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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#11
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On Monday, 10 July 2017 17:14:46 UTC+1, wrote:
On Mon, 10 Jul 2017 08:35:41 -0700 (PDT) Freddie wrote: On Monday, 10 July 2017 15:34:24 UTC+1, Graham P Davis wrote: On 09/07/17 19:44, Norman Lynagh wrote: Graham P Davis wrote: On 09/07/17 13:18, Ron Button wrote: The old scientific law of "what goes up must come down" was used to explain how at least half the sky would be be cloud-free due to the descending air The descending air doesn't necessarily occur in the vicinity of the cloud formed by the ascent of the air, though. I used this argument when I was being trained, but was told to carry on using the rule of thumb (I didn't!). I can see the logic behind what you are saying, but I would argue that it only applies to cumulus of limited vertical and horizontal extent - which is probably more often than not. I can't see any problem with reporting 8/8 Cu, but I would expect to only do it when the air was unstable to some depth, and I would expect to be reporting precipitation at the same time. As a fully trained observer I'm one of those too :-) 8/8 Cu and raining would normally be reported as 8/8 St or 8/8 Ns. Actually 8/8 Cu would be a sockiing big Cu If you saw it coming and your celestial dome was limited I would say report it. |
#12
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On a more general note, I am glad I am not the only one having problems with recording cloud cover, even after 30 years experience. The skies are always more complicated than the examples you find in books and on the web. Here at least (and I assume there is little special about Dundee) most mornings there's a mixture of types of cloud at different levels. There are gaps of different sizes all over the place, and I find estimating the cover on that basis very difficult. I might decide 4/8, but it could well be ⅝.. Am I missing something basic?
And then the patterns is often fast changing, so it might be 4/8 at 9.00, but could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't fully capture the picture. I realise one has to make a cutoff at some point. Of course this is all probably just a bit of noise in a set of records no one is ever going to use. Trevor Back from the Deep South of London and Devon where it was HOT to Dundee where it is COLD |
#13
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Trevor Harley wrote:
On a more general note, I am glad I am not the only one having problems with recording cloud cover, even after 30 years experience. The skies are always more complicated than the examples you find in books and on the web. Here at least (and I assume there is little special about Dundee) most mornings there's a mixture of types of cloud at different levels. There are gaps of different sizes all over the place, and I find estimating the cover on that basis very difficult. I might decide 4/8, but it could well be ⅝. Am I missing something basic? And then the patterns is often fast changing, so it might be 4/8 at 9.00, but could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't fully capture the picture. I realise one has to make a cutoff at some point. Of course this is all probably just a bit of noise in a set of records no one is ever going to use. Trevor Back from the Deep South of London and Devon where it was HOT to Dundee where it is COLD You make a very good point, Trevor. 'Observing' the weather is pretty much a full time job. 'Reporting' the weather by means of SYNOP or METAR observations is, as you say, merely capturing a snapshot at a moment in time which may, or may not, be representative of the weather experienced over a period of time. In my time working in the Met Office at Prestwick Airport in the 1960s during spells of bad weather ('bad' in the context of aircraft operations) we switched to so-called 'double observing'. One observer was continually outside on the balcony observing and recording the changes as they happened and passing this information to the other observer who was in the observing office. The person indoors was responsible for communicating the ever-changing information to ATC and other interested parties. He also kept all the formal logging and associated paperwork up to date. 'Observing' the weather at such times therefore employed 2 people continuously. The bean counters would never allow that today :-( -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l. http://peakdistrictweather.org Twitter: @TideswellWeathr |
#14
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On 11/07/17 09:19, Norman Lynagh wrote:
Trevor Harley wrote: On a more general note, I am glad I am not the only one having problems with recording cloud cover, even after 30 years experience. The skies are always more complicated than the examples you find in books and on the web. Here at least (and I assume there is little special about Dundee) most mornings there's a mixture of types of cloud at different levels. There are gaps of different sizes all over the place, and I find estimating the cover on that basis very difficult. I might decide 4/8, but it could well be ⅝. Am I missing something basic? And then the patterns is often fast changing, so it might be 4/8 at 9.00, but could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't fully capture the picture. I realise one has to make a cutoff at some point. Of course this is all probably just a bit of noise in a set of records no one is ever going to use. Trevor Back from the Deep South of London and Devon where it was HOT to Dundee where it is COLD You make a very good point, Trevor. 'Observing' the weather is pretty much a full time job. 'Reporting' the weather by means of SYNOP or METAR observations is, as you say, merely capturing a snapshot at a moment in time which may, or may not, be representative of the weather experienced over a period of time. In my time working in the Met Office at Prestwick Airport in the 1960s during spells of bad weather ('bad' in the context of aircraft operations) we switched to so-called 'double observing'. One observer was continually outside on the balcony observing and recording the changes as they happened and passing this information to the other observer who was in the observing office. The person indoors was responsible for communicating the ever-changing information to ATC and other interested parties. He also kept all the formal logging and associated paperwork up to date. 'Observing' the weather at such times therefore employed 2 people continuously. The bean counters would never allow that today :-( Reminds me of a couple of occasions as a forecaster when I'd torn a few strips off the DOF for criticising our observer. One was at Wethersfield when he complained that the last report was out of date and I pointed out that the observer had to run up several flights outside the tower to get a decent view of the visibility (the tower was in a hollow!) and that he'd already made seven special reports so far that hour. Another time was back at home base, Wattisham, when the DOF complained that we should have issued a special for the visibility having dropped below 3700M as he couldn't see the radio mast at that distance. I pointed out to him that the mast was actually at 4500M (figures may not be entirely accurate - this was about forty years ago) and that I could see it perfectly clearly through a couple of panes of glass. I wasn't sure whether his eyesight was failing - highly unlikely - or he just wanted an excuse to stop flying for the day. As to observing being a full-time job, I agree that it should be but I've known a few observers who boasted about how it only took 5 minutes an hour. Not a clever thing to say when staffing is being assessed. A quick look at the sky once - or perhaps twice - can lead you to misconceptions as to what's going on up there. One day, I was looking out of the printer-room window and I spent a while on it as I was a bit puzzled by what I was looking at. The observer returned from doing the ob and remarked that he was also a little baffled by what was up there but reckoned there was Sc at 4,000ft with some Ac, Cc, and Cs above. To be fair to him, for that ob, all the other stations in East Anglia were to report much the same assortment of clouds. As he'd started the ob early, I asked him to stand with me in the printer room and watch the cloud for a little while. It didn't take long before he burst out, "it's all the same cloud!" He then correctly sent out the ob with something like 5/8 Sc at 4,000ft and nothing above; all the other layers were simply the edge of the Sc where it gradually thinned and elements grew smaller towards the edge, first resembling Ac, then ripples like wind-blown sand typical of Cc, and finally a milky sheet he'd thought was Cs. Then there was the time at Wethersfield where I popped outside to do an ob and was surprised to see 7/8 CuSc at about 3,000 and 5,000ft where there'd been 8/8 St 200 and 400ft. Back inside, the CBR was still saying it was St and nothing else. Back outside, I stared for several minutes watching for wisps of St below the CuSc but there was nothing visible against the cloud or the numerous gaps of clear, blue sky. Then I saw the CuSc metamorphose back into St and the visibility plummet from tens of miles to less than a couple. Another example of how the small size of the elements of the CuSc had totally misled me regarding its height. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ “Like sewage, smartphones, and Donald Trump, some things are just inevitable.” [The Doctor] |