A pervasive 20–30 yr periodicity is observed in stable oxygen isotope values over the past 1000 yr from varved lacustrine calcite obtained from Fayetteville Green Lake, New York. Correlation analysis between historical oxygen isotope values and winter vortex latitude shows an inverse relationship wherein an expanded vortex is associated with high δ18Ocalcite values, and vice versa. An expansion of the vortex favors advection of cyclones from the Gulf of Mexico and the Atlantic regions characterized by high δ18Oprecipitation values, whereas a contracted vortex favors the development of cross-continental storms originating in the Pacific, which preferentially rain out 18O as they propagate eastward. We hypothesize that changes in the size of the winter vortex every 20–30 yr over the past 1000 yr modify the primary source regions for meteoric precipitation. We propose two possible climate forcings to explain our hypothesis: an external forcing related to solar variability and an internal forcing related to ocean-atmosphere links.