We analysed the impact of a summer snow accumulation event linked to an atmospheric river in central Chile. Using observational and remote sensing data, we show that accumulation prevails in all the glaciers of the Maipo River basin, and this sole event defines the fact that the Olivares Alfa glacier mass balance was close to equilibrium despite it being a dry year. This demonstrates that an unseasonal accumulation event can counteract the seasonal trends affecting subtropical Andean glaciers.