The western U.S. derives its water resources predominantly from cold season precipitation and storage in snowpack along the narrow Cascades and Sierra ranges, and the Rocky Mountains. Hydroclimate is modulated by the diverse orographic features across the region. Predicting the meteorological and hydrologic conditions in mountainous regions is challenging because both precipitation and snow are strongly affected by the complex orography. This paper will describe numerical experiments using a regional climate model driven by global reanalyses, global climate models, and seasonal climate and extended weather forecasts to examine a number of modeling issues including the effects of model resolution, physics parameterizations, and large-scale conditions on simulating the hydrometeorological processes of the western U.S. In addition, comparisons will be made between different dynamically and statistically downscaled meteorological conditions and their impacts on simulating the hydrology of river basins.