To Identify the Forecast Skill Windows of MJO Based on the S2S Database

As a practical reflection of the opportunity window of Madden‐Julian Oscillation (MJO), there are intermittent periods of relatively high forecasting skills, namely the forecast skill windows. Robust forecast skill windows are identified based on the subseasonal‐seasonal reforecast database, during which the majority of models show high forecast skills. A total of 15 MJO forecast skill windows during 1993–2020 have been identified. Most of the forecast skill windows are closely associated with active MJO events with high amplitude. Whether a high‐skill forecast window appears significantly depends on the magnitude of MJO intensity during the same period. The maintenance of active strong MJO events is potentially related with the warmer surface sea temperature anomalies in the western Pacific. Further research into such processes may unveil the MJO development mechanism and improve the MJO forecast skill. Plain Language Summary With the continuous development of the economy and society, there is an increasing demand for subseasonal‐seasonal forecasts. The forecast skills of Madden‐Julian Oscillation (MJO) show significant high and low variabilities, associated with specific conditions. MJO forecast skill windows are confirmed based on subseasonal‐seasonal (S2S) forecast products in this study. These windows represent the periods when most models in the S2S database can accurately capture the MJO signal, indicating the MJO forecast skill experiences intermittent enhancements. When the MJO intensity is high in the same period, the high‐skill forecast window is more likely to appear. One potential reason for the maintenance of strong MJO is the anomalously warmer sea surface temperature in the western Pacific, along with other potential factors, providing the opportunity to forecast MJO with high skill. When the opportunity arises, the forecast skill of MJO improves, highlighting the significance of exploring the processes leading to the occurrence of these skill windows. This provides a pathway for more accurate MJO forecasting and improves the predictability of S2S. Key Points Robust forecast skill windows of Madden‐Julian Oscillation (MJO) are identified based on the subseasonal‐seasonal reforecast database The forecast skill windows are mostly related to strong MJO amplitude Warmer sea surface temperature anomalies in the western Pacific potentially favors the maintenance of active strong MJO events