The objective of this study is to provide an evaluation of the magnitude of apparent temperature and the weather stress index (WSI) in winter across the United States. In addition, two extremely cold winters, 1976–77 and 1981–82, are analyzed in terms of their relative severity with the assistance of the WSI.

Mean apparent temperatures around the nation for 0300 LST in January show an expected latitudinal trend, with the lowest apparent temperatures found in the north central United States. Although this distribution roughly approximates that of mean air temperature for January, there are significant differences. Large disparities between mean 0300 LST apparent temperature and air temperature exist from Kansas to Minnesota. Much-smaller disparities are found in the East and the South, heightening the latitudinal gradient for apparent temperature. The severity of winter conditions in the north-central United States is clearly noted when evaluating the WSI; in parts of North Dakota and Minnesota, the apparent temperature corresponding to the 99-percent WSI at 0300 LST is below −45°C.

The winter of 1981–82 is credited as having the most-severe individual winter day since 1948. On 11 January 1982, WSI values exceeding 99 percent covered over two-thirds of the nation. However, based on the duration of stressful weather conditions, the winter of 1976–77 was more stressful than 1981–82. During 1976–77, the most-stressful conditions were encountered in the populous East, and in a sizable area over one-third of the days were described as stressful (WSI exceeding 90 percent). These proportions were much lower during the winter of 1981–82.

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1 Center for Climatic Research, University of Delaware, Newark, DE 19716.

2 Department of Geography, University of Delaware, Newark, DE 19716.