NOAA TM NOS LSC D 3

A UNIT DEPAR COM OAA Technical Memorandum NOS LSC D 3

t . S. DEPARTMENT OF COMMERCE r ational Oceanic and Atmospheric Administration f i ational Ocean Survey

Great Lakes Ice Cover Winter 1969-1970

ANO~*EA$fH SCIENCES LIBRARY

0013 1973 Lake Survey Center M.O.A.A. U. S. Dept, of Commerce DETROIT, MICH.

March 1972 f LSC Technical Memoranda Ice Cover Winter 1969-70. Donald R. Rondy, October 1971. Lake Survey Center 1972 Research Program January 1972. c-e l7 , U. S. DEPARTMENT OF COMMERCE mV70 National Oceanic and Atmospheric Administration National Ocean Survey

NOAA Technical Memorandum NOS LSC D 3

GREAT LAKES ICE COVER

WINTER 1969-70

Donald R. Rondy

f

Lake Survey Center Limnology Division Federal Building Detroit,

March 1972

73 5621 CONTENTS

Page

LIST OF TABLES AND PLATES iii

ABSTRACT 1

INTRODUCTION 2

DATA COLLECTION 2

Aerial Observations 2

Shore Observations 3

Freezing Degree-days 3

WINTER CHARACTERISTICS 4

DATA PRESENTATION 5

Ice Charts 5

Ice Summary Charts 5

DISCUSSION 5

Lake Superior 5

Lake Michigan 7

Lake Huron 9

Lake St. Clair 10

Lake Erie 11

Lake 13

ACKNOWLEDGEMENTS 13

ii LIST OF TABLES AND PLATES

TABLES

1 Key to Ice Chart Symbols

Plates

1 Accumulated Freezing Degree-days—

2 Accumulated Freezing Degree-days—

3 Accumulated Freezing Degree-days—

4 Accumulated Freezing Degree-days—

5 Accumulated Freezing Degree-days—

6 Maximum Ice Cover-Southern Lakes

7 Maximum Ice Cover-Northern Lakes

8-12 Ice Charts—Lake Superior

13-19 Ice Charts—Whitefish Bay

20-24 Ice Charts—St. Marys River

25-29 Ice Charts—

30-31 Ice Charts—Lake Michigan

32-33 Ice Charts—Lake Huron

34-37 Ice Charts—Lake St. Clair

38-40 Ice Charts—Lake Erie

iii GREAT LAKES ICE COVER - WINTER 1969-70

by

DONALD R. RONDY

DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Survey Lake Survey Center Detroit, Michigan

ABSTRACT

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 per­ cent 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.

1 INTRODUCTION

Ice cover data have been acquired since February 1963, as a part of an overall program to obtain information on the physical phenomena of the Great Lakes. These data are presented in the form of ice charts covering individual lakes and selected areas. The freezing degree-day concept of classifying the winter severity was used as an aid in scheduling the initial reconnaissance flights. U. S. Coast Guard ice messages and ice reports from the Lake Survey Center water level gage observers were used as flight planning aids later in the season.

This report presents data collected during the 1969-70 aerial ice reconnaissance program, and summarizes the winter ice and weather conditions. Ice cover reports have been prepared for each ice season since the winter of 1962-63 and are available from Lake Survey Center.

DATA COLLECTION

Aerial Observations

The ice cover characteristics were mapped from aircraft flying at altitudes ranging up to 9,000 feet (2740 m). Limits of the areal distribution of the various ice concentrations were plotted on work sheets, while detailed descriptions were recorded on magnetic tape. The taped information was useful in later compilation of the ice charts. Flights began on February 17, 1970, and continued at weekly intervals through March 31, 1970. Approximately 6200 miles (9500 km) and 40 hours of flight time were logged. Two supplementary heli­ copter flights were made, originating at the Coast Guard Air Station, Selfridge Air Force Base. In addition to the Lake Survey flights four operational flights were made by the U. S. Coast Guard from the air station at Traverse City, Michigan.

The dates of the reconnaissance flights and the areas covered are listed below:

ICE RECONNAISSANCE FLIGHTS - WINTER 1969-70

FLIGHT NO. DATE AREA

1 February 17 St. Clair, Erie

2 February 25 Straits of Mackinac, Whitefish Bay St. Marys River

3 March 5 St. Clair, Erie

4 March 10 Michigan

2 flight no. DATE AREA

5 March 11 Huron, St. Clair

6 March 17 Superior, St. Marys River

7 March 24 Superior, Straits of Mackinac, St. Marys River

8 March 31 St. Marys River

Supplementary helicopter flights:

February 24 Erie

March 17 St. Clair, southern Huron

Coast Guard operational flights:

February 6 St. Marys River, Straits of Mackinac, Whitefish Bay

April 1 Superior

April 3 Superior, northern Michigan

April 10 Superior

Shore Observations

Forty-one water level gage observers reported ice conditions daily throughout the winter. The shore station information was primarily used to locate areas of first ice formation, to monitor conditions during the season, and to pinpoint areas where ice was retained the longest.

Freezing Degree-days

The accumulation of freezing degree-days is a useful index for estimating winter severity. A freezing degree-day is defined as a day having a mean temperature one degree below 32°F (0°C). For ex­ ample, a day having a mean temperature of 27°F (-3°C) would equal five freezing degree-days. Many limnological and meteorological factors effect ice formation and growth. However, certain relation­ ships have been established between freezing degree-days and ice cover distribution.

Daily mean air temperatures from selected meteorological stations on the Great Lakes were used to determine the accumulations of freezing degree-days. The stations were Duluth, Minnesota;

3 Sault Ste. Marie, Michigan; Green Bay, Wisconsin; Alpena, Michigan; Cleveland, Ohio; and Rochester, New York. Graphs of the accumulated freezing degree-days versus time were plotted for each of the stations (Plates 1 through 5). The curve of the long term mean was superimposed on each of the graphs. This aided in determining relative winter severity, the approximate date of the maximum degree—day accumulation, and the approximate date of maximum ice cover.

Freezing degree-days were tabulated for the period between November and April. Temperatures were obtained from the Weekly Weather and Crop Bulletin issued by the U. S. Department of Commerce, National Weather Service. Reconnaissance flight dates are also indicated on the graphs.

WINTER CHARACTERISTICS

Temperatures for the 1969-70 winter can be generally classified as below normal. This is indicated by the above average accumula­ tion of freezing degree-days for each of the stations. The accumulation during the last half of December was more rapid than normal and led to shipping problems because of early ice formation in the connecting channels.

Temperatures in the Great Lakes area were generally near normal during the first two weeks of November. During the third week a strong cold front stretched across the mid-continent from north to south. It caused cold weather and below normal temperatures in the for the remainder of November. Below normal temperatures persisted through December and were accompanied by other unusual weather. For example, Duluth, Minnesota, recorded 38.8 inches (98.6 cm) of snowfall for December, which was the second greatest in 99 years of record, while to the east, Sault Ste. Marie, Michigan, experienced 110.6 hours of sunshine, the sunniest December on record. On Lake Ontario to the south, Rochester, New York, had its heaviest monthly snowfall in 86 years (42 inches - 107 cm) and Syracuse, New York, recorded 52 inches 132 cm), the greatest in 67 years.

Low temperatures, continued into January from December and set new records for duration of temperatures below the freezing mark. Houghton Lake, Michigan, had a total of 47 days with temperatures of 32°F (0°C) or below. New Arctic outbreaks during the third week of January brought temperatures 12° to 16°F below normal around the lake perimeter and as much as 22°F below normal at interior sites.

The week ending January 25 found Duluth, recording temperatures 14°F below the normal of 9°F (-13°C); Cleveland, 16°F below the^ normal of 28°F (-2°C); and Flint, Michigan, in the interior, 22°F

4 below the normal of 22°F (-6°F). Temperatures for the month of February were generally below normal due to repeated outbreaks of Arctic air. The month was notable for its lack of precipitation. Alpena recorded only 0.27 inches (0.69 cm), the driest in 98 years, while to the west, Milwaukee accumulated only 0.13 inches (0.33 cm), the second driest since 1877. The monthly March temperatures across the basin varied from normal to slightly below normal. March was the eleventh consecutive month with temperatures below normal at Erie, Pennsylvania. By the end of the second week in April, all stations in the Great Lakes area were reporting weekly temperatures above freezing, signaling the end of the ice forming season.

DATA PRESENTATION

Ice Charts

Thirty-three ice charts were prepared from data obtained on 14 visual aerial reconnaissance flights. These included eight regularly scheduled flights, two supplementary helicopter flights, and four flights made by the Coast Guard for operational purposes. The ice charts show symbolically the principal characteristics of the ice including boundaries, concentrations, ages, types, topo­ graphy, and limits of observed areas (Table 1). With the exception of Lake Ontario which is covered by the Canadian Department of Transport, ice charts were prepared for each of the Great Lakes including Lake St. Clair. Supplementary ice charts are shown for Whitefish Bay, the St. Marys River, and the Straits of Mackinac. The supplementary charts portray the ice cover of those areas in greater detail.

Ice Summary Charts

Two Ice Summary Charts showing all of the lakes were prepared from information obtained from Lake Survey Center ice reconnaissance flights, ice record cards (shore observations), Canada Department of Transport ice charts, and U. S. Coast Guard ice messages. Plate 6 illustrates conditions during the period February 16 to 18, 1970, showing maximum ice cover patterns on the lower lakes. The period March 10 to 17, 1970, shows maximum ice cover on the upper lakes but less than maximum cover on the lower lakes (Plate 7).

DISCUSSION

Lake Superior

Lake Survey Center ice reconnaissance flights over Lake Superior were scheduled for the period of estimated maximum ice cover. U.S. Coast Guard operational flights continued well into the breakup stage. The first scheduled flight took place on March 17, 1970. It covered the St. Marys River and all of the lake except the

5 extreme northeastern portion. The second scheduled flight took place on March 24. Supplementary flights were made over Whitefish Bay and the St. Marys River on February 6, and 25, March 31, and April 1, 3, and 10. The flight on February 6 and all of the April flights were Coast Guard operational flights. These eight flights resulted in the distribution of 17 ice charts: five of Lake Superior, seven of Whitefish Bay, and five of the St. Marys River (Plates 8 through 24). The dates of the four Lake Survey Center reconnaissance flights are indicated on the freezing degree-day graphs for Duluth and Sault Ste. Marie (Plate 1).

Ice on Lake Superior was first reported in the harbor of Grand Marais, Minnesota, on December 2, 1969. On December 7 ice was reported in Duluth-Superior Harbor. By December 15 Ashland harbor, Wisconsin, contained a 7-tenths concentration of drifting ice. However, it was not until the middle of January that any appreciable amounts of ice cover formed on the lake. On January 31, 1970, solid ice was reported in the harbors around the lake, with exten­ sive shore ice formation all along the south shore. Ice in the St. Marys River hindered late running ore carriers, and the last ship was passed down through the on January 11, ending the longest shipping season ever recorded on the upper lakes.

The freezing degree-day accumulations at both Duluth and Sault Ste. Marie were well above normal by the end of January. Above average accumulations continued through February into March. The low temperatures during this two-month period were ideal for ice formation. At the time of the first flight (March 17, 1970) the lake was estimated to be 80 percent ice covered. The composition of the ice cover was varied, and concentrations ranged from 2-tenths of young ice brash to 10-tenths of winter ice. Winter ice was located in Whitefish Bay, along the south lake shore west to Marquette, and in Keweenaw Bay. Off shore north of Grand Island (Munising, Michigan), extensive areas of mixed young and winter ice at 10-tenths concentration were observed. The immediate Duluth and Apostle Islands area, and Thunder, Black, and Nipigon Bays along the north shore all contained heavy winter ice. Much of the remaining lake area contained 7 to 9-tenths concentrations of young and winter ice. This ice was composed mostly of brash, cake, and small to medium size floes, carrying a light to heavy snow cover. At the time of the first flight, the northern half of the lake generally contained young ice while the southern half contained winter ice, indicating a southerly movement of the cover. The ice sheet along the south shore, from Keweenaw Point to Ashland, contained numerous leads which were oriented normal to the shore line. This unusual pattern of leads indicated a general eastward movement of the ice cover. Three large areas of open water were located along the north shore. One was along the southeastern shore of Isle Royale, and another at the entrance to , extending westward to the vicinity of Grand Portage. The third area began

6 just west of Grand Marais, Minnesota, and extended southwesterly to within a few miles of Duluth-Superior Harbor. This was the first time that so large an open water area had been observed in this end of the lake.

The second flight over Lake Superior took place on March 24, 1970. At that time the lake was estimated to be 85 percent ice covered. The freezing degree-day accumulations reached their peak shortly after March 24, and the maximum ice cover was assumed to have occurred about that time. The extensive open water area at the western end of the lake had increased in size to cover the area north of a line between Grand Portage, the Apostle Islands, and Duluth. One other large open water area was located just south of Keweenaw Point. The areas totally covered by winter ice had increased in the southeastern portion of the lake and were generally located southeast of a line running from Cape Gargantua on the Canadian shore to Stannard Rock, then to the vicinity of Marquette. The 7 to 9-tenths concentration of floes along the Keweenaw Peninsula had consolidated to form a 10-tenths concentra­ tion of ice extending out to mid-lake in some areas. The remaining areas of the lake were covered by a mixture of young and winter ice in the form of drifting brash, cake, and floes, ranging in concentra­ tion from 6 to 9-tenths. In Whitefish Bay, at the eastern end of the lake, the winter ice appeared to be more consolidated, and con­ tained numerous ridges and windrows, to the west of Isle Parisienne. The entire ice surface contained a snow cover that varied from light, to heavy and drifted. A very prominent crack ran from south to the vicinity of Naomikong Point. A large open water area was located at the entrance to the St. Marys River near Birch Point.

Three subsequent operational flights were made by the Coast Guard on April 1, 3, and 10. The ice distribution patterns reported from these flights showed progressive deterioration of the ice cover.

An upbound vessel passed through the Soo locks on April 1 opening Lake Superior to navigation, thus making the winter lay up the shortest in Great Lakes history—only 75 days. However, ice continued to hinder navigation. Winds and currents concentrated large areas of drift ice in Whitefish Bay, and ships required ice­ breaker assistance as late as April 15. The last ice above the locks was reported at Point Iroquois on April 27, 1970.

Lake Michigan

Five scheduled reconnaissance flights were made over areas of Lake Michigan on February 25, March 10, 17, 24, and 31, 1970. Two additional operational flights were made by the U. S. Coast Guard on February 6 and April 3. Seven ice charts were prepared from the data gathered; six of the northern part of the lake, and one

7 of the lake perimeter (Plates 25 through 31). The dates of the Lake Survey Center flights are shown on the freezing degree-day graph for Green Bay (Plate 2)•

The first report of ice was on November 27, 1969, when the water level gage observer at the south end of Green Bay reported skim ice forming. On December 20, ice was reported forming at the Mackinaw City docks and on December 22 in the harbor of Port Inland. By January 6, 1970, Mackinaw City and Port Inland reported extensive ice. A tanker required Coast Guard assistance to enter St. Joseph harbor because of a reported 3 feet (1 m) of ice at the channel entrance. The Coast Guard flight over northern Lake Michigan on February 6 reported ice extending from Beaver Island through the Straits, to the east end of Bois Blanc Island.

The first scheduled flight over northern Lake Michigan was made on February 25. Green Bay had an almost solid winter ice cover, except for an area between Washington Island and Peninsula Point. The ice cover north of Beaver Island, and through the Straits, had increased and extended south to include Little Traverse Bay and nearly all of .

The flight around the lake's perimeter was made on March 10. During that same week the freezing degree-day graph for Green Bay began to level off indicating near maximum accumulation and the greatest areal extent of ice cover. The lake at that time (March 10) was estimated to be 30 percent ice covered. Heavy winter ice was confined to the northern end of the lake, and various concentra­ tions of drift ice were distributed along the southern shores. Green Bay still contained winter ice but the snow cover had become puddled and refrozen. An area in the northern part of the bay consisted of brash floes at 9-tenths concentration extending to the west from Washington Island then north to Peninsula Point. A 10- tenths concentration of heavy winter ice was observed in the lake northeast of a line running from Point Patterson to Beaver Island to Waugoshance Point. The area also contained a puddled and refrozen snow cover. Winter ice extended southward from lie Aux Galets and covered Little Traverse and Grand Traverse Bays. The area north­ west of Sleeping Bear Point was covered by a 5 to 9-tenths concen­ tration of brash, and small to medium size floes of young ice. The eastern shore, from Ludington to Benton Harbor, contained light concentrations of brash and sludge. The mid-lake area of the southern basin contained an extensive area of brash and cake at 5- tenths concentration. The western shore from the vicinity of Port Washington, north, contained a narrow band of brash and sludge ice of 5-tenths concentration.

The slope of the degree-day graph for Green Bay began a down­ ward trend shortly after the March 10 flight. The data from later Coast Guard reports and reconnaissance flights indicated a general

8 deterioration of the ice cover. A Coast Guard operational flight on April 3 reported ice in the immediate Straits area and in the lake north of Beaver Island. Little Traverse Bay was reported to contain an 8-tenths concentration of drifting floes, while Grand Traverse Bay had a heavy concentration of winter ice with numerous cracks aligned in an east-west direction.

The last report of ice was on April 18. Low concentrations of rotten ice were reported in the vicinity of White Shoal and Grays Reef.

Lake Huron

Ice reconnaissance flights over portions of Lake Huron took place on February 25, March 11, 17, 24 and 31, 1970. The Coast Guard made an early season operational flight over the Straits area on February 6, and reported drift ice in the lake as far south as Rogers City. The reconnaissance flight of March 11 covered the entire U.S. side of the lake and a small portion of the Canadian side. A supplementary helicopter flight was made over the southern end of the lake including on March 17. Two Lake Huron ice charts were prepared from data obtained on the March 11 and 17 flights (Plates 32 and 33).

Lakeport, near the southern end of the lake, reported skim ice forming on November 3, 1969—one of the earliest reports of ice for that part of the lake. Harbor Beach reported ice forming on December 17, and Harrisville reported ice on December 24. Ice was not reported in the Straits of Mackinac until January 6, 1970.

The freezing degree-day accumulations at Alpena were greater than normal for the months of December 1969, and January and February 1970, indicating good ice forming conditions. The first scheduled reconnaissance flight took place on March 11, 1970. From observations made on this flight, the lake was estimated to be 50 percent ice covered. An extensive ice sheet was observed over the entire lake, except in the central basin. The Straits of Mackinac and the contained a 10-tenths concentra­ tion of heavy winter ice with a medium to heavy snow cover. Saginaw Bay contained a solid, snow covered ice sheet that extended out to Charity Island. The southern basin of the lake contained a mixture of young and winter ice of 10-tenths concentration, extending north from Port Huron to the vicinity of Harbor Beach on the American side, and to near Kincardine on the Canadian side. The solid cover was bordered by various concentrations of drift and brash ice at 2 to 9-tenths concentration extending out to the central basin. A prominent lead was observed parallel to shore in the southern portion of the lake extending from Port Austin southward to Port Huron.

9 The slope of the degree-day curve for Alpena leveled off after March 11, 1970. On March 17, a supplementary helicopter flight was made over the southern end of the lake and Saginaw Bay. Ice concentrations had decreased to 3-tenths in the Port Huron area, and the ice was composed mostly of brash and cake. The shore lead observed on the previous flight had enlarged and was bordered by a large area of brash at 5-tenths concentration. Saginaw Bay contained a large open water area at the mouth of the Saginaw River. The bay ice generally contained a puddled snow cover. The reduction in the concentration of ice cover in the southern portion of the lake and the flattening of the degree-day curve for Alpena signaled a moderation of ice-forming conditions. The examination of these data indicate that the maximum areal extent of ice cover occurred between March 11 and 17. The degree- day curve began its downward trend during the week ending April 5, signaling an end to ice formation on Lake Huron.

The dates of last ice varied considerably on Lake Huron, mainly due to the southerly movement of drift ice. Harrisville reported last ice on April 4, Harbor Beach on April 8, and Lakeport on April 11. Ice was still reported in the Straits area on April 17.

Lake St. Clair

A total of four observation flights were made over the lake and four ice charts were prepared from these data (Plates 34 through 37) . The scheduled flights took place on February 17, March 5, and 11, 1970. A supplementary helicopter flight was made over the area on March 17.

The first report of ice was from the St. Clair flats area on December 3, 1969, almost a week earlier than during the 1968-69 ice season. The last half of December was extremely cold, and large areas of the lake were reported ice covered. By January 1, 1970, Anchor Bay was more than half covered by ice. The St. Clair Shores area contained extensive fields of consolidated brash and cake. Ice 6 to 9 inches (15 to 23 cm) thick was reported in the protected bays north of the Clinton River.

The relatively early ice cover on Lake St. Clair created navigation problems in the lower St. Clair River. Because of the ice cover on the lake, drift ice in the river could not be passed downstream. Consequently, massive ice jams formed in the lower river near Algonac. The jams trapped a number of vessels which required Coast Guard assistance.

During January and the first half of February, persistent cold weather caused the lake ice to increase in thickness and areal extent. On February 17, the lake was estimated to be 95

10 percent covered. For the most part the cover was composed of winter ice with a topping of light drifted snow. An extensive area of medium to large floes was located near Windmill Point. These floes were of 7-tenths concentration and were made up mostly of young ice. A prominent crack extended from near Strawberry Island to the vicinity of Gaukler Point. A number of small open water areas were scattered about the various channel mouths in the St. Clair flats.

The last half of February and the first week of March had a number of days with temperatures in the low forties (°F - about 5°C). These relatively high temperatures, combined with wind and bright sunshine, had an adverse effect on the ice cover, and from data obtained on the second flight (March 5) the lake was estimated to be 90 percent ice covered. Large open water areas appeared in Anchor Bay and along the western shore from the Clinton River to the St. Clair Shores area. Extensive open water was also located between Gaukler and Windmill Points extending 2 to 3 miles (3 to 5 km) out into the lake.

The last scheduled flight took place on March 11, and the lake was estimated to be 85 percent ice covered at that time. The ice cover had been slowly deteriorating since the first flight on February 17. Winter ice of 10-tenths concentration was located in the southeast quarter of the lake and around the perimeter of Anchor Bay. The western half contained winter ice of 9-tenths concentra­ tion made up of brash, cake and small to medium size floes, and a puddled snow cover. Two extensive open water areas were located in the western portion of the lake. One was in the central area of Anchor Bay, and the other was in the Gaukler Point-Bell River- Windmill Point area.

The last report of ice came from the Coast Guard station at St. Clair Shores on March 24, 1970.

Lake Erie

Three reconnaissance flights were made over Lake Erie: February 17, February 24 (a supplementary helicopter flight), and March 5, 1970. Three ice charts were prepared from the data collected (Plates 38, 39 and 40). Flight dates are also indicated on the freezing degree-day graph for Cleveland (Plate 4).

First ice was reported at the Fermi water level gage, at the western end of the lake, on December 4, 1969. The Coast Guard also reported ice in the outer channel of Toledo Harbor on this date. Shore ice was reported in on December 8, and on December 23 extensive ice was reported at Marblehead. This early ice cover in the western basin created problems for shipping. On December 24, two vessels required Coast Guard assistance.

11 The accumulation of freezing degree-days was greater than normal at Cleveland, Ohio, for December and early January. By January 14, 1970, a number of areas were reporting heavy ice con­ centrations that extended over the length of the lake from Toledo in the west to Sturgeon Point in the east. Freezing degree-days continued above average through January and into mid-February, even though the daily temperatures during the fourth week of January were consistently above freezing. The reports of ice in early December and the greater than normal degree-day accumulations of December and January were indicators of an early lake-wide ice cover.

On February 17, 1970, the lake was estimated to be 95 percent ice covered. Most of the lake surface contained a 10-tenths con­ centration of heavy winter ice which carried a heavy, drifted snow cover. Winter ice covered the entire western basin and nearly all of the lake east of a line running from Cleveland to Pte. Aux Pins. The remaining area, extending from Cleveland to Pelee Island, was covered with young and winter ice of 9-tenths concentration com­ posed of small, medium, and large floes, with some scattered brash. Numerous large leads began just east of the island area and followed the south shore to the vicinity of Erie, Pennsylvania. The ice in the eastern end of the lake, from Erie to Buffalo, contained many ridges, rafted, and jammed areas.

The degree-day curve leveled off after February 17, and data from a supplementary helicopter flight on February 24 indicated the lake to be approximately 70 percent ice covered. The area of great­ est change was in the central basin between Pelee Island and Ashtabula, Ohio. Extensive open water areas were located east of the islands, and the remaining central basin area contained winter ice ranging in concentration from 1 to 7-tenths. The western and eastern ends of the lake maintained their cover of winter ice at 10-tenths concentration, but the snow cover had melted and become puddled.

Air temperatures moderated somewhat during the last week of February and the first week of March, as indicated by the downward slope of the degree-day curve for this period (Plate 4). The moderate temperatures affected the ice cover by causing it to break up and form new distribution patterns. On March 5 the lake was again estimated to be 70 percent ice covered. The 10—tenths con­ centrations of winter ice were confined to the island area in the west and to the eastern basin which also contained large leads extending from Erie to Sturgeon Point, then northward to Point Abino and westward to the vicinity of Port Dover. The central basin between Erie, Pennsylvania, and Pelee Island, contained brash, cake and floes varying from 2 to 10-tenths concentration. The remaining snow cover was melted and puddled. The north shore of the lake contained a 3 to 10 mile (5 to 16 km) wide band of open water

12 extending from the eastward to the Long Point area. This same open water area spread to the south from Pelee Point and then eastward along the south shore to Ashtabula.

During the week ending March 15, the freezing degree-day curve for Cleveland began its downward slope indicating the end of the ice formation period. By March 24 much of the ice cover had disin­ tegrated, leaving many areas ice free. The western basin was clear except for some shore ice in the island area. Sandusky Bay contained rotten ice, but the lake off the bay entrance was clear. Areas of rotten ice ranging from 4 to 9-tenths concentration were located along the southern shore from Cleveland to Buffalo. This breakup exhibited the chracteristic ice distribution pattern for Lake Erie; drift ice concentrating along the southern and eastern shores.

The last report of ice was on April 27 from the Buffalo area and on April 29 from the Black Rock Canal area of the .

Lake Ontario

Ice information for Lake Ontario was obtained from Canadian ice charts, U. S. Coast Guard ice messages, and Lake Survey Center water level gage observers.

First ice was reported in the Tibbetts Point area at the entrance to the St. Lawrence River on December 23 and in the Rochester area on December 24, 1969. The first report of ice from the western end of the lake came from the gage observer at Olcott on January 1, 1970. This first ice was composed mostly of drifting brash and cake, with some shore ice accumulations.

The freezing degree-day curve for Rochester (Plate 5) reached its maximum during the week ending March 15, which is about normal for the lake. During this period the lake contained an estimated 15 to 20 percent ice cover. In the eastern end and the approaches to the St. Lawrence River, the ice followed normal patterns of accumulation.

The last report of ice came from the Tibbetts Point area on March 31, 1970.

ACKNOWLEDGEMENTS

This report presents information, in the form of ice charts, obtained from aerial ice observations made during the winter of 1969-70. The program was carried out as a part of the activities of the Ice and Snow Branch of the Great Lakes Research Center, U. S. Lake Survey, U. S. Army Corps of Engineers and was under the general direction of Dr. L. Bajorunas, Director, Great Lakes Research Center. Lake Survey personnel serving as ice observers were

13 R. N. Kelley, B. P. Cavan, and D. A. Prins. Flight support was provided by the Ninth U. S. Coast Guard District (U. S. C. G. Air Station, Traverse City, Michigan and Detroit, Michigan). A general coordination of flight schedules was maintained with the Canadian Department of Transport.

Reorganization Plan No. 4 of 1970 has been put into effect and and the U. S. Lake Survey is now a part of the National Oceanic and Atmospheric Administration (NOAA), Department of Commerce.

14 TABLE 1 ICE CHART SYMBOLS

TOTAL CONCENTRATION BOUNDARIES

Open Water Observed

Assummed 0\\\ 1-3 Tenths Coverage (Very Open Pack) Undercast 4-6 Tenths Coverage (Limits) (Open Pack) Limit of 7-9 Tenths Coverage observed (Close Pack) area

10 Tenths Coverage (Consol Pack)

AGE AND SIZE OF FLOES

Station Model

A Cn C DOM, SEC n1n2n^ NEW

A - IND for Cn AGE OPENINGS IN ICE DOM - lOths DOM AGE SEC - lOths SEC AGE VrV+H CRACK AGE - Y (Yng) - Young Ice (CRK) W - Winter Ice MW - Medium Winter LEAD TW - Thick Winter POOL or Cn - Total CONC of n.n and POLYNYA n~ in lOths (PLYA) n - CONC of brash and ^ cakes in lOths Relative n2 - CONC of small and movement medium floes in lOths between n_ - CONC of large floes and two floes ice fields in lOths

C - CONC of NEW ice in lOths NEW - SLH - Slush IR - Ice Rind SLG - Sludge PCK - Pancake TABLE 1 (CONTINUED)

TOPOGRAPHY

STAGE OF MELTING T COND Station Model T - Type of pressure ice Pd AAA - Rafted n, COND /W\ - Ridged Pd - IND for Melting n - lOths of area Q Q Q - iiummocked COND - TH - Thaw Hole R - Rotten Ice Rfzn - Refrozen COND - I. - Light H - Heavy NOTE: No COND means MOD.

SNOW COVER ABBREVIATIONS Station Model AMT - Amount Sn BSH - Brash AMT, COND CKE - Cake CONC - Concentration COND - Condition Sn - IND for Snow CONSOL - Consolidated AMT - 0 - No Snow DOM - Dominant L - Light H - Heavy IND - Indicator NOTE: No AMT means MOD MOD - Moderate COND - D - Drifted SEC - Secondary Cr - Crusted SLG - Sludge Pd - Puddle RFZN - Refrozen APR

MAR

FED

JAN

DEC

NOV

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DEC

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PLATE 2 APR

MAR

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JAN

DEC

NOV

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STATUTE KILOMETERS

0

7 0 — 4

SM

1970 N o.

MAR

24 0900-1605

Reconnaissance Date Time

o CD J 00

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43 -43

Port Huron

LAKE ST. CLAIR ICE CHART

KILOMETERS

5 0 5 STATUTE MILES

Reconnaissance No. STC-l-70 Date 17 FEB 1970 Time 1030 - 1500

M t. Clemens

W LD

Windsor

83

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