Great Lakes ice atlas

"A series of 33 charts is presented to illustrate the ice cover on the Great Lakes for three classifications of winter: mild, normal, and severe. Six ice charts are presented for each of the Great Lakes. Two charts show the maximum extent of ice cover during a mild and a severe winter and four charts illustrate the characteristic patterns and extent of the ice cover throughout a winter classified as normal. The percent of lake surface area that can be expected to become ice covered during a normal winter is: 60 percent Superior, 40 percent Michigan, 60 percent Huron, 95 percent Erie, and 15 percent Ontario. Mid-winter ice thicknesses can range from 36 in. (91 cm) along the north shore of Lake Superior to 4 in. (10 cm) during a mild winter on the lower lakes."