Model vs. forecast



  • Good morning

    Silly question perhaps - but I'm trying to understand how things work, and in particular, how Windy differs from other weather forecast providers (weather underground, google weather.com, national agencies such as meteo-france, etc, etc.).

    As far as I understand, the observation data is processed by various (a handful) of agencies, that then generate atmosphere models (ECMWF, GFS, NEMS, AROME, etc). These models are not consumer level products, but rather offer prediction on physical variables such as temperature, pressure, humidity and so on.

    This is then translated into user-friendly information ("light rain", "partly cloudy"....) by various proprietary software, that may base their predictions on one or more models, perhaps supplemented by additional observations (WU) or human expertise. This now results in effectively as may forecasts as weather data providers.

    Windy, as far as I understand, does not do the second part (interpretation, compilation, etc.) but merely displays (with a gorgeous interface !) the results of the models, and we can even choose which one. Although not quite : there is indeed a "forecast" layer in windy. Where is this derived from ? It this a straight model output, or is there further processing done by windy?

    To expand/generalize the question:
    Is my understanding, as outlined above, correct?
    Any further reading suggestions?
    Is there somewhere a comparison between the major operators (BBC, meteo France, WU.....) summarizing where their data comes from and what they do with it ?

    Thanks !


  • Sailor

    @jfmoyen said in Model vs. forecast:

    there is indeed a "forecast" layer in windy. Where is this derived from ? It this a straight model output, or is there further processing done by windy?

    To expand/generalize the question:
    Is my understanding, as outlined above, correct?
    Any further reading suggestions?
    Is there somewhere a comparison between the major operators (BBC, meteo France, WU.....) summarizing where their data comes from and what they do with it ?

    The « forecast » layer in Windy is the model forecast.
    Windy only visualises raw data of weather models and does not interpret them as official weather services can do. But for all weather app you find on internet be sure that the most part (almost 100%) of them do not involve human interpretation.
    The main difference with Windy is that most of them use GFS which is free, but with a low resolution when Windy uses the model of ECMWF which is known as the best for medium leadtime .
    If you want to learn more about Numerical Weather Prediction:
    https://en.m.wikipedia.org/wiki/Numerical_weather_prediction

    Obviously the official weather services use the output of the limited area models they have developed and the global models for longer leadtime. For instances Météo-France uses AROME, ARPEGE and IFS from ECMWF. Same DWD in Germany uses COSMO, ICON and IFS too. Same the UK MetOffice...

    I don’t think that WU is considered a major weather service, just a private one. In USA you should consider the NOAA/NCEP and the NWS which are major official weather services.
    http://www.ncep.noaa.gov



  • @idefix37 said in Model vs. forecast:

    But for all weather app you find on internet be sure that the most part (almost 100%) of them do not involve human interpretation.

    Thanks for the comment. I'm (mildly) surprised by this statement: if most of the weather apps just feed us the GFS data, how come they differ in what they show ? I have not run systematic tests, but played with 4-5 apps lately and I'm under the impression that they do not show the same forecast. Surely then the apps must do something more ? Interpolating perhaps, with different resolutions ?

    (does windy interpolate between grid nodes by the way, or do we just get the straight model output ?)

    Also, is there a way to find out what each app is doing, which model it is based on, etc. ? (short answer : probably not, unless they explain on their website and one takes the time to read it all, I presume ?)


  • Sailor

    @jfmoyen
    Why the weather apps using the same model do not show the same forecast?
    Probably because they don’t use the same way to display the data, they have different update time... (sorry I’m not a specialist and I have not carried tests about it)
    For instance Windguru and Windfinder explain that they use GFS as standard and WRF as option for a better resolution but this option is not free. You may check whether they display the same forecasts.
    Some apps have been developed by larger companies which employ meteorologists like Meteoblue who have made some adaption of the American NEMS model. They explain what they do, but the other ones don’t give so much details ... but all of them show a lot of advertising.
    https://www.meteoblue.com/en/weather/forecast/multimodel/tours_france_2972191



  • @idefix37 said in Model vs. forecast:

    They explain what they do, but the other ones don’t give so much details ... but all of them show a lot of advertising.

    As you say. And these are the two main reasons I'm using Windy (well, two of the three actually, the third being a great graphical display): (a) Windy tells me what it is doing and where the data comes from (being a scientist, I tend to be rather particular about knowing how the data is processed !) and (b) advertising is minimal in Windy (even Meteo-France is worth, shame on them....).


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