Idealized large-eddy simulations (LES) are used to examine lake-mountain effects on clouds and precipitation over the Tibetan Plateau (TP) under conditions of low air density and limited moisture. This study conducts LES respectively with lake-only, mountain-only, and combined lake-mountain configurations. The alpine lake alleviates key constraints on convective organization by enhancing low-level moisture and reducing thermodynamic inhibition to convective initiation. However, in this energy- and moisture-limited environment, the lake alone induces only shallow ascent, sustaining shallow convection and weak precipitation with limited deepening. By contrast, mountain alone provides mechanically forced uplift, but the scarcity of moisture over the TP confines precipitation to a narrow area near the mountain. With combined lake-mountain configurations, lake-supplied moisture is lifted by the downstream mountain, deep convective clouds develop, yielding strong and extensive precipitation. Notably, mountains exhibit a reversed role in lake-mountain interactions affecting clouds and precipitation processes, owing to the competition between orographic lifting and blocking effects. High mountains enhance precipitation on the upstream side while suppressing downstream development by restricting low-level moisture transport from lake source, whereas low mountains allow broader horizontal moisture advection but induce weaker vertical development. Overall, lake-mountain coupling is intrinsic to the TP’s high-elevation, moisture and energy limited environment, where lake-driven moistening lowers initiation barriers, orographic lifting and blocking organize and deepen convection, and mixed-phase processes further reshape precipitation patterns, a pathway that is typically not dominant over the plains. These findings clarify how high-elevation surface heterogeneity affects clouds and precipitation, with implications for the Asian water cycle.