Abstract:In the light of the chaotic characteristics inherent in the atmosphere, a strategy about 10—30 d forecasting is developed. Actually, the atmospheric predictability depends on the spatial and temporal scales. Although the 10—30 d forecasting has exceeded the limit of predictability of daily weather, some predictable components, like some planetary-scale motions which could be forecasted very well in 10—30 d forecasting, could also be found. Based on the numerical models, a method to obtain the predictable components in 10—30 d forecasting is illustrated in this study. Furthermore, the theory promoted methods and strategies for obtaining the predictable components and chaotic components. Our conceiving of 10—30 d forecasting can directly employ the current variational data assimilation system and numerical model, which make sure its feasibility.