Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: cloud cover

  1. #1
    Join Date
    Jan 2014
    Posts
    228
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Default cloud cover

    Hi,

    somewhere I have read before how the cloud cover is defined using the measures like 10/10 etc.

    Can anybody explain it to me? I cannot find my earlier source. Sometimes I have not the correct english word for a good search in google ...

    Thanks.

    Marcel

  2. #2
    Join Date
    Nov 2007
    Location
    Wiltshire
    Posts
    2,497
    Thanks
    0
    Thanked 2 Times in 2 Posts

    Default

    Marcel,

    This is an indication of how much cloud cover there by considering the sky in tenmths. Thus 1/10 means only a small amount (trace) of cloud, 5/10 means half the sky is covered, and 10/10 means total cover (no sky visible). These days we use oktas (eigths), thus 1/8 is just a small amount (trace of cloud), 4/8 means half the sky is covered and 8/8 is total cover.

    Brian

  3. #3
    Join Date
    Aug 2011
    Posts
    1,716
    Thanks
    0
    Thanked 5 Times in 5 Posts

    Default

    Brian

    Was the cloud height used as a factor when planning operations?

    Regards

    Pete
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

  4. #4
    Join Date
    Nov 2007
    Location
    Wiltshire
    Posts
    2,497
    Thanks
    0
    Thanked 2 Times in 2 Posts

    Default

    I have to pass on that, Pete. Thinking about it logically, however, I think it would very much depend on the type of operation and whether you are referring to cloud base or cloud tops. Considering Bomber Command, for example, if thick cloud (in terms of difference between cloud base and top) was expected along the route and covering the target enveloped the planned operational height, then I suspect this would be taken into consideration. On the other hand I suspect that observed and forecast (for the planned return time) very low cloud at base airfields would not necessarily be considered a reason for cancelling a sortie - provided suitable diversion airfields were available.

    Thinking about ground-attack operations I suspect that the cloud base over a target area would be a major consideration as the attacking pilots would need time for target acquistion.

    I think it should also be recognised that in many cases of very low cloud the surface visibility is usually very poor, and that might be more of a consideration - although I appreciate there are many tales of aircraft returning to base in exceptionally poor conditions (a combination of low cloud and fog).

    So I don't know the official approach, but I hope the above might provide food for thought.

    Brian
    Last edited by Lyffe; 15th December 2015 at 18:36.

  5. #5
    Join Date
    Nov 2007
    Location
    Reading, Berkshire, UK
    Posts
    3,535
    Thanks
    3
    Thanked 11 Times in 11 Posts

    Default

    Marcel/Pete,
    Just to bring this up to date with regard to operational meteorology, there are magic programs called TDAs (Tactical Decision Aids). The Operators say what their weather limits (vis, wind speed/direction, cloud height/type/amount, rainfall, temperature, humidity, sea wave/swell, etc, etc,) are for any type of operation. The Meteorologists (or, these days, their computers!) then input their parameters, and the results – for whatever aspect of any operation - come out as Red (can’t be done), Yellow (marginal), or Green (do it!). In WW2 the BC Ops Research Branch was beginning to work towards this – but they didn’t have Excel spreadsheets!!! We used this latter to do all sorts of things from “AFV ‘going’” to Para DZ conditions, to FGA, or Recce. But even nowadays the commander of any Op is going to confront the Met Officer and say “Is it going to do THIS, or THAT?”. Decision time!!!! Waffling about "Maybe, but in places at times" is not what the military want to hear - but meteorology, in very small locations, and over very small time-scales is still, regretfully, an inexact science!
    HTH
    Peter Davies
    Meteorology is a science; good meteorology is an art!
    We might not know - but we might know who does!

  6. #6
    Join Date
    Jan 2014
    Posts
    228
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Default

    Hi,

    thanks for your replies, especially the one of Peter. I will have a further look into that matter.

    Marcel

  7. #7
    Join Date
    Jan 2014
    Posts
    228
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Default

    Although it is not a 70 year old information, this is a hint to what is meant:

    SKY CONDITION (from NWS, Media Guide to National Weather Service Terminology, 1996) Sky Condition Cloud Coverage:

    Cloudy 9/10 to 10/10 of the sky covered by clouds
    Mostly cloudy, or Considerable cloudiness 7/10 to 8/10
    Partly cloudy or Partly sunny 3/10 to 6/10
    Mostly clear or Mostly sunny 1/10 to 3/10

    Fair Less than 4/10 cloud cover, no precipitation Generally pleasant weather conditions

    Source:

    Marcel
    Last edited by Marcel L.; 15th December 2015 at 20:48.

  8. #8
    Join Date
    Nov 2007
    Location
    Wiltshire
    Posts
    2,497
    Thanks
    0
    Thanked 2 Times in 2 Posts

    Default

    Which is basically how I answered your question, except I gave the two extremes plus one in the middle. If you consider the sky as a circle bounded by the horizon, the the fraction, be it in tenths or oktas, is the amount of sky covered by cloud. However, you can have more than one layer of cloud, so an observation might be 2/10 at 1000 ft and 5/10 at 5000 ft; or 6/10 at 7000 ft and 5/10 at 25000 ft.

    The fraction refers to cloud cover - not the weather.

    Brian (retired forecaster)

  9. #9
    Join Date
    Jan 2014
    Posts
    228
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Default

    Hi,

    sure that is bascially what you have written Brian, thanks for your explanations. I just have found that in the internet and wanted to post it too. It is good to read the text from a real pro, thanks Brian.

    Marcel

  10. #10
    Join Date
    Aug 2011
    Posts
    1,716
    Thanks
    0
    Thanked 5 Times in 5 Posts

    Default

    Brian

    A section on meteorology in "Aircrew Lecture Notes" refers to the "standard weather code" which shows a scale of 0-9.

    The section reads:

    The cloud watcher notes how many tenths of the sky are covered with each kind of cloud. Thus if the sky is entirely covered with stratus, he notes stratus 10 tenths. If the sky is half covered with cumulus, he notes cumulus 5 tenths.

    Cloud amounts in forecasts are expressed in the same way.

    For reporting in the standard weather code, cloud amounts are converted by the following scale:

    0 = clear
    1 = trace of cloud
    2 = 1/10
    3 = 2/10 to 3/10
    4 = 4/10 to 6/10
    5 = 7/10 to 8/10
    6 = 9/10
    7 = over 9/10 but below 10/10
    8 = 10/10
    9 = sky obscured by fog
    Are you able to enlighten us on when this standard was introduced and/or provide any further detail on its usage?

    Regards

    Pete
    Last edited by PeteT; 16th December 2015 at 09:19. Reason: To include the complete text wording from the document
    Main areas of research:

    - CA Butler and the loss of Lancaster ME334 (http://rafww2butler.wordpress.com/ )
    - Aircrew Training (Basic / Trade / Operational / Continuation / Conversion)
    - The History of No. 35 Squadron (1916 - 1982) (https://35squadron.wordpress.com/)

    [Always looking for copies of original documents / photographs etc relating to these subjects]

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •