The Influence of Atmospheric Circulation on Abnormal Snowpack Melt-Out Events and Drought in Wyoming

Declines in high-elevation snowpack and its effect on water availability in the western United States is of great interest given the projected changes in temperatures that may alter snowpack melt-out timing. Because water from snowmelt is crucial to the West's water supply, this study examines the influence of continental-scale atmospheric variables on snowpack melt out from 1980 to 2016 in Wyoming. Using snow telemetry station and North American Regional Reanalysis data, this research finds abnormally early snowpack melt out in 1987, 1992, and 2012 was associated with persistent above-normal high pressure during spring, leading to sustained warmer-than-normal and drier-than-normal conditions. Conversely, abnormally late snowpack melt out in 2011, 1995, 1983, 1982, 2008, and 1999 was associated with lower-than-normal 500 mb geopotential heights, corresponding to very cold temperatures for April, May, and June, which set the stage for late snowpack melt out. Snowpack melt-out departure values are also correlated with late-season agricultural drought as indicated by 10 Drought Severity indices. Using snowpack melt-out timing, in association with atmospheric variables in a predictive capacity may assist regulatory agencies, such as the Bureau of Reclamation, to make better informed decisions about when, or when not, to store or release water to mitigate late-season agricultural drought impacts.