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stabell

A suggestion: Solving the cloud cover problem

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(I trust that this new version of Active Sky has solved the problem that earlier versions have had for some users: A metar calls for overcast, and the sky is still completely clear. This post is not about that early (?) problem).There is one problem, however, with the way FSX weather system/ActiveSky works. The problem is that the weather is based on METARs.I feel that the developers may not have understood what happens when Metar is the only source of weather-making.First problem example: An airport has cumulus clouds only, cloud base 2000 feet, stretches up to maybe 10000 feet. Reported as "BKN020"."Broken" means 5/8 to 7/8 of the sky covered. It seems to me that Microsoft has used 5/8 for "broken" instead of 6/8 and 7/8, making the cloud cover not-so-broken.I suppose ActiveSky cannot inject 6.3/8 or something, but only "BKN"? In that case there is nothing to do if Microsoft has defined BKN as 5/8, for example.But when people look out of the window and see a completely obscured sky, and start FSX/AS2012 and see large spots of blue skyt through the cloud cover, it can be caused by the fact that real cumulusclouds, while they stretch upwards, increase in size! They can look like cumulunimbus, in a smaller scale, so that when the clouds at the cloud base cover 5/8, they will come in touch with each other at thetops, making it cover the sky completely, so that you cannot see blue sky through it.My experience is that if a single thin layer of cloud (stratus) is reported as "BKN", then it will indeed look broken, both in real life and in FSX. So my first suggestion is to make all cumulus layers morecovered than the metar calls for, beacuse of the cumulus clouds tendency to grow in size upwards, and cover the blue sky, even if it is reported as BKN.Suggestion 1: Active Sky should have a user selectable option: "make FEW=SCT, make SCT=BKN, make BKN=OVC."But the main big issue when basing weather depiction upon Metar observation is caused by the Metar reporting system itself:* A Metar will not report a cloud layer if there is a more crowded cloud layer below. If we have BKN020 they will not report a SCT030.You can have FEW015 SCT020 BKN030, but for some reason you can not have BKN020 SCT030 SCT040..A typical weather situation in my part of Europe is warm frontal systems. Different to a cold front consting of basically one thick layer of cumulus/cumulunimbus, a warm frontal system can typically consist ofBKN020 BKN030 BKN080 BKN120 BKN200 ... and on the top OVC300 cirrus.When you start your descent you go into clouds, and sometimes on the way down you can see horisontally a long way (with clouds over and below), but basically ten thousand meters of clouds over theairport.The Metar says: BKN020, causing Active Sky to put one cumulus layer stretching from 2000 to 6000 feet, and big, blue holes to see the sun through. That metar is indeed the same as in a nice summerevening, when a thin stratus layer stretches red and orange over the evening sky, stretching from 2000 to 2500 feet. Metar: BKN020.In my opinion that is the reason for why so many people have complained about the weather depiction on the ActiveSky forums for so many years.Suggestion 2: Selectable option in AS2012: "if the metar says BKN or OVC, treat this as a big frontal weather system, and not as a single layer of clouds in an othewise nice weather situation. Add cloud layersappropriate for a typical frontal system: BKN020 becomes BKN020, BKN060 OVC100stratus OVC140Stratus.....OVC250 Cirrus". And important: This will apply for airports at least 100-200nm away, so if airportsalong your flight plan route is also reporting BKN105 -RA.., then the same weather should be applied there.I understand that AS2012 cannot guess if BKN020 means a single layer of stratus, or clouds stretching up to FL350. But you don't have to be a meteorologist to know that if precipitation is reported, it is nosingle, thin, broken layer of clouds, a couple of thousand feet thick. If precipitaion is caused by big cumulus clouds, similar to CB's, they will most often be reported as rain SHOWERS, not "rain".That is why a BKN020, thin layer of cumulus, and rain, is a non-real combination.I would think that these user selectable options is not that difficult to implement? I hope that all the complaints about cloud cover will be silenced in future upgrades.

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I got a better idea. How about advanced monitoring of Skew T/Log P charts. Where the TD/DP get close, put in a cloud layer. Unstable = cumulus and stable = stratus. Ok I want a cut of the profits for that idea TM.


Marc Lynn

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