Two centers, namely European Center for Medium-Range Weather Forecasts (ECMWF) and National Centers for Environmental Prediction (NCEP), used competitive ensemble forecasting methods since 1990s for long-term and long-range weather forecasting  and . Their ensemble forecasting methods NPPB widely used for wind speed/power forecasting. The ensemble forecasting methods comprise several numerical predictions integrated from different initial conditions. The initial conditions represent different initial uncertainties of the meteorological analysis. Both ECMWF and NCEP use perturbation theory for creating the initial conditions. ECMWF uses singular vectors to construct initial perturbations for maximum perturbation growth rate during the first two days  whereas for NCEP, breeding vectors are used to construct initial perturbations because breeding perturbation can compensate the accumulated growing errors ,  and . Detailed information on singular vector perturbation and breeding vector perturbation is reported in  and .