Predicting snowpack using the Southern Oscillation Index

The El Nino-Southern Oscillation phenomenon is a known factor influencing the climate and streamflow patterns in the western United States. Previous studies have incorporated the Southern Oscillation Index (SOl) into statistically-based streamflow forecast procedures. This paper highlights some problems those studies have identified and discusses a new forecast procedure. Since the majority of the water supply in the Northwest starts as snow in the mountains during the winter months, snow water equivalent (SWE) is used as the dependent variable in this new non-statistical forecast procedure. This procedure uses the SOl to predict seasonal precipitation as measured by SWE at a designated site. The SOl data through June is used in mid-July to prepare a forecast of the October through December snow accumulation. Similarly, the SOl data through September is used in mid- October to prepare a forecast of the January through March snow accumulation. The procedure compares the changing SOl over time to historical SOl and SWE patterns. The results show that it is possible to predict future SWE for the Vienna Mine Snotel site in southern Idaho using current year SOl data. The forecast would be for 'near-average,''above near-average,' or 'below near-average' snow accumulation during the period.