On Monday, 10 July 2017 17:14:46 UTC+1, wrote:
On Mon, 10 Jul 2017 08:35:41 -0700 (PDT)
Freddie wrote:

On Monday, 10 July 2017 15:34:24 UTC+1, Graham P Davis wrote:
On 09/07/17 19:44, Norman Lynagh wrote:
Graham P Davis wrote:

On 09/07/17 13:18, Ron Button wrote:
The old scientific law of "what
goes up must come down" was used to explain how at least half the sky
would be be cloud-free due to the descending air
The descending air doesn't necessarily occur in the vicinity of the cloud
formed by the ascent of the air, though. I used this argument when I was
being trained, but was told to carry on using the rule of thumb (I didn't!).
I can see the logic behind what you are saying, but I would argue that it
only applies to cumulus of limited vertical and horizontal extent - which is
probably more often than not. I can't see any problem with reporting 8/8 Cu,
but I would expect to only do it when the air was unstable to some depth, and
I would expect to be reporting precipitation at the same time.


As a fully trained observer
I'm one of those too :-)

8/8 Cu and raining would normally be reported as 8/8 St or 8/8
Ns. Actually 8/8 Cu would be a sockiing big Cu
If you saw it coming and your celestial dome was limited I would say report it.

On a more general note, I am glad I am not the only one having problems with recording cloud cover, even after 30 years experience. The skies are always more complicated than the examples you find in books and on the web. Here at least (and I assume there is little special about Dundee) most mornings there's a mixture of types of cloud at different levels. There are gaps of different sizes all over the place, and I find estimating the cover on that basis very difficult. I might decide 4/8, but it could well be â…�.. Am I missing something basic?

And then the patterns is often fast changing, so it might be 4/8 at 9.00, but could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't fully capture the picture. I realise one has to make a cutoff at some point.

Of course this is all probably just a bit of noise in a set of records no one is ever going to use.


Trevor
Back from the Deep South of London and Devon where it was HOT to Dundee where it is COLD

Trevor Harley wrote:

On a more general note, I am glad I am not the only one having problems with
recording cloud cover, even after 30 years experience. The skies are always
more complicated than the examples you find in books and on the web. Here at
least (and I assume there is little special about Dundee) most mornings
there's a mixture of types of cloud at different levels. There are gaps of
different sizes all over the place, and I find estimating the cover on that
basis very difficult. I might decide 4/8, but it could well be â…�. Am I
missing something basic?

And then the patterns is often fast changing, so it might be 4/8 at 9.00, but
could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't
fully capture the picture. I realise one has to make a cutoff at some point.

Of course this is all probably just a bit of noise in a set of records no one
is ever going to use.


Trevor
Back from the Deep South of London and Devon where it was HOT to Dundee where
it is COLD

You make a very good point, Trevor. 'Observing' the weather is pretty much a
full time job. 'Reporting' the weather by means of SYNOP or METAR observations
is, as you say, merely capturing a snapshot at a moment in time which may, or
may not, be representative of the weather experienced over a period of time.

In my time working in the Met Office at Prestwick Airport in the 1960s during
spells of bad weather ('bad' in the context of aircraft operations) we switched
to so-called 'double observing'. One observer was continually outside on the
balcony observing and recording the changes as they happened and passing this
information to the other observer who was in the observing office. The person
indoors was responsible for communicating the ever-changing information to ATC
and other interested parties. He also kept all the formal logging and
associated paperwork up to date. 'Observing' the weather at such times
therefore employed 2 people continuously. The bean counters would never allow
that today :-(

--
Norman Lynagh
Tideswell, Derbyshire
303m a.s.l.
http://peakdistrictweather.org
Twitter: @TideswellWeathr

On 11/07/17 09:19, Norman Lynagh wrote:
Trevor Harley wrote:

On a more general note, I am glad I am not the only one having problems with
recording cloud cover, even after 30 years experience. The skies are always
more complicated than the examples you find in books and on the web. Here at
least (and I assume there is little special about Dundee) most mornings
there's a mixture of types of cloud at different levels. There are gaps of
different sizes all over the place, and I find estimating the cover on that
basis very difficult. I might decide 4/8, but it could well be â…�. Am I
missing something basic?

And then the patterns is often fast changing, so it might be 4/8 at 9.00, but
could easily be 6/8 at 8.50 and 9.10, so recording a simple snapshot doesn't
fully capture the picture. I realise one has to make a cutoff at some point.

Of course this is all probably just a bit of noise in a set of records no one
is ever going to use.


Trevor
Back from the Deep South of London and Devon where it was HOT to Dundee where
it is COLD

You make a very good point, Trevor. 'Observing' the weather is pretty much a
full time job. 'Reporting' the weather by means of SYNOP or METAR observations
is, as you say, merely capturing a snapshot at a moment in time which may, or
may not, be representative of the weather experienced over a period of time.

In my time working in the Met Office at Prestwick Airport in the 1960s during
spells of bad weather ('bad' in the context of aircraft operations) we switched
to so-called 'double observing'. One observer was continually outside on the
balcony observing and recording the changes as they happened and passing this
information to the other observer who was in the observing office. The person
indoors was responsible for communicating the ever-changing information to ATC
and other interested parties. He also kept all the formal logging and
associated paperwork up to date. 'Observing' the weather at such times
therefore employed 2 people continuously. The bean counters would never allow
that today :-(


Reminds me of a couple of occasions as a forecaster when I'd torn a few
strips off the DOF for criticising our observer.

One was at Wethersfield when he complained that the last report was out
of date and I pointed out that the observer had to run up several
flights outside the tower to get a decent view of the visibility (the
tower was in a hollow!) and that he'd already made seven special reports
so far that hour.

Another time was back at home base, Wattisham, when the DOF complained
that we should have issued a special for the visibility having dropped
below 3700M as he couldn't see the radio mast at that distance. I
pointed out to him that the mast was actually at 4500M (figures may not
be entirely accurate - this was about forty years ago) and that I could
see it perfectly clearly through a couple of panes of glass. I wasn't
sure whether his eyesight was failing - highly unlikely - or he just
wanted an excuse to stop flying for the day.

As to observing being a full-time job, I agree that it should be but
I've known a few observers who boasted about how it only took 5 minutes
an hour. Not a clever thing to say when staffing is being assessed.

A quick look at the sky once - or perhaps twice - can lead you to
misconceptions as to what's going on up there. One day, I was looking
out of the printer-room window and I spent a while on it as I was a bit
puzzled by what I was looking at. The observer returned from doing the
ob and remarked that he was also a little baffled by what was up there
but reckoned there was Sc at 4,000ft with some Ac, Cc, and Cs above. To
be fair to him, for that ob, all the other stations in East Anglia were
to report much the same assortment of clouds. As he'd started the ob
early, I asked him to stand with me in the printer room and watch the
cloud for a little while. It didn't take long before he burst out, "it's
all the same cloud!" He then correctly sent out the ob with something
like 5/8 Sc at 4,000ft and nothing above; all the other layers were
simply the edge of the Sc where it gradually thinned and elements grew
smaller towards the edge, first resembling Ac, then ripples like
wind-blown sand typical of Cc, and finally a milky sheet he'd thought
was Cs.

Then there was the time at Wethersfield where I popped outside to do an
ob and was surprised to see 7/8 CuSc at about 3,000 and 5,000ft where
there'd been 8/8 St 200 and 400ft. Back inside, the CBR was still saying
it was St and nothing else. Back outside, I stared for several minutes
watching for wisps of St below the CuSc but there was nothing visible
against the cloud or the numerous gaps of clear, blue sky. Then I saw
the CuSc metamorphose back into St and the visibility plummet from tens
of miles to less than a couple. Another example of how the small size of
the elements of the CuSc had totally misled me regarding its height.

--
Graham P Davis, Bracknell, Berks. [Retd meteorologist/programmer]
Web-site: http://www.scarlet-jade.com/
“Like sewage, smartphones, and Donald Trump, some things are just
inevitable.� [The Doctor]