NOAA TM NOS LSCD 1 f f JOAA Technical Memorandum NOS LSCD 1 U. S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration GREAT LAKES ICE COVER WINTER 1968-69 LAKE SURVEY MARINE and earth CENTER SCIENCES LIPPARY &CT 2 1973 Federal Building, Detroit, Mich. U~ S~ PeP'- Com: October 1971 £6 /7?f.y U. S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration 1 National Ocean Survey NOAA Technical Memorandum NOS LSCD 1 GREAT LAKES ICE COVER WINTER 1968-69 Donald R. Rondy f Lake Survey Center Limnology Division, Federal Building Detroit, Michigan October 1971 (3 5618 CONTENTS Page LIST OF TABLES AND FIGURES iii ABSTRACT 1 INTRODUCTION i DATA COLLECTION Aerial Observations 2 Shore Observations 2 Freezing Degree-days 2 WINTER CHARACTERISTICS 3 DATA PRESENTATION Ice Charts 4 Ice Summary Charts 4 DISCUSSION Lake Superior 5 Lake Michigan 6 Lake Huron 8 Lake St. Clair 9 Lake Erie 10 Lake Ontario 11 ACKNOWLEDGEMENTS 12 ii LIST OF TABLE AND PLATES TABLE 1 Key to Ice Chart Symbols PLATES 1 Accumulated Freezing Degree-days--Lake Superior 2 Accumulated Freezing Degree-days--Lake Michigan 3 Accumulated Freezing Degree-days--Lake Huron 4 Accumulated Freezing Degree-days--Lake Erie 5 Accumulated Freezing Degree-days--Lake Ontario 6 Maximum Ice Cover-Southern Lakes 7 Maximum Ice Cover-Northern Lakes 8 Breakup Patterns 9-11 Ice Charts--Lake Superior 12-16 Ice Charts--Whitefish Bay 17-19 Ice Charts--St. Marys River 20-22 Ice Charts--Straits of Mackinac 23-24 Ice Charts--Lake Michigan 25 Ice Chart--Lake Huron 26-28 Ice Charts--Lake St. Clair 29-31 Ice Charts--Lake Erie iii GREAT LAKES ICE COVER WINTER 1968-69 Donald R. Rondy Department of Commerce NOAA, National Ocean Survey Lake Survey Center Detroit, Michigan ABSTRACT Twenty-three ice charts were produced from data collected on eight reconnaissance flights made during the 1968-69 winter ice season. Ice formation was first reported on December 9, 1968. Areas reporting extended from Duluth, Minnesota, on western Lake Super­ ior, to Barcelona, New York, on the south shore of Lake Erie. Winter temperatures generally varied from slightly above normal in the Lake Superior region to slightly below normal on Lake Erie. During the period of maximum ice cover, 40 percent of the surface of Lake Superior was covered. More than half the ice was concentrated in the Apostle Islands-Duluth-Isle Royale areas at the western end of the lake. Lake Michigan was 15 percent covered with the ice confined mostly to the north end of the lake and Green Bay. Lake Huron contained a maximum 50 percent ice cover with winter ice in the North Channel, the Straits of Mackinac, and Saginaw Bay. Lake Erie was 80 percent ice covered, with heavy winter ice concentrated along the southern and eastern shores. The mid-lake area contained brash and small floes. At maximum, Lake Ontario was estimated to be 10 percent covered, with the ice concentrated in the northeastern end of the lake. The last report of ice in the Great Lakes was from the Buffalo area of Lake Erie on May 2, 1969. INTRODUCTION The aerial ice reconnaissance program of the Lake Survey Center began in 1963. It is part of a total plan to obtain data on the physical pheno­ mena of the Great Lakes. The purpose of the ice program is to gain an un­ derstanding of the formation, distribution, and decay of the ice cover on the Great Lakes and their connecting waters. The data are presented in the form of ice charts covering the individual lakes and specific areas on those lakes. Accumulations of freezing degree-days were used as an index to determine the severity of the winter and to aid in scheduling the re­ connaissance flights. As the ice season progressed U. S. Coast Guard ice messages and reports made by Lake Survey Center water level gage observers were also used as flight scheduling aids. This report presents data collected during the 1968-69 visual aerial ice reconnaissance program and summarizes the winter ice and weather condi­ tions for the season. Ice cover reports have been prepared for each winter since 1962-63 and are available from the Lake Survey Center. 1 DATA COLLECTION Aerial Observations Ice cover characteristics were charted in symbolic form from U. S. Coast Guard aircraft flying at altitudes of up to 9000 feet (2740 m). Ice information was plotted on work sheets, while detailed verbal descriptions were recorded on magnetic tape to aid the observer in a later compilation of the ice charts. The flights began on February 4, 1969, and continued at weekly intervals through April 3, 1969. Approximately 6200 miles (9900 km) and 40 hours of flight time were logged during the season. The dates of the reconnaissance flights and the areas covered are given below. ICE RECONNAISSANCE FLIGHTS - WINTER 1968-69 FLIGHT DATE AREA COVERED 1 February 4, 1969 Lakes St. Clair, Erie 2 February 13 Straits of Mackinac Area, Lake Superior 3 February 25 Lakes St. Clair, Erie 4 March 4 Straits of Mackinac Area, Whitefish Bay, Lakes Huron, St. Clair 5 March 11 Straits of Mackinac Area Lake Superior 6 March 22 Lakes St. Clair, Erie 7 March 27 Straits of Mackinac Area, Lake Superior 8 April 3 Straits of Mackinac Area, Whitefish Bay Shore Observations Lake Survey water level gage observers reported daily ice conditions throughout the winter. This information was used to monitor ice conditions and to locate general areas where ice first formed and where it was last to leave. Freezing Degree-days The accumulation of freezing degree-days is a commonly used index of 2 winter severity. A freezing degree-day is defined as a day with mean temperature one degree below 32°F (0°C). For example, a day having a mean temperature of 27°F (-3°C) would equal five freezing degree-days. Many other limnological and meteorological factors affect ice formation and growth, however certain relationships have been established between freezing degree-days and ice cover distribution. The daily mean air temperature from six National Weather Service meteorological stations on the Great Lakes were used to determine the accumulation of freezing degree- days for each lake. The stations used v/ere Duluth, Minnesota; Sault Ste. Marie, Michigan; Green Bay, Wisconsin; Alpena, Michigan; Cleveland, Ohio; and Rochester, New York. Graphs of accumulated freezing degree-days ver­ sus time were plotted for each of the stations (Plates 1 through 5). The curve of the long-term mean is shown so that determinations can be made of relative winter severity, and the approximate date of maximum degree-day accumulation, and the approximate date of maximum ice cover. The greatest areal extent of ice cover seems to occur just prior to the maximum freezing degree-day accumulation. The flight dates and the accumulated freezing degree days for the per­ iod November through April are shown on Plates 1 through 5. Temperature data were obtained from the Weekly Weather and Crop Bulletin published by the U. S. Department of Commerce. WINTER CHARACTERISTICS The 1968-69 winter temperature patterns varied from slightly above normal in the north to slightly below normal in the south. Temperatures for Lake Superior and northern Lake Michigan were above normal, as shown by the low accumulation of freezing degree-days recorded at Sault Ste. Marie and Green Bay (Plates 1 and 2). Temperatures for Lakes Huron and Erie were below normal, as shown by the relatively large accumulation of freezing degree-days recorded at Alpena and Cleveland (Plates 3 and 4). The freezing degree-day curve for Rochester, however, appeared to follow the long-term mean (Plate 5). The early winter period also saw a number of meteorological stations record their greatest snowfall. Temperatures for November and the first part of December were generally above normal across the Great Lakes area. The temperatures for the whole month of December, however, generally averaged 2°F below normal. The low monthly temperature was the result of persistent and extremely low daily temperatures during the last two weeks of the month. By the week ending December 29, temperatures had dropped to as much as 8°F below the normal of 12°F (-11°C) at Duluth, and 10°F below the normal of 18°F (-8°C) at Sault Ste. Marie. December also brought heavy snowfall to parts of Minne­ sota, Wisconsin, and upper Michigan. Green Bay, Wisconsin, reported 26.7 inches (67.8 cm) of snowfall, highest since 1887; Alpena, Michigan, 35.2 inches (89.4 cm), highest in 81 years and second highest on record; and Marquette, Michigan, 41.1 inches (104.4 cm), the heaviest in 58 years. Low temperatures during the last two weeks of December are indicated by the steep upward slope of the freezing degree-day curves for all of the 3 stations (Plates 1 through 5). Low temperatures continued into January, and for the week ending January 5, ranged from -7°F (~22°C) at Duluth, Minnesota, to 16°F (-9°C) at Cleveland, Ohio. Cold weather predominated during the first half of January. Warmer weather prevailed during the last half, causing temperatures for the month to range from normal in the northern half of the basin to 2°F below normal in the southern half. January snowfall was the highlight of the month with Duluth, Minnesota accumulating 46.8 inches (118.9 cm) of snow, great­ est for any month since 1917; and Marquette, Michigan, with a snowfall of 29.5 inches (74.9 cm) the fourth heaviest in 40 years. February temp­ eratures averaged 3° above normal across the Great Lakes with precipitation at record lows.