Abstract:From 23 to 29 July 2025, extreme torrential rain occurred in Beijing. Based on multi-source observation data, ERA5 reanalysis data, RISE and RMAPS-NOW high-resolution grid analysis data, this paper analyzes the characteristics of rainfall stages, the spatio-temporal features and causes of this event. The results show that the July 2025 extreme torrential rain occurred under a stable circulation background where the subtropical high was significantly westward and northward and stronger than usual, with active tropical systems on its southern side. The lower atmosphere had warm anomalies, with a positive water vapor flux anomaly at 925 hPa and a significantly enhanced water vapor convergence zone in northern and eastern Beijing, creating conditions of high temperature, high humidity and high CAPE. This rainfall event was featured with long duration, much more accumulated precipitation, nocturnal occurrence, localization and extremity. According to the daily evolution of precipitation, the whole event is divided into four stages, corresponding to the swing of the 588 dagpm contour position of the subtropical high. Extreme torrential rain occurred in Stage 2 and Stage 3, concentrated in the northern mountainous areas of Beijing, featuring a “weak overall but strong locally” pattern, and also accompanied by extreme short-time heavy rainfall. The focus analysis on this two stages indicates that, the radar echoes in Stage 2 showed obvious backward triggering and “train effect” characteristics, lasting 4-5 h with torrential rain occurring at altitudes of 200-600 m. However, in Stage 3 there were continuous generation and dissipation of convection within banded echoes, lasting more than ten hours, with the occurrence of torrential rain mainly below the 300 m altitude. Further analysis on the causes shows that both Stage 2 and Stage 3 had favorable dynamic and topographic conditions, including the exit area of the mesoscale low-level jet, the convergence of southerly and southeasterly winds in the boundary layer, as well as the horn-shaped terrain and windward slopes of the mountains. The difference between two stages is that it was warm-sector torrential rain in the Stage 2, during which the exit area of southern boundary-layer jet was in the northern shallow mountains, the low-level convergence along the mountains was conducive to continuous triggering of convection, and the “train effect” caused the occurrence of extreme torrential rain. While the Stage 3 was influenced by a weak cold air and was related to dynamic convergence on the southern side of a shear line and a mesoscale low vortex. Accordingly, the conceptual model of the July 2025 extreme torrential rain is established.