A Case Study of Large Snowfall Event Variability in the Upper Colorado River Basin

With the recent decline in overall mountain snowpack across the western United States, large and episodic snowfall events are often representing larger proportions of seasonal snow accumulation. As alpine snow serves as the primary source of water for many basins throughout the west, including the Upper Colorado River Basin (UCRB), expanding our understanding of the spatiotemporal characteristics of large snowfall events, their associated atmospheric forcings, and their trends over time, is needed to improve services such as seasonal forecasting and drought monitoring.

This study examines snowfall event frequency and intensity, as measured at snow telemetry (SNOTEL) in-situ mountain instrument sites, during recently observed wet and dry years (e.g. 2011 and 2002, respectively) in the UCRB. Characteristics in event magnitude are spatiotemporally assessed across the sub-basins of the UCRB, with particular regard to total snow-water equivalent as an indicator of basin water supply. The trends in large snowfall event frequency over recent years are also assessed as indicators of regional climate variability.

A case study of specific large snowfall events then focuses on the atmospheric forcings of each event through a synoptic examination of surface and upper atmospheric dynamics. Factors such as moisture delivery mechanisms (e.g. atmospheric rivers), storm tracks, and atmospheric-oceanic teleconnections (e.g. ENSO, PDO) are also identified as contributors in determining event intensity and duration.