Interpretation
of the NWP system of equations
ÒWe use the model to forecast from
to
At
ÒThe analysis is obtained by adding to the background the innovation (difference between the observation and the
first guess) multiplied by the optimal Kalman gain matrixÓ
ÒThe optimal weight is the background error covariance
divided by the sum of the observation and the background error
covariance. 
ensures
that the magnitudes and units are correct. The larger the background error variance, the larger the correction to the first guess.Ó
ensures
that the magnitudes and units are correct. The larger the background error variance, the larger the correction to the first guess.ÓÓ