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The following scores are to be calculated for all parameters against both analysis (except mean sea-level pressure) and observation:

Wind

Mandatory:

• rms vector wind error
• mean error of wind speed

Other parameters

Mandatory

• Mean error
• Root mean square (rms) error
• Correlation coefficient between forecast and analysis anomalies (not required for obs)
• S1 score (only for MSLP and only against analysis)

Additional recommended

• mean absolute error
• rms forecast and analysis anomalies (not required for observations)
• standard deviation of forecast and analysis fields (not required for observations)

Definition

The following definitions should be used
Mean error 

...

Root mean square (rms) error

rmsrmse = \sqrt {\frac{1}{S_w} \sum_{i=1}^n w_i (x_f - x_v)_i^2 }

...

rms vector wind error

rmsrmse = \sqrt {\frac{1}{S_w} \sum_{i=1}^n w_i (\vec{V}_f - \vec{V}_v)_i^2 }

...

= the forecast value of the parameter in question;

x_v

= the corresponding verifying value;

x_c

= the climatological value of the parameter; n = the number of grid points or observations in the verification area;

M_{f,c}

= the mean value over the verification area of the forecast anomalies from climate;

M_{v,c}

= the mean value over the verification area of the analysed anomalies from climate;

\vec{V}_f

= the forecast wind vector;

\vec{V}_v

= the corresponding verifying value;

The differentiation is approximated by differences computed on the verification grid:

...

• Verification against analyses:

  Mathinline
  w_i = \cos \theta_i

  , cosine of laltitude athe latitude at the the grid point i

• Verification against observations:

  Mathinline
  w_i = 1/n

  , all observations have equal weight