A study identifies the Quasi-Biennial Oscillation (QBO) as a key predictor of the southern drought–northern flood (SDNF) pattern in East Asian summer precipitation. The QBO, a tropical stratospheric wind pattern, modulates precipitation in East Asia, explaining up to 75.8% of the variability in summer rainfall. A statistical model incorporating the QBO can predict summer floods and droughts at least three months in advance, with over 30% of the SDNF pattern attributed to the QBO in 2020 and 2021. The study highlights the importance of the QBO in seasonal forecasts for East Asian summer precipitation, suggesting its potential for improving disaster preparedness. The QBO influences precipitation through subtropical circulation and wave feedback mechanisms, with its effects extending from the stratosphere to the surface. The study also emphasizes the need to incorporate the QBO into seasonal forecasting models, as it plays a significant role in the leading mode of East Asian summer precipitation. The findings suggest that understanding the QBO could enhance the accuracy of seasonal forecasts for extreme weather events in East Asia.A study identifies the Quasi-Biennial Oscillation (QBO) as a key predictor of the southern drought–northern flood (SDNF) pattern in East Asian summer precipitation. The QBO, a tropical stratospheric wind pattern, modulates precipitation in East Asia, explaining up to 75.8% of the variability in summer rainfall. A statistical model incorporating the QBO can predict summer floods and droughts at least three months in advance, with over 30% of the SDNF pattern attributed to the QBO in 2020 and 2021. The study highlights the importance of the QBO in seasonal forecasts for East Asian summer precipitation, suggesting its potential for improving disaster preparedness. The QBO influences precipitation through subtropical circulation and wave feedback mechanisms, with its effects extending from the stratosphere to the surface. The study also emphasizes the need to incorporate the QBO into seasonal forecasting models, as it plays a significant role in the leading mode of East Asian summer precipitation. The findings suggest that understanding the QBO could enhance the accuracy of seasonal forecasts for extreme weather events in East Asia.