Graduation date: 2007The physical controls of snowmelt in the Pacific Northwest (PNW) are poorly understood. While there have been numerous field and modeling investigations at the plot and watershed scale, few studies have identified how the snow energy balance (EB) components vary in importance both spatially and temporally. The identification of how dominant EB components vary in space and time will allow us to understand how the snow regime will be affected by environmental change. We apply two physically based snow energy balance models (SNOBAL and ISNOBAL) to two different climate regimes of PNW Cascade Mountains to investigate the spatial and temporal variability of EB components which cause snowmelt. We found that radiation dominated the EB in both the rain-on-snow, Western Cascades environment and in a semi-arid watershed in the Eastern Cascades. Turbulent energy exchanges varied with topographic position, vegetation, and most importantly wind speed. In both modeling scenarios warmer winters led to shallower snowpack accumulation. Shorter snow seasons resulted in lower radiation inputs and higher sensible heat exchanges in the annual EB. Numerical simulation of snowmelt processes has helped to provide an understanding of the anticipated effects of environmental change on the snow regime in the PNW.