The Unprecedented 2023 North China Heatwaves and Their S2S Predictability

This study unravels the characteristics, mechanisms, and predictability of four consecutive record-breaking heatwaves hitting North China in June and July 2023. The first three heatwaves primarily influenced the northern part of North China and were accompanied by consistent anticyclonic anomalies in the upper troposphere. The anomalous anticyclone was caused by the British-Baikal corridor teleconnection along the polar front jet, particularly during the second heatwave. In contrast, the fourth heatwave was induced by a distinct low-pressure system, attributed to the Silk Road pattern along the subtropical jet. The presence of this low-pressure system and its interaction with atmospheric rivers and local topography led to the foehn wind, further contributing to the rise in surface temperatures. Sub-seasonal to seasonal models can effectively predict the occurrence of all heatwaves 2-5 days in advance despite underestimating the intensity. However, models exhibit limitations in providing reliable predictions when the lead time exceeds 2 weeks. Plain Language Summary In the summer of 2023, North China experienced four consecutive extreme high-temperature events, which are called heatwaves. This study investigates the main factors that cause the four events and shows how well the operational numerical models can predict the heatwaves. The first three heatwaves shared similar circulation, with high-pressure systems controlling North China. This local circulation anomaly was related to an upstream quasi-stationary wave train along the polar front jet. The fourth heatwave was associated with a low-pressure system over North China and an upstream quasi-stationary wave train along the subtropical jet. Moreover, predictions from operational models demonstrate their capability to forecast the occurrence of high temperatures 2-5 days ahead, with an underestimation in the intensity. However, models are not reliable when it comes to predicting heatwaves 2 weeks in advance.