To improve our understanding of paleoclimatic records in the southwest Yukon, we examined controls on precipitation del18O using an isotopically-equipped general circulation model. Our results show that, particularly during the cool-season, elevated del18O is associated with a deeper Aleutian Low and stronger southerly moisture flow, while lower del18O is associated with the opposite meteorological conditions. These results suggest that the large mid-19th century shift towards lower del18O values seen in paleoclimate records from the region was associated with a shift towards a weaker Aleutian Low. While in disagreement with a previous interpretation of this shift, it is consistent with records of glacial advance and tree-ring growth during the same period, and observational studies of Aleutian Low controls on temperature and precipitation in the region.