It's often said that the ECMWF model is more accurate than the GFS. But what are the reasons why? Also, how does the NAM compare with these two and other forecasting models?
- Spatial (horizontal and vertical) and temporal resolution
- Dynamical core
- Handling of some complex non-linear physical processes (i.e. snow)
- Topography representation
- How the mathematical equations are numerically implemented
- The computer used
These are some of the main differences between 2 given numerical weather model.
With that being said, the same model will give different results when run on a different computer (Hong et al. 2013).
Hong S-Y, Koo M-S, Jang J, et al. (2013) An Evaluation of the Software System Dependency of a Global Atmospheric Model. Mon Weather Rev 141:4165–4172. doi: 10.1175/MWR-D-12-00352.1
A difference of accuracy between weather models can be due to different factors, one of these is certainly the availability of "good" initialization data. As pointed out in Bradley Ballish (NOAA/NCEP) in his AMS presentation the accuracy of GFS has improved drastically when ECMWf initaliziation data have been used. Furthermore, I think there is a big difference in computational power between the two centers, ECMWF center has bigger and faster supercomputers.