Rain forecasts issue


  • Meteorologist

    I believe that there is an issue here with the rain forecast. Data showed by 3h are different than the forecast by 1h.

    Look here :
    F3F4C8DD-90EF-4CD1-8D30-A824869395D6.jpeg
    Total rain forecast for Saturday (today) foreseen by IFS (3h fcst) is 0.5 + 0.2=0.7mm

    Now, look here when I check the forecast by 1h :
    2C5962A2-4473-43AB-88EC-515F10E88597.jpeg
    Here for the same period, Saturday afternoon, total is different and is 0.3mm only

    Where the difference comes from ?


  • Sailor Moderator

    @Yves70
    Your remark is similar to this one:
    https://community.windy.com/topic/12235/hourly-forecast-with-differences-to-standard-forecast?_=1594533107049
    In Meteogram Windy displays only rain amounts equal to 0.1 mm or more.
    So the 0.2 mm at 17h i.e. during the last 3 hours, could be the result of less than 0.1mm per hour, let’s say 0.08+0.09+0.06=0.23~0.2
    It is more difficult to explain the 0.5 mm at 14h as in addition to 0.3mm at 13h it would need 0.1+0.1 during the other 2 hours. May be due to the way how are these values are rounded ??


  • Meteorologist

    @idefix37
    Thanks for your comment !

    We are talking about small quantities of rain, of course. In general below 0.4mm you even don’t really notice it if you are outside ! It could be related to the the way it is rounded but as you highlight, the 0.5mm is harder to explain.

    I wanted to mention it again to be sure it is not related to something else, sometimes small inconsistencies like in the case here hide in fact a bigger problem. Windy team should just comment and confirm.

    I can monitor it during the coming days/weeks, especially a day with much more rain to see if the difference 3h/1h rain forecast remains still small or not


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