Regional snowfall impact scale

This paper describes a new regional snowfall impact index that is being produced operationally on an experimental basis by NOAA's National Climatic Data Center. The Regional Snowfall Impact Scale (ReSIS) is based on the spatial extent of the storm, the amount of snowfall, and the juxtaposition of these elements with population. Including population information ties the index to societal impacts. ReSIS is an evolution of the Northeast Snowfall Impact Scale (NESIS) which NCDC began producing operationally in 2005. While NESIS was developed for storms that had a major impact in the Northeast, it includes the impact of snow on other regions as well. It can be thought of as a quasi-national index that is calibrated to Northeast snowstorms. By contrast, ReSIS is a regional index; a separate index is produced for each of six climate regions in the eastern two-thirds of the nation. The methodology for computing ReSIS, which requires region-specific parameters and thresholds, is explained. The new index has been calculated for about 500 snowstorms that occurred between 1900 and 2010, including the 50 largest snowstorms in each of the six eastern climate regions. This allows ReSIS to put snowstorms into a century-scale historical perspective. Several seasons will be examined in detail to show the operational impact of calculating the index in near-real time and the seasonal variability of snowstorms. Also, the GIS Snowstorm Database, which serves as input to ReSIS, is briefly described.