Questions about data accuracy



  • First let me say (again) that I really like the Windy user interface and the types of data it provides. However, I'm trying to reconcile some of the weather data with what I see on other sites.

    The other site I have used for a long time is weather.us. I also provides access to the ECMWF forecast with a modest subscription fee. The problem with weather.us is that it has a very klunky user interface. I would love to switch over to Windy as my go-to source of weather.

    However, I've noticed that the ECMWF predictions between the two sites can be significantly different and it is not clear why that would be.

    1. I have made sure that both are using the same run of the ECMWF model
    2. I have made sure the locations are the same (to within a couple hundred meters)

    Despite that I will sometimes get temperature predictions for the same hour that vary by 5ºF. As an amateur astronomer, I'm very interested in cloud predictions. I find significant differences between those as well

    As an example, I was looking at the weather in a nearby city I'm going to tonight

    At 9 PM here are what the two sites say:

    (Temp, high clouds, middle clouds, low clouds)

    Windy:       51º, 09%, 06%, 0%
    Weather.us:  56º, 21%, 01%, 0%
    

    At 12 PM we have:

    Windy:      47º, 24%, 34%, 0%
    Weather.us: 53º, 28%, 28%, 0%
    

    These are just two examples, but the discrepancies are rampant. They are not huge, but they are worrisome.

    I have asked weather.us if they have any ideas why these significant discrepancies would exist. Of course, they didn't really know but did say they apply an elevation correction to some of the data. I wouldn't think that would be done for cloud predictions. It also seems unlikely that an elevation correction would yield a 5ºF temperature difference.

    So I'm asking the Windy team if they have any thoughts on this. Unfortunately, I don't know of a third site I could check to see who they agree with.

    To be honest, I probably trust weather.us more. It is run by a team of meteorologists and you would think they would know what they are doing. As far as I can tell the Windy site is run by weather enthusiasts.

    I would appreciate any ideas about why this difference might exist.


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