Subseasonal predictability of the extreme autumn rainfall event in West China in 2021

In 2021, an exceptionally intense autumn rainfall event occurred in West China (WC), breaking historical precipitation records since 1961. A notable northward migration of rainfall center was observed during the season. This study utilized real-time forecast data from the ECMWF (European Centre for Medium-Range Weather Forecasts) and CMA (China Meteorological Administration) models under the S2S (Subseasonal-to-Seasonal Prediction) project to examine the subseasonal predictability of the extreme ARWC event and its associated systems, providing a theoretical basis for forecasting extreme autumn rainfall. The results showed that both models underestimated the observed anomalous precipitation, however, ECMWF was able to predict the spatial distribution and intensity of different phases of the event up to 8 days in advance, while the CMA model exhibited poor skill. ECMWF and CMA both successfully predicted the intraseasonal northward migration of the rainfall 8 days and 5 days in advance, respectively. Further analysis revealed that ECMWF and CMA can reproduce the mid-high-latitude wave patterns associated with the intraseasonal variations in the EAWJ at lead times of 1-10 days, contributing to better predictions of the intraseasonal northward migration of the rainfall. Their ability to predict the tropical convection differed, with ECMWF more accurately reproducing the anomalous dipole tropical convection activities over the Indo-Pacific Warm Pool and the central-eastern Pacific 1-22 days in advance, and the characteristic that the convection eventually weakens over the maritime continent. This led to better predictions of the intraseasonal variations of the WPSH, giving the ECMWF model a higher forecasting skill for both periods of the extreme ARWC in 2021 compared to the CMA model.