weather when its dull and miserable and its supposed to be summer
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#848 |
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Join Date: Oct 2003
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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.
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#849 |
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Join Date: Oct 2005
Location: derby
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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!
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. |
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#850 |
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Join Date: Oct 2010
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WMO examines reported record temperature of 54°C in Kuwait
http://public.wmo.int/en/media/news/...%C2%B0c-kuwait |
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i worked out in 75, 76, 83, 90, 95, etc..... heat? bring it on! i can take it!