Regular and anomalous partial sums are computed for each model (see here). Each model's forecasts are verified using its own analysis as truth. All data are regridded using bilinear interpolation, if needed, to the G002 (2.5x2.5 degree) grid. A 40-year (1959-1998) climatology of the NCEP/NCAR reanalysis is used for computing anomalous partial sums.

Verification statistics are computed from the regular and anomalous partial sums. The equations used to calculate the verification statistics can be found here. Statistical signifance is calculated using a student-t test.

The wave breakdown for heights is done using Fourier Decomposition.

The NWP models evaluated are:
GFS00: U.S. NCEP Global Forecast System initialized at 00Z,
GFS06: U.S. NCEP Global Forecast System initialized at 06Z,
GFS12: U.S. NCEP Global Forecast System initialized at 12Z, and
GFS18: U.S. NCEP Global Forecast System initialized at 18Z.

The verification regions used are:
Global,
N. Hemisphere: 20N-80N,
S. Hemisphere: 20S-80S,
Tropics: 20S-20N,
PNA: 180E-320E, 20N-75N.