Exploratory Analysis of Snowpack in Washington State

Snow water equivalent (SWE) is used to measure seasonal snowpack accumulations. The annual maximum SWE and the rate of snowpack accumulation and melt-off determine the volume of spring runoff. In this paper, the objective is to use exploratory analysis to investigate the effect of variation in El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on the annual maximum SWE and its associated timing. Traditionally, snowpack was thought to peak around April 1 in the Pacific Northwest. Twenty-five snowpack telemetry (SNOTEL) sites that have more than 20 years of daily records in Washington State were examined first. It was also found that the peaks of snowpack do not occur ten days before and after April 1 in most SNOTEL sites. Then Pearson's correlation coefficient test was applied to examine the relationship between last year's ENSO indices and the current annual maximum SWE and its associated timing for each site. Finally, a simple linear regression model was used to analyze the combined effects of ENSO and PDO as well as their interaction on the annual maximum SWE. Teleconnections between these indices and the annual maximum SWE in Washington State were identified by the exploratory analysis.