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]

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

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

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

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

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]

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.

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]

"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)
---------------------------------------------

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!)