The 2019 New Year Stratospheric Sudden Warming and Its Real‐Time Predictions in Multiple S2S Models

Abstract Using multiple data sources, favorable conditions for the 2019 SSW event and its predictive skill from 11 subseasonal to seasonal (S2S) forecast models are explored in this study. This mixed‐type (displacement to split) SSW event occurred under moderate El Niño, easterly quasi‐biennial oscillation (QBO) together with solar minimum, and phases 4–6 of the Madden‐Julian oscillation (MJO). A strong positive PNA formed and developed in the troposphere before this SSW event, which is associated with enhanced and wave‐1‐dominated eddy heat flux. The predictive limit to this SSW onset is beyond 18 days in most S2S models, longer than the average predictive limit in existing literature. This high predictive skill may originate from the favorable initial conditions (QBO, MJO) and boundary…