Cloudbase in METARs

[MichaelJP59]

FEW005 SCT007 BKN009

This is from a METAR at LBA/EGNM today.

I believe they only detail the first 3 layers of cloud. But how can an observer at the field possibly come up with a sensible oktant estimate for 3 layers of cloud 200 feet apart as listed above?

Also, how would I know from that whether it is overcast above 900 feet? As this would obviously make a VFR flight impossible.

Thanks for any help.

[Genghis the Engineer]

No idea about the former, but you can fly VFR quite legally at 800ft so long as you stay below 140kn.

It may, depending upon terrain and your own experience not be very clever - but it's possible.

G

[FlyingForFun]

Best way of finding out what the actual weather is like above 900ft would be to phone Leeds ATC and ask them.

Not sure how Leeds measure their cloud-bases, but here at Blackpool it is done by a machine. The machine is known to not be totally accurate - it is located on top of a building, and can only detect clouds directly above that building. It has been known to report the clouds as BKN or even OVC when there is just one medium-sized cloud but this cloud happens to be sat on top of the building where the detector is. Because of this, ATC frequently amend the data from the machine based on pilot reports and occassionally on their own observations.

My best guess as to the actual weather at Leeds based on this METAR (since I haven't been anywhere near Leeds today) would be some type of cumuliform cloud, where the base is not constant. Some of the clouds extend down to 500ft, others only as low as 700ft, and others still only down as far as 900ft. So it's bsaically just one layer of cloud, with no cloud-free layers between 500 and 700 feet, nor between 700 and 900 feet. I wouldn't expect to see too many holes. But that is just a guess.

FFF
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[MichaelJP59]

> Best way of finding out what the actual
> weather is like above 900ft would be to
> phone Leeds ATC and ask them.

Which is what I ended up doing.

It does show the limitations of the METAR system though. It's difficult to think of a way of conveying more information without making the character string too long.

It would be nice to always have an overcast level though, if there is one, rather than 3 rather useless layers like in the example.