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Gfs Accuracy


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  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks


    I am putting this in here as it means anyone can refer to this whenever they wish to see how GFS is doing in terms of accuracy using as accurate and comprehensive a check as any amateur can run.

    From time to time I will update this and try and compare recent checks with older ones to see if any changes have occurred in accuracy.


    Just as an addition to the GFS checks, I have just done a fairly quick check on the approximately 45 full runs that I have run checks on from late October 2004 up to this week.

    The statistics are these

    39 out of 45 were rated good from T+120, and around 30 were rated as quite good to good from T+144. Even at T+168 some 28 were rated good.

    Now to have those sort of statistics to my mind, the ability to say 7 days ahead, in something like 62% at 7 days would give a largely correct forecast for the air mass, wind direction, weather, max and min temp and rainfall along with pressure being within about 5mb of the actual, is quite something to an old ex forecaster.

    At T+120 hours, 5 days, for all this to be in place with a % of 87% is even more astonishing.

    Keep the faith with GFS, and the other computer models which go out to about 5-6 days. But do stick to the same time each day for each computer.

    Maybe some of the faults in the forecast are those of not noting what was actually said, rather than the forecast being wrong. It could of course be that the interpretation of the data from the computer was wrongly assessed. I do know from personal experience of 4-5 years at a weather centre that trying to get the main thrust of the forecast to everyone is, for some reason, quite difficult.

    John Holmes

    Senior Forecaster for Net Weather

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