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Unusual cloud 10th Oct15 - an analysis
On the 10th October 2016 a sheet of stratiform cloud was producing
fall-streak holes over southern UK. Howerver, holes developed in certain parts of the sheet only. An analysis of the available data indicates that the cloud was at a height near 25000 ft, and at a temperature of -31 C, and its unusually cold temperature holds the key to the unusual nature of this cloud. http://www.woksat.info/wwp/cloud-161010-final.pdf -- Bernard Burton Satellite images and weather data for Wokingham at: www.woksat.info/wwp.html --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
Unusual cloud 10th Oct15 - an analysis
On Tue, 25 Oct 2016 18:32:39 -0000
"Bernard Burton" wrote: On the 10th October 2016 a sheet of stratiform cloud was producing fall-streak holes over southern UK. Howerver, holes developed in certain parts of the sheet only. An analysis of the available data indicates that the cloud was at a height near 25000 ft, and at a temperature of -31 C, and its unusually cold temperature holds the key to the unusual nature of this cloud. http://www.woksat.info/wwp/cloud-161010-final.pdf Just had a quick glance through [I'll take a longer look tomorrow] but the idea that -31C is unusually low for water droplets to occur in clouds surprised me a bit. Nearly fifty years ago, I read that a research aircraft had found water droplets at a temperature of -60C. Just as a switch, I've also seen ice-crystal cloud (Ci Spi) seem to turn into water-droplet cloud but that's another story. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] |
Unusual cloud 10th Oct15 - an analysis
On Tuesday, 25 October 2016 21:44:56 UTC+1, Graham P Davis wrote:
On Tue, 25 Oct 2016 18:32:39 -0000 "Bernard Burton" wrote: On the 10th October 2016 a sheet of stratiform cloud was producing fall-streak holes over southern UK. Howerver, holes developed in certain parts of the sheet only. An analysis of the available data indicates that the cloud was at a height near 25000 ft, and at a temperature of -31 C, and its unusually cold temperature holds the key to the unusual nature of this cloud. http://www.woksat.info/wwp/cloud-161010-final.pdf Just had a quick glance through [I'll take a longer look tomorrow] but the idea that -31C is unusually low for water droplets to occur in clouds surprised me a bit. Nearly fifty years ago, I read that a research aircraft had found water droplets at a temperature of -60C. Just as a switch, I've also seen ice-crystal cloud (Ci Spi) seem to turn into water-droplet cloud but that's another story. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ Observation. The cloud consisted of 2 okta of a thin sheet of what looked at first sight to be high altocumulus stratiformis undulatus translucidus, but had a rather odd dull appearance, with a complete absence of the brightness normally associated with a water cloud. The colour was an almost uniform grey, with an absence of any shadowing. This cloud sheet had an edge to the SW, and seemed to be extensive beyond this edge. So who of us is allowed wild guesses experts ot inept? For me if the ice was on point of formation the crystals would have been stratified diferently to a set formation. 25 thousand is about the height of crystalisation isn't it? Would the optic been of a polarised sheet? If so you were seeing a snow cloud forming. But you should know that? many of these patches have a similar orientation and shape, aligned roughly W-E. Interestingly, what can also be seen are a number of cloud holes, most evident over the English Channel SE of the Isle of Wight. These have the appearance of fall-streak holes that can form when there is a thin layer of super-cooled water cloud, indicating an atmospheric layer saturated with respect to water, and super-saturated with respect to ice. Surely as ice forms it falls straight away isn't this what ammatus is all about?they are the nest thing to downdraughts are they not? Of the sort that throws aircraft around? |
Unusual cloud 10th Oct15 - an analysis
"Graham P Davis" wrote in message
-jade... On Tue, 25 Oct 2016 18:32:39 -0000 "Bernard Burton" wrote: On the 10th October 2016 a sheet of stratiform cloud was producing fall-streak holes over southern UK. Howerver, holes developed in certain parts of the sheet only. An analysis of the available data indicates that the cloud was at a height near 25000 ft, and at a temperature of -31 C, and its unusually cold temperature holds the key to the unusual nature of this cloud. http://www.woksat.info/wwp/cloud-161010-final.pdf Just had a quick glance through [I'll take a longer look tomorrow] but the idea that -31C is unusually low for water droplets to occur in clouds surprised me a bit. Nearly fifty years ago, I read that a research aircraft had found water droplets at a temperature of -60C. Just as a switch, I've also seen ice-crystal cloud (Ci Spi) seem to turn into water-droplet cloud but that's another story. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] Thanks Graham. Incidentally, I did not intend to give the view that -31C is unusually low for water droplets in clouds - I am sure it is not. I think my thrust was that the phenomenon of fall-streak holes was, in my experience, rare at that sort of temperature. All the research into spontaneous nucleation (Mason and others) points to almost instaneous nucliation at -41C at surface pressure, and this falls to -35C or so higher in the troposphere. It is also dependant on droplet size, the temperature rising for increasing droplet size. Water clouds undoubtably do exist at temperatures below -30C, but it is possible that they are time limited before nucliation takes place. Supercooled water at -60C requires an exceptionally pure atmosphere, virtually devoid of ice nuclei. -- Bernard Burton Satellite images and weather data for Wokingham at: www.woksat.info/wwp.html --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
Unusual cloud 10th Oct15 - an analysis
Bernard
I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. |
Unusual cloud 10th Oct15 - an analysis
On Wed, 26 Oct 2016 00:37:16 -0700 (PDT)
xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote:
On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] The more things change the more are kept the same. Hillary for presidunce as it were. But in this instance I was thinking more along the lines of electronic spikes. |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote:
On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] Enormous rows (and crossing outs in red in the obs book) about when ST became SC, or whether it was type 6 or type 7 stratus at everywhere that I worked. I liked 1000-1200 feet as a demarcation point but others had stratus bases much higher just like the Irish, who I did hear couldn't report a shower without reporting a CB at one time - not checked lately! |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, 26 October 2016 11:02:33 UTC+1, xmetman wrote:
On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] Enormous rows (and crossing outs in red in the obs book) about when ST became SC, or whether it was type 6 or type 7 stratus at everywhere that I worked. I liked 1000-1200 feet as a demarcation point but others had stratus bases much higher just like the Irish, who I did hear couldn't report a shower without reporting a CB at one time - not checked lately! And then, 20 minutes later, the sun breaks through. |
Unusual cloud 10th Oct15 - an analysis
"xmetman" wrote in message ... On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. Yes 1000 feet was the de-facto St/Sc switch height when I was an observer. I remember once at Manby we had a morning when the duty observer night flying was reporting 2/8 stratus at 300 feet (estimated). Come soon after dawn it was apparent that said cloud was dense cirrus s****atus (type 2). It looked quite dark so I could see why the night-shift were misled. On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. Will -- " Some sects believe that the world was created 5000 years ago. Another sect believes that it was created in 1910 " http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm Will Hand (Haytor, Devon, 1017 feet asl) --------------------------------------------- |
Unusual cloud 10th Oct15 - an analysis
On Wed, 26 Oct 2016 11:43:59 +0100
"Eskimo Will" wrote: On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. I was told very early in my career that one should never report more than half-cover of Cu. I didn't agree at first but it was pointed out to me that one should judge the amount by only including the base of the cloud in one's estimation of the coverage; the sides of the cloud should always be counted as being part of the sky, not the cloud. When I applied that rule and mentally switched the sides of the cloud from yellow, say, to blue to match the sky, I don't remember ever having to report more than 4/8 of Cu. With cirrus being precipitation, should it be counted as a cloud? And if it is a cloud, isn't snow Cirrus? ;-) The same could be said of As since that is merely precipitation, perhaps with the Ac mother-cloud still in existence above it. Ever since I joined the Met Office, I've been tempted to report low-level Cirrus when I've had decaying snow showers drifting in from the North Sea and sometimes had half the sky covered with snow but no reportable clouds. Never had the guts to try it though; it would have been a waste of effort in any case. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] |
Unusual cloud 10th Oct15 - an analysis
Eskimo Will wrote:
"xmetman" wrote in message ... On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. Yes 1000 feet was the de-facto St/Sc switch height when I was an observer. I remember once at Manby we had a morning when the duty observer night flying was reporting 2/8 stratus at 300 feet (estimated). Come soon after dawn it was apparent that said cloud was dense cirrus s****atus (type 2). It looked quite dark so I could see why the night-shift were misled. On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. Will The height of the observing site is a factor as well. A Sc layer that's 1500 ft above sea level is only 500 ft above here but it's still Sc. The deciding factor is often whether or not the cloud has a well-defined base. If it has it's probably best described as Sc. If not, it's probably St. I appreciate that's broad generalisation but it's a good starting point. -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l. http://peakdistrictweather.org @TideswellWeathr |
Unusual cloud 10th Oct15 - an analysis
Graham P Davis wrote:
On Wed, 26 Oct 2016 11:43:59 +0100 "Eskimo Will" wrote: On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. I was told very early in my career that one should never report more than half-cover of Cu. I didn't agree at first but it was pointed out to me that one should judge the amount by only including the base of the cloud in one's estimation of the coverage; the sides of the cloud should always be counted as being part of the sky, not the cloud. When I applied that rule and mentally switched the sides of the cloud from yellow, say, to blue to match the sky, I don't remember ever having to report more than 4/8 of Cu. What would you report as the total cloud cover in that case? -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l. http://peakdistrictweather.org @TideswellWeathr |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, 26 October 2016 16:18:50 UTC+1, Graham P Davis wrote:
On Wed, 26 Oct 2016 11:43:59 +0100 "Eskimo Will" wrote: With cirrus being precipitation, should it be counted as a cloud? And if it is a cloud, isn't snow Cirrus? ;-) The same could be said of As since that is merely precipitation, perhaps with the Ac mother-cloud still in existence above it. Ever since I joined the Met Office, I've been tempted to report low-level Cirrus when I've had decaying snow showers drifting in from the North Sea and sometimes had half the sky covered with snow but no reportable clouds. Never had the guts to try it though; it would have been a waste of effort in any case. -- When I was in the UKMO old-timers who had spent a spell in Antarctica would mention diamond dust (ice fog) and considered it as cirrus on the deck. Whether the sparkly ice crystals were neutrally buoyant or fell down slowly they never said. It's true that typical mare's tails cirrus (s****atus?) seem very often to originate from something vaguely cumuliform and look like precipitation or virga. MartinR |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, October 26, 2016 at 4:37:14 PM UTC+1, Norman Lynagh wrote:
Eskimo Will wrote: "xmetman" wrote in message ... On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. Yes 1000 feet was the de-facto St/Sc switch height when I was an observer. I remember once at Manby we had a morning when the duty observer night flying was reporting 2/8 stratus at 300 feet (estimated). Come soon after dawn it was apparent that said cloud was dense cirrus s****atus (type 2). It looked quite dark so I could see why the night-shift were misled. On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. Will The height of the observing site is a factor as well. A Sc layer that's 1500 ft above sea level is only 500 ft above here but it's still Sc. The deciding factor is often whether or not the cloud has a well-defined base. If it has it's probably best described as Sc. If not, it's probably St. I appreciate that's broad generalisation but it's a good starting point. -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l. http://peakdistrictweather.org @TideswellWeathr I've got several 100 cloud photographs, all catalogued and arranged into types. Difficulties deciding the type means a quite a few are logged twice, under different types. It's good to see the 'professionals' also have problems. Perhaps I'll upload a few of the problem cases a try to get other opinions, which - going by the above, are likely to be varied! Graham Penzance Graham Penzance |
Unusual cloud 10th Oct15 - an analysis
On 26 Oct 2016 15:40:09 GMT
"Norman Lynagh" wrote: Graham P Davis wrote: On Wed, 26 Oct 2016 11:43:59 +0100 "Eskimo Will" wrote: On another note big arguments over whether 7/8 Cu should be reported or not when it was obvious large holes in the cloud field were apparent but little blue sky visible. Another sticky point was the under-estimating of cirrus amount, putting dark glasses on usually revealed much more than reported. I was told very early in my career that one should never report more than half-cover of Cu. I didn't agree at first but it was pointed out to me that one should judge the amount by only including the base of the cloud in one's estimation of the coverage; the sides of the cloud should always be counted as being part of the sky, not the cloud. When I applied that rule and mentally switched the sides of the cloud from yellow, say, to blue to match the sky, I don't remember ever having to report more than 4/8 of Cu. What would you report as the total cloud cover in that case? If the cumulus was the sole cloud, the total amount of cloud would be the same, 4 octas. -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] |
Unusual cloud 10th Oct15 - an analysis
On Wednesday, 26 October 2016 17:01:21 UTC+1, MartinR wrote:
On Wednesday, 26 October 2016 16:18:50 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 11:43:59 +0100 "Eskimo Will" wrote: With cirrus being precipitation, should it be counted as a cloud? And if it is a cloud, isn't snow Cirrus? ;-) The same could be said of As since that is merely precipitation, perhaps with the Ac mother-cloud still in existence above it. Ever since I joined the Met Office, I've been tempted to report low-level Cirrus when I've had decaying snow showers drifting in from the North Sea and sometimes had half the sky covered with snow but no reportable clouds. Never had the guts to try it though; it would have been a waste of effort in any case. -- When I was in the UKMO old-timers who had spent a spell in Antarctica would mention diamond dust (ice fog) and considered it as cirrus on the deck. Whether the sparkly ice crystals were neutrally buoyant or fell down slowly they never said. It's true that typical mare's tails cirrus (s****atus?) seem very often to originate from something vaguely cumuliform and look like precipitation or virga. MartinR I reported diamond dust at Kinloss around 25 years ago. It was obviously nowhere as cold as it gets in The Arctic, getting down to -10°C with shallow mist and patches of fog on a snow surface. I wouldn't have seen it (but I might have felt it) if ATC hadn't had their searchlight trained on me in the Met enclosure doing the 2100 observation! Its an effect that I suppose is very much like virga falling as ice crystals in cirrus, and probably happens a lot more widely than we imagine in the upper atmosphere. |
Unusual cloud 10th Oct15 - an analysis
On Wed, 26 Oct 2016 03:02:31 -0700 (PDT)
xmetman wrote: On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. Enormous rows (and crossing outs in red in the obs book) about when ST became SC, or whether it was type 6 or type 7 stratus at everywhere that I worked. I liked 1000-1200 feet as a demarcation point but others had stratus bases much higher just like the Irish, who I did hear couldn't report a shower without reporting a CB at one time - not checked lately! Yes, I was never too sure about that but the in the case I mentioned there was no doubt at all. The sky had changed from 8/8 St at 200 and 400ft with vis somewhere around a couple of Km to 7/8 Sc with 3/8 Cu below and vis over 20km. When I saw the CBR giving the same cloud base and cover as before, I assumed there must have been a very thin layer below the CuSc that I'd not noticed. I stared at the patches of blue sky but could see nothing below the CuSC. Then I saw the sharp edges of the clouds begin to blur and they suddenly lost their structure to become St and, at the same time, the vis dropped back to a couple of km. On another occasion years before at Bedford, the sky had resembled the type of St or Sc of which you speak; large rolls of ragged, black-based cloud resembling something at no more than a thousand feet. Trouble was, I knew it was neither type as I'd been watching it for a long time. An aircraft then reported the base at 25,000ft with top at 34,000. Would have caused a bit of a kerfuffle if I'd reported St or Sc at 25,000ft! ;-) -- Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer] Web-site: http://www.scarlet-jade.com/ There are more fools than knaves in the world, else the knaves would not have enough to live upon. [Samuel Butler] |
Unusual cloud 10th Oct15 - an analysis
"Graham P Davis" wrote in message -jade... On Wed, 26 Oct 2016 03:02:31 -0700 (PDT) xmetman wrote: On Wednesday, 26 October 2016 10:40:43 UTC+1, Graham P Davis wrote: On Wed, 26 Oct 2016 00:37:16 -0700 (PDT) xmetman wrote: Bernard I took photo's of the cloud edge when it first appeared that morning at about 0830 UTC and posted shortly after on the Weather Climate forum in an item that I called "Skies across the SW" https://groups.google.com/d/msg/weat...o/zFJtJn3oBQAJ I noticed the edge of what I thought was a high AC sheet as it moved down from the NW and pinpointed the edge on the visible satellite image for 0815 UTC. Unfortunately I didn't see any of the fallstreak holes which occurred further east. Looking back at the observation from the LCBR from the Exeter Airport AWS I can see that AC had a very high base indeed 23,000 feet! 03844 - Exeter Airport United Kingdom 31 M AMSL [50.7 N 3.4 W] AAXX 10154 03844 46784 /0503 10132 20047 30219 40252 57014 333 55300 20465 83/56== AAXX 10144 03844 46683 /0606 10133 20041 30225 40258 56016 333 55304 21099 87/44== AAXX 10134 03844 46683 /0306 10147 20044 30228 40261 58018 333 55310 21955 81/39== AAXX 10124 03844 16981 /0707 10137 20057 30234 40267 58013 69921 333 55310 21894== AAXX 10114 03844 46982 /0506 10129 20062 30241 40274 58003 333 55310 21699 81/73== AAXX 10104 03844 46978 /3302 10105 20078 30246 40279 56002 333 55302 20897 88/73== AAXX 10094 03844 46736 /1901 10091 20078 30247 40281 55000 333 55309 20930 81/56 87/73== AAXX 10084 03844 46767 /3502 10056 20055 30244 40278 58001 333 55310 20305 81/56== AAXX 10074 03844 46763 /0502 10036 20035 30248 40282 53001 333 55300 20015 87/56== AAXX 10064 03844 16761 /0602 10033 20031 30248 40282 54000 60002 333 20006 3/101 55088 55300 20000 70000 88/50== AAXX 10054 03844 46763 /3202 10012 20009 30245 40280 56005 333 55300 20000 83/50== AAXX 10044 03844 46959 /3503 10024 20021 30246 40281 56008 333 55300 20000== AAXX 10034 03844 46862 /0302 10028 20025 30248 40282 58008 333 55300 20000 81/57== AAXX 10024 03844 46860 /0402 10020 20018 30250 40284 58008 333 55300 20000 81/57== AAXX 10014 03844 46902 /0301 10025 20021 30254 40288 58004 333 55300 20000== AAXX 10004 03844 16860 /0202 10035 20030 30255 40290 58003 60001 333 55/// 21148 83/57== As an observer I still would have reported it as AC but with some exotic height of 16,000 feet or so. Bruce. Yes, one of the first problems I saw with the standard splitting of cloud levels into low, medium, and high was when I was on my Scientific Assistant course in September 1963. There was a fair amount of unstable Ac around one day which was being reported at anywhere between 10-15,000ft. This then precipitated out as ice crystals and the reports changed to Ci spi at 20,000ft. ;-) There were several occasions when I should have reported Ac or As as 25,000ft but chickened out as I knew it would trigger a row with Group or Bracknell. One time at wethersfield, I went out for the ob and saw that the St at 200 and 400ft had gone and been replaced by CuSc at what looked like 3,000 and 4,000ft. Checking with the CBR and looking outside again revealed that the CuSC was at the same height as the St had been. Can't remember what I reported but as I was older and more bolshie by that time, I hope I stuck to CuSC and 200 and 400ft. Since retiring, I have seen Cirrus with a base of 6,000ft (top 13,000ft) and associated halo. I bet I would have had a struggle getting such an ob past the powers-that-be in days of yore. Enormous rows (and crossing outs in red in the obs book) about when ST became SC, or whether it was type 6 or type 7 stratus at everywhere that I worked. I liked 1000-1200 feet as a demarcation point but others had stratus bases much higher just like the Irish, who I did hear couldn't report a shower without reporting a CB at one time - not checked lately! Yes, I was never too sure about that but the in the case I mentioned there was no doubt at all. The sky had changed from 8/8 St at 200 and 400ft with vis somewhere around a couple of Km to 7/8 Sc with 3/8 Cu below and vis over 20km. When I saw the CBR giving the same cloud base and cover as before, I assumed there must have been a very thin layer below the CuSc that I'd not noticed. I stared at the patches of blue sky but could see nothing below the CuSC. Then I saw the sharp edges of the clouds begin to blur and they suddenly lost their structure to become St and, at the same time, the vis dropped back to a couple of km. On another occasion years before at Bedford, the sky had resembled the type of St or Sc of which you speak; large rolls of ragged, black-based cloud resembling something at no more than a thousand feet. Trouble was, I knew it was neither type as I'd been watching it for a long time. An aircraft then reported the base at 25,000ft with top at 34,000. Would have caused a bit of a kerfuffle if I'd reported St or Sc at 25,000ft! ;-) On Dartmoor I have often seen cumulus with a base at around 500 feet or so. One day it was 8/8 (from my perspective) cumulus on the deck and snowing. I know it was cumulus because we walked into it! Will -- " Some sects believe that the world was created 5000 years ago. Another sect believes that it was created in 1910 " http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm Will Hand (Haytor, Devon, 1017 feet asl) --------------------------------------------- |
Unusual cloud 10th Oct15 - an analysis
In message ,
xmetman writes On Wednesday, 26 October 2016 17:01:21 UTC+1, MartinR wrote: When I was in the UKMO old-timers who had spent a spell in Antarctica would mention diamond dust (ice fog) and considered it as cirrus on the deck. Whether the sparkly ice crystals were neutrally buoyant or fell down slowly they never said. It's true that typical mare's tails cirrus (s****atus?) seem very often to originate from something vaguely cumuliform and look like precipitation or virga. MartinR I reported diamond dust at Kinloss around 25 years ago. It was obviously nowhere as cold as it gets in The Arctic, getting down to -10°C with shallow mist and patches of fog on a snow surface. I wouldn't have seen it (but I might have felt it) if ATC hadn't had their searchlight trained on me in the Met enclosure doing the 2100 observation! Its an effect that I suppose is very much like virga falling as ice crystals in cirrus, and probably happens a lot more widely than we imagine in the upper atmosphere. I believe I once experienced diamond dust here in Cranleigh, one exceptionally cold early morning when the temperature was -13 or so. It's so long ago that I'm not quite sure when it was. It could have been February 1986 or it might have been 1963. -- John Hall "One can certainly imagine the myriad of uses for a hand-held iguana maker" Hobbes (the tiger, not the philosopher!) |
Unusual cloud 10th Oct15 - an analysis
This has been an interesting topic. I have over thirty years observing experience and can relate to some of the comments but not to others. I would say that whether you call a cloud St or Sc is related to the height of the cloud and visible structure of the same. The same Sc at, say, 2500ft observed from sea level would be St 2400ft up the mountain as any hill walker would know. I've reported Cu at 7000ft and had a glider pilot tell me that he was at 9000ft and the Cu base was above him. I was always happy to report high Ac at 18000ft if I felt that to be correct.
As observers (old style!) there were endless "discussion", in any office I served at, about all aspects of observing and I always looked at these as good learning opportunities. Some offices, however, were very set in their observing ways and didn't take kindly to new ideas. I'm intrigued at how Will can tell a cloud type when he's in it. Just hill fog, surely? |
Unusual cloud - and my analysis
On Thursday, 27 October 2016 13:53:38 UTC+1, Desperate Dan wrote:
This has been an interesting topic. I have over thirty years observing experience and can relate to some of the comments but not to others. Never give up on losers I always say, when I say that I would say that whether you call a cloud weather or not is related to the height of the cloud and visible structure of the same. (Among other things. But you all know what relations are like.) The same Sc at, say, 2500ft observed from sea level would be St 2400ft up the mountain as any hill walker would know. I've reported Cu at 7000ft and had a glider pilot tell me that he was at 9000ft and the Cu base was above him. I was always happy to report high Ac at 18000ft if I felt that to be correct. One has to imagine a fair few things with relations like that. As observers (old style!) there were endless "discussion", in any office I served at, about all aspects of observing and I always looked at these as good learning opportunities. You did? See what I mean about never giving up! Some offices, however, were very set in their observing ways and didn't take kindly to new ideas. I'm intrigued at how Will can tell a cloud type when he's in it. Just hill fog, surely? There's always yesterday's charts for the attentive to relate. Speaking of which: I was watching a big black cigar rolling by yesterday (well more grey but relatively dark as far as cloud relatives run.) Seeing as there is such a large anticyclone right in the middle of the Atlantic at the moment I wonder if it is worth stating the obvious relating to the dull overcast overhead at present. It would be a pity if very few were paying attention after all this talk around the station hearths. If there are no tinnitus sufferers here willing to discuss crickets in their belfies, perhaps some of the better mathematicians can point out to the rest of us what is wrong with this sequence: 24; 48; 72 and 120? https://weather.gc.ca/ensemble/naefs/cartes_e.html Good luck with that, children. |
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