The Water Year 2015 Snow Drought in Washigton State: What Does It Tell Us About Future Drought Risk?

In many locations across the Washington State, the 2015 water year exhibited some of the lowest snow accumulations in the observational record. The low snowpack conditions, both in the Cascades and more broadly across the Northwest, set the stage for summer drought conditions that had negative impacts on water supplies, especially for agriculture, ecosystem health, and hydroelectricity production.  
This paper presents data from SNOTEL stations throughout the Washington Cascades, illustrating the pervasiveness of low-snowpack conditions for the 2015 water year. Based on the SNOTEL records and observations of temperature and precipitation at meteorological stations in the region, it is clear that temperature was the driver of low-snowpack conditions, with a large proportion of the winter precipitation being delivered via atmospheric river events with high freezing levels.   
Comparison of the seasonal temperature anomalies to future projections shows that the 2015 water year is a good analog for average temperatures around the mid-21st century. At the same time, aspects of the atmospheric circulation that helped contribute to the anomalous warmth and the paucity of cold storms resemble recognizable patterns of natural atmospheric circulation variability. The particular pattern evident in the 2015 water year (the Pacific North American pattern) is likely to continue to play an important role in the interannual variability of snowpack.   
Information about future climate often focuses on changes that are tied to forcing from greenhouse gas emissions, and omit information about interannual circulation variability. Given that 2015 illustrates the important role that this variability can play in contributing to snow conditions, the paper recommends a more integrated approach when communicating to water managers about future 21st century snowpack conditions.  (KEYWORDS: drought, climate change, Washington State, atmospheric river, 2015)