Hi Ben,Often, perhaps, but just as often I have seen no TS yet CB and yes thunderstorms. Many users reported recently over Europe CB in their reports with plenty of thunderstorms.. yet TS not reported.All documentation I have (real world experiences asside, I need to go on hard reproducable documentation to prove to the non-believing public!) says that CB indicates cumulonimbus.. Not "Cumulus buildup" or "convective cumulus" as even I was tought in the past. Cumulonimbus indicates thunderstorm by definition. I agree that there is a difference, but we are limited with out representation technology here.In FS2002 there is either stratus, cumulus or cumulonimbus clouds to choose from.I welcome comments and suggestions on this topic, I am sure there is a better way to handle it for better realism (there always is) but I need some documentation to support logic changes. Personally I would like to see cumulus stage thunderstorms (or "cumulus buildup" when CB encountered, and mature or dissipating stage thunderstorms when TS encountered (more along the lines of what I see in real life). Actually this type of more intelligent cloud selection (based on new intelligent cloud sets) is being worked on.-Damian[table border=0" cellspacing="30" cellpadding="0][tr][td align = "left"]Damian ClarkHiFi Simulation SoftwareDeveloper of ActiveSkyThe next-generation weather environment simulation for FS2002!http://hifi.avsim.net/activesky[/td][td]http://hifi.avsim.net/activesky/images/wxrebeta.jpg][/td][/tr][/table://http://hifi.avsim.net/activesky/ima...][/tr][/table

Hi Damian,I have taken a look into my weather book from my training and searched for information about CBs. Unfortunately the text is not very clear. While it doesn't say that the existence of CBs *automatically* leeds to thunderstorms (i.e. thunder, lightning, heavy percipitation) it also says that thunderstorms are "very likely and can be expected". Not very helpful, eh? :-doh However, an existing thunderstorm always implies that there is a CB cloud or a CB cloud has turned into this thunderstorm, depending on how you put it.Maybe the reason for the fact that some people (including myself) have experienced forcasted CBs which haven't turned into TS in real life and are a little bit surprised that Flight Simulator always plays thunderstorm sounds when there is a CB in the METAR is the fact that real life forcasts are never (and never *can be*) 100% correct. Also we shouldn't forget that weather is a VERY dynamic process and constantly in motion. Large, continent-sized weather systems play a role in the development just as an asphalt parking lot that quickly heats up in the sun. And, after all, MSFS is a flight simulator not a weather simulator and my weather has never looked better and more realistic since I use ActiveSky wxRE. :-beerchug

Damain,I think people are confusing thunderstorms and cumulonimbus because one is associated with the other. This leads to an assumption that if you have one, then you have the second. This of course is false.You stated, Cumulonimbus indicates thunderstorm by definition. Actually it is the other way around. Thunderstorm indicates Cumulonimbus by definition.You wanted documented evidence to pass along. Well, my college textbooks on meteorology are not as useful as internet links, so here you go:http://www.mountwashington.org/glossary/glosa.htmlThe selected words and definitions taken from:Encyclopedia of Climate and WeatherStephen H. Schneider, Editor: Oxford University Press, Oxford 1996cumulus (Cu) - Widely known as "fair weather clouds," cumulus clouds are one of the three major cloud types that comprise the ten main groups or genera. Cumulus (a heap, pile, or mound) or convective clouds are defined as many individual clouds detached and separated by clear skies. The clouds are dense, developing vertically into domes or towers that resemble cauliflower. The sunlit upper portion is brilliant white, and the bases are dark and gray. The outlines of the clouds are sharp when they consist of water droplets and fuzzier or diffuse when they consist of ice crystals. Besides the genera cumulus clouds, there are four other genera that are hybrids of cumulus clouds and differ from the most generic kind of cumulus cloud: cirrocumulus, altocumulus, stratocumulus, and cumulonimbus. In addition to the more general cumulus formation, when cumulus clouds have only slight vertical ascent and are usually confined to the lowest 2 kilometers of the atmosphere they are referred to as cumulus humilis; when cumulus clouds reach moderate vertical extent (generally between 2 to 6 kilometers above the ground) and exhibit small protuberances they are termed cumulus mediocris; finally, when cumulus clouds extend high up into the atmosphere (generally 6 kilometers or more above the ground) and their bulging parts resemble cauliflower they are called cumulus congestus. [see also cirrocumulus; altocumulus; stratocumulus; and cumulonimbus.]cumulonimbus (Cb) - A cumulus cloud of significant vertical extent which is producing heavy precipitation. The cloud often has an anvil-shaped appearance on top, and it is bubbly (cauliflower) shaped on the sides. The top of the cloud is sufficiently dense to filter out sunlight so that the cloud base looks dark. Cumulonimbus clouds are one of four genera that are hybrids of cumulus clouds.thunderstorm - A storm involving one or more cumulonimbus clouds which are accompanied by lightning and thunder. The amount of rain, precipitation, hail, lightning, and outflow wind speed can vary according to the microphysical characteristics (cloud condensation nuclei), the thermodynamic instability, and wind shear characteristics of the environment.As you can see, the definition tries to cover itself for those instances where lightning is observed, but not precipitation.A second source comes from the NWS in their Federal Meteorological Handbook No. 1, Appendix Ahttp://205.156.54.206/oso/oso1/oso12/fmh1/...pa.htm#appalinkcumulonimbus. An exceptionally dense and vertically developed cloud, occurring either isolated or as a line or wall of clouds with separated upper portions. These clouds appear as mountains or huge towers, at least a part of the upper portions of which are usually smooth, fibrous, or striated, and almost flattened.thunderstorm. A cumulonimbus cloud that is accompanied by lightning and thunder, or for automated systems, a storm detected by lightning detection systems.In both references, the definition ties TS to CB and not the other way around.As for the definition of how the METAR should be interpreted, this message thread focuses on whether CB is used when there is a thunderstorm.Here is the answer for METAR issued in the United States from the Federal Meteorologicial Handbook No. 1, Chapter 12 - Codinghttp://205.156.54.206/oso/oso1/oso12/fmh1/...12.htm#ch12linkSection 12.6.8.b(4) Present Weather Group Descriptor Qualifier"The descriptor thunderstorm (TS) may be coded by itself, i.e., a thunderstorm without associated precipitation, or it may be coded with the precipitation types of rain (RA), snow (SN), ice pellets (PE), small hail and/or snow pellets (GS), or hail (GR). For example, a thunderstorm with snow and small hail and/or snow pellets would be coded as "TSSNGS". TS shall not be coded with SH."Then further in Section 12.6.9 Sky Condition Group, at the end of the section, it states:"At manual stations, cumulonimbus (CB) or towering cumulus (TCU) shall be appended to the associated layer. For example, a scattered layer of towering cumulus at 1,500 feet would be coded "SCT015TCU" and would be followed by a space if there were additional higher layers to code."From these very clear definitions and METAR coding instructions in the United States, one should never hear thunder and/or see lightning when the METAR is coded with a CB in the sky condition group unless there is a TS symbol in the present weather group. Notice that the CB qualifier is only coded at manual stations, not automated stations.Additionally, the remarks section of the METAR may provide information about thunderstorms, lightning, or CB in the vicinity or at a distance from the station. However, I don't believe ActiveSky takes the remarks into consideration when generating weather.You stated, Often, perhaps, but just as often I have seen no TS yet CB and yes thunderstorms. Many users reported recently over Europe CB in their reports with plenty of thunderstorms.. yet TS not reported.There are many possibilities for this. The first is that the user may hear thunder and only CB is reported, yet it is possible that the remarks section of the report mentioned the lightning or thunder. The thunder could have been in the distance. Secondly, each country of the WMO may deviate slightly from the standard coding practices, though it is not likely. More likely is an observer manually filing the report and confusing TS with CB as discussed above.The important factor overall is that cumulonimbus only describes extensive vertical development of cumulus clouds that are producing rain. If no rain is generated, then there are other classifications assigned to the cumulus cloud, for example TCU. There is no indication and should be no assumption that thunder and lightning are automatically present when a CB is reported.Since ActiveSky does not consider the remarks section of the report, you could allow thunderstorms anytime CB is reported just to cover the possibility, but then you will have users saying I have thunderstorms in my simulator and I don't hear any thunder outside. It's a catch-22 situation.Personally, I think you should follow the METAR standards until the remarks section can be interpreted by the ActiveSky program.Bruce

HiGood post Bruce. I was trying to collect some references on the subject myself but now I don't have to do that. You have covered it all, I think. I realize that there are some limitations in the way clouds are visualized in FS2002 so it isn't an easy task to put something together that covers all possibilities. One way to represent CB without thunderstorms might be to put in very thick cumulus 6 or 7 octas. One thing I noticed yesterday with wxRE is the thickness of the thunderstorm clouds. The report said FEW012CB BKN040 and that resulted in lightning from clouds that were only 1-2000 ft thick. Not very realistic. Is it possible to put in "Minimun thunderstorm thickness" as well, as an option? /olle

Hi Bruce,Thanks very much for the detailed information here! It sure helps..Currently CB triggers the "Cumulonimbus" engine within FS2002, which in turn triggers lightning. I think eventually the best way to handle this is to only definitely create "FS CB/Tstorms" when TS reported, and then to conditionally/randomly generate them when CB reported (conditional factors: temp, pressure). If no TS generation, then simulate unstable cumulus (via thick(towering) dense cumulus). The remarks section is something I don't forsee being able to process - it is so different everywhere you go.. there'd probably be 100 different processing routines for 100 different countries.Anyhow, I will work on this additional logic... Thanks again for your help!-Damian[table border=0" cellspacing="30" cellpadding="0][tr][td align = "left"]Damian ClarkHiFi Simulation SoftwareDeveloper of ActiveSkyThe next-generation weather environment simulation for FS2002!http://hifi.avsim.net/activesky[/td][td]http://hifi.avsim.net/activesky/images/wxrebeta.jpg][/td][/tr][/table://http://hifi.avsim.net/activesky/ima...][/tr][/table