Characteristics and Interannual Variability of Extreme Snowfall Events

Extreme snowfall events provide significant contributions to total snowpack and the characteristics and variability of these events are important for interannual variability in water supply. This study assesses the characteristics of the heaviest snowfall event each winter including average amount, percent of annual snowfall accumulation, coincident mean daily temperature and relationship to ENSO using long-term records from both SNOTEL and National Weather Service Cooperative Network stations across the western United States. Results indicate that the biggest snowfall event of the year can contribute more than a quarter of total annual snowfall water equivalent (SFE) at SNOTEL stations. The size of the biggest snowfall event is strongly positively correlated with annual SFE across the West. ENSO is shown to have a northwest-southwest dipole pattern of correlation with the annual SFE, the size of the biggest event, and the percent of annual SFE contributed by the biggest event. Collectively, this analysis provides a basis for understanding the relative contribution of extreme snowfall events to water resources and provides information on the sensitivity of extreme snowfall events to interannual variability.