Despite global warming, persistent wet–cold compound extreme events (PWCEs) during wintertime still occur frequently in China, causing significant disruption of human and social activities. However, their full range, precursors, and evolution characteristics remain unclear. In this study, 252 PWCEs in China during cold seasons from 1961 to 2023 are objectively identified and further classified into the South China (SC), Western China (WC), and Central China (CC) types. Although the frequency of PWCEs has decreased under global warming, they still exhibit high extremity, and the WC-type events even show an upward trend in intensity. The three types of PWCE events share a similar “north high–south low” meridional pattern over mid–high latitudes but demonstrate significantly different circulation evolution attributes and precursors: the SC type is dominantly driven by cold-air outbreak linked to the Baikal blocking–East Asian trough; the WC type is controlled by the zonal wave train along the South Asian subtropi-cal westerly jet; the CC type is embedded within a well-organized midlatitude great-circle wave train across Eurasia. Their associated moisture transports also show diverse pathways: the SC type primarily harvests moisture from the South China Sea, the WC type from the India–Burma trough, and the CC type from both the western North Pacific anticyclone and the South China Sea. The precursors for PWCEs originate mainly from the Madden–Julian Oscillation modulating the tropical circulation and moisture transports, especially for the WC and CC types. These findings highlight the diverse formation links and precursors underlying PWCEs in China, offering insights for improving subseasonal prediction of the compound extreme events in China.

Based on a combination of six Chinese climate models and three international operational models, the China multi-model ensemble (CMME) prediction system has been upgraded into its version 2 (CMMEv2.0) at the National Climate Centre (NCC) of the China Meteorological Administration (CMA) by including new model members and expanding prediction products. A comprehensive assessment of the performance of the upgraded CMME during its hindcast (1993–2016) and real-time prediction (2021–present) periods is conducted in this study. The results demonstrate that CMMEv2.0 outperforms all the individual models by capturing more realistic equatorial sea surface temperature (SST) variability. It exhibits better prediction skills for precipitation and 2-m temperature anomalies, and the improvements in prediction skill of CMMEv2.0 are significant over East Asia. The superiority of CMMEv2.0 can be attributed to its better projection of El Niño–Southern Oscillation (ENSO; with the temporal correlation coefficient score for Niño3.4 index reaching 0.87 at 6-month lead) and ENSO-related teleconnections. As for the real-time prediction in recent three years, CMMEv2.0 has also yielded relatively stable skills; it successfully predicted the primary rainbelt over northern China in summers of 2021–2023 and the warm conditions in winters of 2022/2023. Beyond that, ensemble sampling experiments indicate that the CMMEv2.0 skills become saturated after the ensemble model number increased to 5–6, indicating that selection of only an optimal subgroup of ensemble models could benefit the prediction performance, especially over the extratropics, yet the underlying reasons await future investigation.

As an important atmospheric circulation system in the mid–high latitudes of East Asia, the Northeast China cold vortex (NCCV) substantially influences weather and climate in this region. So far, systematic assessment on the performance of numerical prediction of the NCCVs has not been carried out. Based on the Beijing Climate Centre (BCC) and the ECMWF model hindcast and forecast data that participated in the Sub-seasonal to Seasonal (S2S) Prediction Project, this study systematically examines the performance of both models in simulating and forecasting the NCCVs at the sub-seasonal timescale. The results demonstrate that the two models can effectively capture the seasonal variations in the intensity, active days, and spatial distribution of NCCVs; however, the duration of NCCVs is shorter and the intensity is weaker in the models than in the observations. Diagnostic analysis shows that the differences in the intensity and location of the East Asian subtropical westerly jet and the wave train pattern from North Atlantic to East Asia may be responsible for the deficient simulation of NCCV events in the S2S models. Nonetheless, in the deterministic forecasts, BCC and ECMWF provide skillful prediction on the anomalous numbers of NCCV days and intensity at a lead time of 4–5 (5–6) pentads, and the skill limit of the ensemble mean is 1–2 pentads longer than that of individual members. In the probabilistic forecasts of daily NCCV activities, BCC and ECMWF exhibit a forecasting skill of approximately 7 and 11 days, respectively; both models show seasonal dependency in the simulation performance and forecast skills of NCCV events, with better performance in winter than in summer. The results from this study provide helpful references for further improvement of the S2S prediction of NCCVs.