Technical Abstract: Erosion on non-irrigated cropland of the northwestern USA is largely the result of winter rainfall and snowmelt events and frequently involves thawing soil. Conservationists and land managers need erosion models that predict the occurrence and severity of these winter events as well as the influence of crop management. Winter conditions in the northwestern USA are particularly difficult to model because of the transient nature of the freezing and thawing process. The USDA-Water Erosion Prediction Project (WEPP) model is capable of estimating spatial and temporal distributions of soil loss. The WEPP model is based on fundamental hydrologic and erosion processes, including major components for climate, infiltration, water balance, crop growth, residue decomposition, surface runoff and erosion. The model includes winter routines developed specifically for areas where soil freezing and thawing affects runoff and erosion. The model must be tested and parameter values optimized for the wide range of conditions to which it will be applied. Eight years of runoff plot data under various crop managements at the Palouse Conservation Field Station (PCFS) near Pullman, WA were available for evaluating WEPP. The model predicted runoff for only 12% of the observed events when permeability was set internally by the model. Therefore, the model was run using the lowest permeability value it would accept. These results still underpredicted the observed runoff on an individual storm basis, indicating additional investigation and testing is needed.