A scaled index of winter severity

A procedure for indexing the severity of a winter would be helpful to wildlife managers and general public in understanding how mild or how severe conditions are for any given season or month. The Scaled Index of Winter Severity (SIWS), has a scale from -4.0 for most severe to +4.0 for mildest with 0 being near a normal winter. The index uses minimum daily temperatures, snow depth, snow water equivalent, snow density and precipitation accumulation (or SWE), above or below a threshold level. The weightings and threshold for each parameter can be changed to represent different species. Stations can be accumulated or weighted to represent winter range areas. Months can be looked at individually or accumulated for a season. Depending on the area, summer growth on winter ranges may also be a factor affecting winter severity.Frequency analysis of data provides probability of nonexceedance that is used to determine the level of any given component or combined components for the winter severity index.Trends of SIWS for a portion of Yellowstone National Park for the past 40 years is presented.