?Abstract From 1 to 18 October 2025, a rare persistent overcast and rainy event with insufficient sunshine occurred in Shandong Province during the autumn harvest and sowing period, featuring long duration, distinct stages, large accumulated rainfall, and the combination of continuous rain and local torrential rain. Using surface meteorological observations, NCEP reanalysis data, ERA5 reanalysis data, and the HYSPLIT Lagrangian integrated trajectory model, this study analyzes the causes of the event. The results show that: (1) During this event, the Western Pacific Subtropical High (WPSH) was significantly stronger than the climatological normal, with its ridge line 4.5 latitudes northward and westward-extending ridge point 10.2 longitudes westward of the multi-year average. Meanwhile, the Siberian High underwent two successive intensification processes during the event. The anomalously strong WPSH and intensifying Siberian High jointly formed the climatic background for this continuous rain. (2)Throughout the event, the Eurasian continent maintained a typical "two troughs-one ridge" circulation pattern. Significant positive anomalies of southwest airflow and air temperature were observed at 700 hPa and 850 hPa. The 200 hPa upper-level westerly jet was much stronger than the normal and shifted 5–10 latitudes northward. Such large-scale circulation configuration favors the persistent maintenance and staged development of the continuous rain event. (3)Ranked by water vapor contribution rate, the main water vapor sources are sequentially the East China Sea, Bay of Bengal, South China Sea and Atlantic Ocean, which is closely related to marine tropical cyclone activities. (4)During the heavy rainfall period, the lower troposphere featured MPV2 < 0 with weak conditional symmetric instability, providing unstable stratification conditions for rainfall intensification.