A method for indexing snow depth based on the variability of valley precipitation and temperature was used. This created a snow index for NW Otago for the period 1930-1991. An empirical model using daily precipitation and temperature data was not successful in reproducing the variable nature of a mountain snowpack. Synoptic weather patterns were analysed using the snow index. High snow depth winters were related to seasons with anomalous north west, southwest and southerly airflow. Indices for the southern oscillation, sunspot numbers, and stratospheric quasi-biennial oscillation were compared with the snow index. Significant correlations were found with the sunspot cycle and the stratospheric QBO index. Possible precursor conditions for high snow depth winters are identified. Forecasting winter snow depth is discussed.