The Northwest's climate and water resources respond to variations in the atmosphere/ocean system over the Pacific Ocean. Variations in the tropics (El Nino-Southern Oscillation, or ENSO) and in midlatitudes (Pacific Decadal Oscillation, or PDO) have comparable influence on the Northwest, with warm-phase ENSO or warm-phase PDO years being more likely to see above-average temperatures, and below-average precipitation, snowpack, streamflow, and likelihood of flooding. For example, the Columbia River's naturalized flow at The Dalles is, on average, 21% higher during cool-phase ENSO years than during warm-phase ENSO years, and is 44% higher during years when both ENSO and PDO are in cool phase than when both are in warm phase. This apparent reinforcement occurs even though ENSO and PDO are not statistically independent. Taken together, ENSO and PDO are important measures in forecasting regional water resources and are gaining recognition in water resources forecasting efforts.