LAUSR

In southeastern Korea, various synoptic conditions are responsible for heavy rainfall events (HREs) exceeding 30 mmh−1 $\text{mm}\,{\mathrm{h}}^{-1}$ during the Changma, that is, the Korean summer monsoon season. We objectively classify such synoptic patterns of HREs using a self‐organizing map with sea level pressure and 850‐hPa geopotential height fields as input variables. A total of eight synoptic clusters (SCs) are identified. The first three clusters (SC1 − ${-}$ 3), which explain about 18% of HREs, are influenced by tropical cyclones. Excluding minor cluster SC4, SC5 − ${-}$ 8 are dominated by midlatitude weather systems with a southeast‐high or northwest‐low pattern. When examining HREs not influenced by tropical cyclones, SC5 and SC8 show contrasting synoptic patterns. SC5 is influenced by an eastward‐propagating surface low, whereas SC8 is associated with an expansion of the Western North Pacific Subtropical High (WNPSH). In quasi‐geostrophic motion, SC5 exhibits the strongest upward motion, primarily driven by dynamic forcing and diabatic heating. SC8 shows the weakest ascent. Observations show that SC5 is accompanied by widespread nighttime HREs propagating eastward alongside the synoptic system. In contrast, SC8 is accompanied by a localized daytime HRE that propagates northeastward, governed by background southwesterlies along the WNPSH periphery. SC6 − ${-}$ 7 share the synoptic characteristics of SC5 and SC8 but also have distinct characteristics. For example, SC7, which produces intense localized daytime rainfall, is characterized by warm surface and strong upslope winds, indicating terrain‐induced effect with surface heating as a major driver. These results suggest that HREs in southeastern Korea are organized by multiscale processes under various background conditions.