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While the Fujita and Saffir-Simpson Scales characterize tornadoes and hurricanes, there is no widely used scale to classify snowstorms. The Northeast Snowfall Impact Scale (NESIS) was developed by Paul Kocin of The Weather Channel and Louis Uccellini of the National Weather Service to characterize and rank Northeast snowstorms. NESIS has five categories; Extreme, Crippling, Major, Significant, and Notable. The NESIS is not only based on snowfall amount, but also aerial extent and population affected. Thus NESIS is an effective measure of a storm's societal impacts. Some of the GIS computational issues encountered while calculating NESIS include quality control, development of a robust population density grid, and selection of an appropriate spatial interpolation scheme. All of the geoprocessing tasks are done with scripts and models. This paper describes the different methodologies used to calculate NESIS, examines differences between methodologies, techniques to minimize the differences, and recommends procedures for calculating NESIS operationally beginning with the 2005-06 winter season.