We analyzed the chronologies of cellulose stable isotopes (δ¹³C and δ¹⁸O) and tree-ring widths from European larch (Larix decidua) in a high-altitude site (2190 m a.s.l.) at the bottom of a glacial valley in the Italian Alps, and investigated their dependence on monthly meteorological variables and δ¹⁸O precipitation values. The δ¹⁸O of tree-ring cellulose appears to be strongly driven by the δ¹⁸O of winter snowfall (November to March), which suggests that larch trees mostly use the snow-melt water of the previous winter during the growing season. This water, which also comes from the slope streams and from the underground flow of nearby steep slopes, infiltrates the soil in the valley bottom. The tree-ring cellulose δ¹⁸O values were also found to be influenced by the August precipitation δ¹⁸O and mean temperature. The associated regression model shows that the δ¹⁸O chronology from the tree rings explains up to 34% of the variance in the winter precipitation δ¹⁸O record, demonstrating the potential for reconstructing the δ¹⁸O isotopic composition of past winter precipitation in the study region. Unlike most other tree-ring studies that focus on growing season signals, in our study the summer signal was small and the winter signal dominant due to the special conditions of the glacial valley. Site topography, geomorphology and soil characteristics in particular influence the stable isotope signal in tree-ring cellulose.