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Raymond A. Assel


General regional and temporal trends in maximum freezing degree-days (FDD's) are identified for the shore zone of the Great Lakes Basin for the 80 winter periods 1897–1977. The cumulative frequency distribution of FDD's at cub of 25 locations is used to define winter severity for the 80 winters. Graphs, contour maps and tabulations are used to summarize and portray the spatial and temporal distribution of FDD's and mild and severe winter categories of winter severity.

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Raymond A. Assel, C. Robert Snider, and Reginald Lawrence


Winter 1983 was one of the mildest winters in the past 200 years. One result of the unusual winter weather was the mildest overall ice season on the Great Lakes since systematic observations of ice cover extent on the Lakes were initiated some 20-odd years ago. The 1983 winter developed during the peak of one of the most intense El Niño-Southern Oscillation events of this century. Associated with the mild temperatures in the United States was an extremely strong Aleution low that persisted most of the winter. Monthly Northern Hemispheric circulation patterns were generally weak; no general long wave patterns were able to persist; and 700 mb heights were above normal. Annual maximum ice coverage on the Great Lakes was much below normal: Lake Superior 21% (normal is 75%), Lake Michigan 17% (normal is 45%), Lake Huron 36% (normal is 68%), Lake Erie 25% (normal is 90%), and Lake Ontario less than 10% (normal is 24%). Economic impact of the below-normal ice cover included reduced U.S. Coast Guard ice breaking assistance to commercial vessels, reduced U.S. Coast Guard flood relief operations in connecting channels of the Great Lakes, and virtually no ice-related winter power losses at hydropower plants on the St. Marys, Niagara and St. Lawrence Rivers.

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