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