Great Lakes ice cover, winter 1971-72

"Thirty-five ice charts were produced from data collected on 23 Lake Survey Center ice reconnaissance flights made in the winter of 1971-72. In addition, five summary ice charts, illustrating ice distribution patterns for short intervals during the winter over the entire Great Lakes, were produced from Lake Survey Center, United States Coast Guard, and Canadian ice reports. Freezing degree-day accumulations indicate that the 1971-72 winter was severe on western Lake Superior and near normal throughout the remainder of the Great Lakes. Ice formation was reported November 10 in western Lake Superior at Duluth Harbor and along the perimeter of all the Great Lakes by the end of January. The period of maximum ice cover varied from the second week of February to the last week of March for individual lakes. During this time maximum ice cover was estimated to be as follows: Lakes Superior and Erie, 95 percent; Lake Michigan, 40 percent; Lake Huron, 70 percent; and Lake Ontario, 20 percent. Ice covers begin to decrease during March. Last reported ice ranged from May 5 for the lower lakes in the Niagara River to June 8 for the upper lakes in western Lake Superior."