Benjamin Hatchett , Daniel McEvoy

Snow droughts are commonly defined as below average snowpack at a point in time, typically 1 April in the western United States. This definition is valuable for interpreting the state of the snowpack for resource management but obscures the temporal evolution of snow drought. Borrowing from dynamical systems theory, we applied phase diagrams to visually examine the evolution of snowpack conditions in maritime, intermountain, and continental snow climates in the western United States using station observations as well as spatially distributed estimates of snow water equivalent (SWE) and precipitation. Phase diagrams of observed SWE and precipitation percentiles highlighted snow drought onset, evolution, and termination timing at daily timescales using a percentile-based drought definition. A web tool for this visualization approach is presented that allows users to create real-time or historic phase diagrams. The goal of this tool is to facilitate the communication of snow drought conditions to broader audiences, especially in years characterized by notable hydroclimate variability and/or extreme events. Spatially distributed estimates of daily precipitation and SWE highlighted regional and elevation-dependent variability in snow drought type and extent. When combined with additional data such as streamflow, phase diagrams and spatial estimates of snow drought conditions can inform drought monitoring and early warning as well as to help link snow drought type and evolution to observed impacts on ecosystems, water resources, and recreation.