Relationship between atmospheric circulation and snowpack in the western USA

Snow anomalies in the western USA have a significant impact on water availability, and hence have been widely investigated by many researchers. This study focuses on how anomalous atmospheric circulation affects snowpack accumulation in the western USA. Our results indicate that the mid-latitude atmospheric circulation anomalies induced by the El Nino–Southern Oscillation (ENSO) tend to drive winter precipitation shifts, leading to an anomalous snowpack distribution in the western USA. The warm phase of ENSO produces increased snowpack in the Southwest, whereas the cold phase generates increased snowpack in the Northwest. The results also indicate that temperature has a secondary impact on the anomalous snowpack distribution during ENSO episodes. Additionally, the atmospheric internal variability-related Pacific–North American (PNA) pattern is found to affect snow anomalies strongly in the western USA independent from ENSO. The positive phase of the PNA pattern produces colder temperature and stronger precipitation due to the lower pressure in the region, leading to an above-average snowpack. Conversely, the negative phase of the PNA pattern generates warmer temperature and weaker precipitation resulting from the higher pressure, producing below-average snowpack in the western USA. The significant findings that result from this study strengthen our understanding of climate and water supply variability in the western USA. Copyright © 2006 John Wiley & Sons, Ltd.