• Administrator

     photo: josep-castells; licence: cc

    How the weather forecast works

    There is thousands of weather stations around the world. Valuable data from these stations and also from planes, ships, buoys and satellites are gathered together, so we have idea how the earth’s atmosphere looks like at a certain time. Of course, all the data must be observed at the same time and this time is called “reference time”.

    All these data are then put into computer. Rather supercomputer, with huge computation power, usually owned by states or meteorology agencies.

    After few hours of computation the computer outputs the result, that is called “forecast model”. The process of computing this model is called “running the model”.

    Forecast model is bunch of huge computer files in weird formats, containing just numbers, and numbers and again numbers.

    Meteorologists and companies all over the world download these files on regular basis, and based on these data, create those beautiful icons that you are familiar with or Windy.com animations and visualisation you like so much.

    Some “forecast models” can be downloaded for free, some must be paid for.

    Some forecast models cover whole world. These are called “global models”. “Local models,” on the other side cover just smaller area.

    There are two major global forecast models: GFS and ECMWF, called also Euro.

    Most of the weather sites use only GFS model because its free, while ECMWF must be paid. On Windy.com we use both and you can choose which one you want to use. We have decided to pay for ECMWF because we consider it much more advanced and precise than a GFS. Studies show, that ECMWF is most accurate forecasting model in the world.

    How the forecast model looks like

    Forecast model is bunch of big computer files in weird data formats. We download these files from meteorology agencies on regular basis, whenever new version of files are available. Each download is called “update”. For example GFS model is updated each 6 hours, while ECMWF is updated each 12 hours. See the exact times on following link.

    Forecast model contains numbers, that describe how the earth’s atmosphere will look in next days in each three hours intervals. Some local models forecast weather even in hourly intervals.

    But computing forecast for each place in the world would be computationally very difficult. Therefore model is computed just for some places in the world. These places are called “grid” and density of such a grid is called “resolution”.

    And what happen if you want weather forecast just between these points in a grid? We just look at the closest points in the grid and make some average out of it. This process is called “interpolation”.

    If you click on a map on Windyty and move picker around the map, the numbers you see are interpolated numbers for any place in the world.

    On Windy we use models GSF with 22km resolution grid, ECMWF with 9km resolution grid and a lot of local models with resolution even 3km.

    (Special thanks to @ajf_hodgson for the grammar check)

    Shortened version of this link: on.windy.com/ForecastModel

  • be nice to have more models added, do you plan to add more models?

  • I can´t see or choose between GFS or ECMWF at Android app...is this already implemented?

    • [list item](link url)

  • "and a lot of local models with resolution even 3km..."

    So which local models do you use then? And if you use local models (on a certain zoom stage, I guess) how can the user know which one is used for this certain grid point? It would be useful to know that.



  • Hi Ivo, thanks for the great explanation! Can you please explain how the "NEMS" model and the "Waves and Sea" model are derived? Thank you.

  • I love this


  • Hi Ivo,

    Just wanted to thank you! I just started flying sailplanes and windytv is just the best free weather site I've found so far! Very good data and amazing presentation! Cloud base and visibility is super useful in particular but I also love just looking at the weather systems globally.


  • | Premium

    Hi, I have noticed when you bring up the compared models metrogram, it's hard to see the little icons for the clouds, snow etc. Is this something that can be revised at some point so it's easier to see?


    • ![list item]([image url](link url))
  • Administrator

    @jmatthys Send screenshot

  • Kiter | Premium

    I really appreciate that I can compare the forecast for different models for my site. Would be helpful if I could see at what time the different models where run/updated.

  • Kiter | Premium


    No need to answer. I have found where the updated times can be found.

  • @ivo Hi! I am in China,and I also a kite surfer. This APP and web is the best weather forecast software and website I ever seen. It's much better than windguru which I offen used before. I expect to allow user to add own favourate spot and share with others.

  • 78/5000
    That means swell 1 2 and 3 please how can one interpret this data

    thank you

  • | Premium

    Hi! Nice work! Congratulations!
    Do you plan future time steps of one hour?

  • Hi all,

    I would like to ask where do you get the raw data (I mean the data saved grid or other format). Can I directly download the data with free of cost?


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