A method of extended range forecasting, the low-frequency synoptic map (LFSM), is introduced in this paper. Unlike statistical forecasting, numerical prediction, and synoptic forecasting, the LFSM is a new approach that can be used for extended range weather process forecasts. The key technical points of the LFSM are the low-frequency system (low-frequency cyclone and low-frequency anticyclone) and the corresponding low-frequency airflow. Its synoptic significance is that the LFSM can reflect the formation, dissipation, maintenance, and motion of synoptic systems that cause weather processes, as well as the evolution of atmospheric circulation. Its advantage lies in its characteristics, including temporal periodicity and persistence, spatial continuity and similarity, and the quasi-steady properties in an area, so the LFSM can easily predict weather processes and has a longer forecast validity period. Operational practice using the LFSM in the Shanghai Climate Center from 2008 to 2012 indicates that it can predict strong precipitation processes 15-45 days in advance.