Meteorological Drought in the Mountainous West

We examine meteorological drought in western North America in the climatic context of the entire continent and adjacent ocean basins. Indices that describe the intensity and spatial extent of dry and wet conditions are computed from station precipitation data at thousands of stations with daily precipitation and temperature observations across North America as well as for geographically specific subsets focusing on the Mountainous West. The evolution of regional drought histories will then be examined in the context of local temperatures over land as well as climatic variability of the Pacific and Atlantic basins as described by dominant sea surface temperature and atmospheric pressure patterns. The strong interdecadal modulation of interannual extremes will be discussed. The relationships between dry, hot, wet and cold conditions will also be described on a regional and seasonal basis. Additionally, we will examine the contribution of daily precipitation extremes to wet and dry year totals as a function of location and season. This will be done for specific extreme wet and dry episodes. By documenting and understanding regional drought relationships with local weather and large-scale climate, we seek to gain insight into the mechanisms that cause drought in the West. We aim especially to understand the causes of the current persistent dry condition and in so doing project the likely future evolution of western North American hydrology.