I would like to know how the resolution of a Numerical Weather Prediction model conceptually works.


"Global Forecast System's forecasts with 0.5° horizontal spatial resolution"

"NCEP’s reforecast is based on the Global Ensemble Forecast System (GEFS), which has horizontal grid increments of approximately 1°."

Are these two sentences talking about the same thing? In this case, GFS has more resolution, doesn't it?

  • $\begingroup$ yes GFS has higher resolution $\endgroup$
    – user1066
    Commented Feb 6, 2021 at 8:31

1 Answer 1


Yes, the deterministic GFS model (one model) has higher spatial resolution than the GEFS models (31 models). That is, that the latitude and longitude of the entire world is incremented by 0.25° in the GFS and 0.5° in the GEFS (they upgraded both in the past two years). When people say "high resolution," think of it like "more pixels" on a video (like 1080p).

On a more technical note, the GFS's (internal) resolution was once described as T-numbers, which counts the number of waves that can be fitted. The GFS could fit 1534 waves. However, since the upgrade in the dynamical core, the resolution has taken a different number. I don't exactly know the physical interpretation of the C-number, but the GEFS's C-number is currently C384 (my guess is that it is the number of cubes on one face of the cubed sphere).


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