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



---
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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]

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?

"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



---
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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.

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]

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.

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!

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.

"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)
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