Great Lakes ice cover, winter 1969-70

"Thirty-three ice charts were produced from data obtained on 14 visual aerial reconnaissance flights made during the 1969-70 ice season. Winter temperatures were classified as below normal and were determined from freezing degree-day accumulations. Reported dates of first ice varied from November 3, 1969, on southern Lake Huron to December 23, 1969, on eastern Lake Ontario. The period of maximum ice cover varied across the Great Lakes, as did the areal extent of the ice cover. During the periods of maximum ice extent, Lake Superior was estimated to be 85 percent covered, with a particularly heavy concentration of winter ice in the southeastern portion; Lake Michigan 30 percent covered, with heavy winter ice confined to the northern end of the lake, and various concentrations of drift ice along the lake perimeter; Lake Huron 50 percent covered with differing concentrations around the lake except for the central basin; Lake Erie 95 percent covered with most of the winter ice containing a drifted snow cover; and Lake Ontario 15 percent covered with the major concentrations located in the approaches to the St. Lawrence River. The reported dates of last ice ranged from March 31 at Tibbetts Point on eastern Lake Ontario to April 27 at Point Iroquois on eastern Lake Superior."