Abstract
In the western United States, seasonal snow accumulation largely determines water resource availability. Natural climate variability and anthropogenic climate change present challenges to water managers who must distribute a highly allocated water supply to satisfy many competing objectives. Extreme snowfall events are found to contribute 20-38% of annual snowfall water equivalent (SFE) and shape nearly 70% of interannual variability in annual SFE on average. By midcentury, increasing temperatures are projected to decrease the size of extreme snowfall events and the portion of annual SFE contributed by these events. Projected increases in the interannual variability of extreme snowfall events are expected to enhance interannual variability in annual SFE, resulting in less and more variable snowfall in the future. We present a SFE analysis tool that utilizes the strong relationships between annual SFE and extreme events to provide probabilistic guidance for seasonal SFE forecasts.