U.S. DEPARTMENT OF COMMERCE

Frederick B. Dent, Secretory

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

Robert M. While, Administrator

ENVIRONMENTAL RESEARCH LABORATORIES

Wilmot N. Hess, Director

NOAA TECHNICAL REPORT ERL 325-GLERL 1

(GLERL Contribution No. 20)

Great Lakes Ice Cover, Wil1ter 1913-14

R.A.ASSEL

BOULDER. COLO..

July 1974

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington. O. C. 20402
ENVIRONMENTAL RESEARCH LABORATORIES

TIle: mission of the Environm-entat Ruse:arch LibofatQrics is to itudy the oua.ns. inl<lnd waters. the lower

and upper atmosphere, the space covironmenl, ilnd the ciTth, in search of the underStanding needed to provide more useful services in improving man's prospe<:u for survival as inf1uenc~ by th~ physical environment.

labofatories conuibuling to these studies are:

Atlantic Oceanographic and M~te()rologk()1 Lobororor;('s (AOML): Geology .and geophysics of occan basins

and borders, oceanic process,e$, sea·air interactions and remou: sensing of ocun prousses and characteristics

(Mi.mi, florid.).

Pucifk Mari~ Environmental Loborotory (PM£L): Environmental pto,esw:s with emphasis on monitoring

ilnd predicting the effects of man's activities on estuarine, COJsut• .lnd ne~(-shore mJrine processes (Seatde,

W>SIlingtonI.

Grt'ilt Lakes Environmental R~seor,h Laborotory rGL ERL): Physiul, chemical, ~nd biological. limnology, take~air interactions,lake hydrology,lake level forec~tinl, .and l~ke ice studies (Ann Arbor, Michigan).

Atmosph¥rJc Physics lInd Chemistry Laboratory (APCL): Prousses of cloud and precipUtion physia;

chemical composition and nude~tin& subsunus in the lower almosphere; and bbor.atory and field experiments

toward developing fe.uible methods of \n.ther modifiGation.

Air Resources Laboratories (ARL); Diffusion, tT.ansport, and dissipation of atmospheric conuminants;

de.elopment of methods for prediction and GOfttfoi of atmospfte-ric pollution; leophysical monitoring for

<lIm.!i< m.nge ISilver Spring, M.ryl.ndl.

Gtophys/Ctl/ Fluid Dynamics Laboratory (GFOL): Dynamics and physics of eeophysicaf fluid systems;

development of .I theored"' basis, through mathematical moddine and computer simulation, for the behilvlor

and properties of the atmosphere and the oceans (Princeton, New Jersey).

Ntll;OfMI S.wt'~ Storms LabofQtory (NSSL): TorQdoes, squiUl Una, thunderstorms, ~d other severe local

convective p1w:nomen.a directed toward improwd methods of prediction Ind detection (Norman~ Oklahoma).

Sp«~ El1vironm~nt LobortJtOf)l (SEL): Sollr~tertc!strill physics, service and technique development in the areas of environmental menitonn. and forecutlng. . •

An-anomy LfIborqtory (AL).- Theoretical. laboratory, rCKket, ;and s;tcUitt studies of the physica' and:

chemical proc~ controlUng the Ionosphere .nd eXO$phere of the earth and other plaMts, and of the

dynamics of their interactions with hi,h.-altitude meteorology.

Wave' Propagation Laboratory (WI'L): Development of new methods for remote sensing of the geophysical

erwironment with 'Pec~1 emphasis on optiul, microwave and acoustic sensing systems.

Mt1rin~ EcoSystem AntJlyJls I'rogrtJm Office (MESA): PSans and directs interdisciplinary analyses of the

physical. chemic.I, geological. and bioloaical characteristics of selected coastal regions to assess the potential

effects of O(Qn dumping~ munici~landindustrial waste discharges, oil pollution, or other activity which m.Jy

have environmental imput.

Weather Modiflcotion Program OffJu (WMPO): Plans .and directs ERL 'Neither modification research

ictivlties in pn~cipitation enhancement and severe storms mitigat.on and operates ERl's reseuch aircraft.

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

BOULDER, COLORADO 80302
DISCLAIMER

The NOAA Environmental Research Laboratories do not approve,

recommend. or endorse any proprietary product or proprietary

material mentioned in this publication. No reference s1ulll

be made to the NOAA Environmental Research Labot:atories, or

to this publication furnished by the NOAA Environmental

Research Laboratories, in any advertising or sales promotion

which would indicate or illlply that the NOAA Emrironmental

Research Laboratories approve, recommend. or endorse any

proprietary product or proprietary material mentioned herein,

or which has as its purpose an intent to cause directly or

indirectly the advertised product to be use~ or purchased

because of this NOAA Environmental Research Laboratories

publication.

ii
CONTENTS

ABSTRACT

1. INTRODUCTION

2. DATA COLLECTION

3. DATA PRESENTATION

3.1 Freezing Degree-Days

3.2 Composite Ice Charts

3.3 Ice Charts

4. DISCUSSION

4.1 Winter Characteristics

4.2 General Seasonal Trends in Ice-Cover Distribution

4.3 Lake Superior

4.4 St. Marys River

4.5 Lake Michigan

4.6 Lake Huron

4.7 St. Clair River and Lake St. Clair

4.8 Lake Erie

4.9 Lake Ontario

5. ACK.NOWLEDGMENTS

6. APPENDIX

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13

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A.I.

A.2.

A.3.

A.4.

A.5.

A.6.

A.7.

A.8.

A.9.

A.IO.

A.H.

A.12.

A.l3.

A.14.

A.15.

A.16.

A.H.

A.18.

A.19.

A;20.

A.21.

A.22.

A.23.

A.24.

A.25.

A.26.

A.27.

A.28.

A.29.

A.30.

A.3I.

A.32.

A.33.

A.34.

A.35.

A.36.

A.37.

A.38.

A.39.

FIGURES

Accumulated freezing degree-days - Lake Superior at

Sault Ste. Marie, Mi~h., and Duluth, Minn.

Accumulated freezing degree-days - Lake Michigan at

Green Bay and Milwaukee, Wis.

Accumulated freezing degree-days - Lake Huron at

Alpena, Mich.

Accumulated freezing degree-days - Lakes Erie and

St. Clair at Cleveland, Ohio, and Detroit, Mich.

Accumulated freezing degree-days - Lake Ontario at

Rochester, N. Y.

Composite ice chart - week ending December 16, 1973.

Composite ice chart - week ending December 23, 1973.

Composite ice chart - week ending December 30, 1973.

Composite ice chart - week ending January 6, 1974.

Composite ice chart - weekending January 13, 1974.

Composite ice chart - week ending January 20, 1974.

Composite ice chart - week ending January 27, 1974.

Composite ice chart - week ending February 3, 1974.

Composite ice chart - week ending February 10, 1974.

Composite ice chart - week ending February 17, 1974.

Composite ice chart - week ending February 24, 1974.

Composite ice chart - week ending March 3, 1974.

Composite ice chart - week ending March 10, .],974.

Composite ice chart - week ending March 17, 1974.

Composite ice chart - week ending March 24, 1974.

Composite ice chart - week ending March 31, 1974.

Composite ice chart - week ending April 7, 1974.

Composite ice chart - week ending April 14, 1974.

Composite ice chart - week ending April 21, 1974.

Composite ice chart - week ending April 28, 1974.

Lake Superior ice chart - March 4, 1974.

Whitefish Bay ice chart - March 4, 1974.

St. Marys River ice chart - December 17, 1973.

St. Marys River ice chart - March 4, 1974.

Lake Michigan ice chart - February 27, 1974.

Lake Michigan ice chart - March 4, 1974.

Lake Huron ice chart - February 25, 1974.

Lake Huron ice chart - February 27, 1974.

Lake Huron ice chart - March 4, 1974.

Lake St. Clair ice chart - February 5, 1974.

Lake St. Clair ice chart - February 25, 1974.

Lake Erie ice chart - February 25, 1974.

Lake Ontario ice chart - February 15, 1974.

NOAA-2 VHRR visible image - February 20, 1974.

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TABLES

1. Ice reconnaissance flights - winter 1973-74

2. Key to ice chart symbols

v

Page

3

5
GREAT LAKES ICE COVER, WINTER 1973-74

R. A. Assel

ABSTRACT

Twenty composite ice charts were produced from icecover data received at the Lake Survey Centerl during the

past winter. These charts illustrate estimated ice concentrations and distributions on the Great Lakes at weekly

intervals from mid-December 1973 to the end of April 1974.

In addition, 13 ice charts compiled from data collected by

Lake Survey Center ice observers portray synoptic ice conditions on individual lakes and rivers.

Freezing degree-day accumulations-indicate the 1973-

74 winter was near normal over the Great Lakes. Accumulations were near their seasonal maximum the end of February on southern portions of the Great Lakes and the end

of March on northern portions.

Extensive ice formation in protected shore areas and

shallow parts of the Great Lakes was initiated by below

normal temperatures the second half of December and first

half of January. Above normal temperatures the second

half of January retarded ice formation and caused significant loss of ice in some areas. Ice covers reached their

maximum extent in February and were estimated to extend

over 70 percent of Lake Superior, 20 percent of Lake Michigan, 65 percent of Lake Ruron, 95 percent of Lake Erie,

and 25 percent of Lake Ontario. Mild temperatures in early

March resulted in rapid loss of ice on southern portions

of the Great Lakes so that, by mid-March, they were virtually ice free. By mid-April, the bulk of the ice cover was

gone-on the northern portions of the Great Lakes as well.

The only areas with extensive ice in mid-April were the

west end of Lake Superior, various Lake Superior bays, and

the North Channel in Lake Huron. Last reports of ice were

made in late April.

lIn April 1974, the Limnology Division, Lake Survey Center, National

Ocean Survey, was transferred to the Great Lakes Environmental

Research Laboratory of the Environmental Research Laboratories.

Several references to the Lake Survey Center appear since the work

was being conducted under that organization at the time.
1. INTRODUCTION

The Great Lakes Environmental Research Laboratory has an ongoing

project for the investigation of lake ice-cover distribution. Reports

describing work carried out under this project for past winters, beginning with the 1962-63 winter season, are available from the Lake Survey

Center, Detroit, Mich. In this report, data collected during the 1973-

74 winter are described. As in previous reports in'this series, this

report contains a description of ice-cover fo~tion, growth, und dec~y

based on data collected the past winter. A brief sUllldlary of winter

t~mperatures is also incluced.

2. DATA COLLECTION

Ice charts, satellite imagery, and surface ice reports made up the

bulk of the ice-cover information collected. Ice charts were received

from the Ice Navigation Center, Cleveland, Ohio, and Ice Forecasting

Central, Ottawa, Canada, throughout the winter. Lake Survey Center

personnel also produced ice charts from data collected on visual aerial

ice reconnaissance flights. The primary information on ice charts is

ice concentration. ice distribution, and age and size of ice floes.

Surface reports of ice thickness and ice conditions were received from

Lake Survey Center and U.S. Coast Guard ice observers. NOAA-2 VHRR

satellite imagery was received from the National Environmental Satellite

Service in Washington. D.C•• from November 1973 through April 1974.

Lake Survey Center personnel completed 12 aerial ice reconnaissance

flights between December 17. 1973, and March 21. 1974. Approximately

37 hours and 3660 miles (5860 km) were logged on tpese flights. the

majority of which used chartered Cessna 172 and Cessna 182 aircraft.

Three flights were made aboard U.S. Coast Guard aircraft during ice

patrol flights. Flight dates and areas covered are given in table 1.

Data collected on aerial ice reconnaissance flights included observations of ice concentrations, ice distributions, ice floe size, ice

age, and surface characteristics. This information was plotted on worksheets and redrafted on small-scale ice charts, which were sent to the

Ice Navigation Center in Cleveland after each flight. Aerial photography of ice cover was also made on most flights over the St. Marys and

St. Clair Rivers in support of the Demonstration Program to extend the

naVigation season. Four visual aerial ice reconnaissance flights were

made to coincide with the time of estimated maximum ice cover on the

Great Lakes as part of the ongoing lake ice-cover distribution project.

3. DATA PRESENTATION

3.1 Freezing Degree-Days

As in past winters, freezing degree-day accumulations, based on

average weekly temperatures, were maintained for selected National

Weather ,Service meteorological stations on the perimeter of the Great

2
Table 1. Ice Reconnaissance PZights - r-linter 1973-74

Flight No. Date Area

1 Dec. 17 St. Marys River

2 Jan. 8 St. Marys River

3 Jan. 17 St. Clair River, !..ake St. Clair

4 Jan. 24 St. Marys Riv~r

5 Feb. 5 St. Clair River, Lake St. Clair

6 Feb. 15 Lake Ontario

7 Feb. 25 (CG) Lake Erie

8 Feb. 25 St. Clai~ River, Lake St. Clair,

Southern Lake Huron

9 Feb. 26 St. Marys River

10 Feb. 27 (CG) Northern Lakes Michigan and

Huron

11 Mar. 4 (CG) Northern Lakes Michigan and

!luron, Lake Superior, and

St. Marys River

12 Mar. 21 St. Marys River

(CG) = Coast Guard Flight Support

3
Lakes: Duluth, Minn.; Sault Ste. Marie, Mich.; Alpena, Mich.; Green

Bay, Wis.; Milwaukee, Wis.; Detroit, Mich.; Cleveland, Ohio; and Rochester, N. Y. Freezing degree-days measure the cumulative temperature

departure from 32°F (O°C). One freezing degree-day is accumulated

when ~he mean daily temperature is 31°F. The mean daily temperature

is defined as the mean of the daily maximum and minimum temperatures.

Thus, for a mean daily temperature of 2SoF, 7 freezing degree-days are

accumulated. Graphs of freezing degree-days are given for each of the

Great Lakes (fig. A.l through A.S). The graphs show 1973-74 accumulations and a IO-year mean.

3.2 Composite Ice Charts

Twenty composite ice charts (fig. A.6 through A.25) illustrate the

seasonal pattern of ice formation, growth, and decay on the Great Lakes

from Decemher 16, 1973, to April 28, 1974. These charts portray

estimated ice conditions at weekly intervals, based on a subjective

evaluation of available ice-caver information. Ice charts compiled

by the Lake Survey Center, U.S. Coast Guard Ice Navigation Center. and

Canadian Ice Forecasting Central provide the bulk of the ice-caver information used to compile composite charts. NOAA-2 VHRR satellite imagery

was used to supplement these data.

Freezing degree-day accumulations at the eight locations noted

earlier also are given on the composite ice charts. Weekly, seasonal.

and normal seasonal accUlllulations are given to indicate the severity

of each week and the relative severity of the seasonal accumulations.

3.3 Ice Charts

Thirteen ice charts. figures A.26 through A.38. compiled by the

Lake Survey Center, illustrate synoptic ice conditions and provide

greater detail than composite ice charts. Table 2 is a key to symbols

and abbreviations used on these charts. Data for eight of the ice

charts were collected on flights near the time when it was estimated

the lakes would have their greatest ice caver. The remaining five ice

charts were made during flights over the St. Clair and St. Marys Rivers

in connection with the Lake Survey Center's participation in the Great

Lakes-St. La~nce Seaway Navigation Season Extension Demonstration

Program.

4. DISCUSSION

4.1 Winter Characteristics

Two values of freeZing degree-day accumulation can be used to

characterize a winter season: (1) maximum accumulation and (2) date

of maximum accumulation. The first value gives a measure of winter

severity; and the second value, that is, the "date, marks an inflection

4
TOTAL COIICENTRATION

TabLe 2. Key to Ice Chart SymboLs

OPENINGS IN ICE BOUNDARY

[illi -:.::.: OPEN WATER

/' CRACK OR BROKEN OBSERVED

TRACK VISUALLY § 1-3 TENTHS COVERAGE

(VERY OPEN PACK) :::- LEAD ---- ASSUMED

rrrn 4-6 TENTHS COVERAGE

(OPEN PACK) (fJ) POOL

(PLYA)

OR POLYNYA ~UNDERCAST (LIMITS) 7-9 TENTHS COVERAGE

(CLOSE PACK)

llELATIVE MOVEMEII ..._-- LIMIT OF f§§ 10 TENTHS COVERAGE BETWEEN TWO FLO OBSERVED DATA (CONSOL PACK)

AGE AND SIZE OF FLOES

Station Model

• Cn

ACTUAL AGE (Ul) (n2) (n3)

A -IND !OR ACTUAL AGE

ACTUAL AGE

SS -1lllW ICE 2" or less

THIN -THIN ICE 2-6"

KED -KEDIUM ICE 6-12-

TIlK -THICK ICE 12-30"

V'1'lIX -VERY THICK 30" or)

Cn - Total C(JI(C of nlu2 and

03 in lOths

nl - CONC of brash and

cakes in 10ths

u2 - CONC of small and

medium floes in IOths

n3 - COlIC of big floes and

ice fields in 10ths

....!!....

\0

SMa.! COVEll.

Station lloJel

(n)

s" IND for Snow

" (n) - Tenths on lee

7ii1--------

STAGE OF MELTING

Station !Ioclel

Pd

(n)+(n)'1B+(n)F

Pd - IND for Helting

(n) - Tenths on Ice

(n)TH - Tenths Thaw Holes

(n)F - Tenths Frozen

TOPOGRAPHY ABBllEVIATIOIIS

- RAFTED BSH • Brash

(n)

CK - Cake

IVV\ - RIDGED

(n) NOT OBS - Not Observed

no HllMMOCKED SLG • Sludge

(n)

RFZN = Refrozen

(n) - NUMllER OF TENTHS

5
point separating a period of generally increasing ice formation potential from a period of decreasing ice formation potential. Using Rondy's2

classification of winter severity, which is based on maximum freezing

degree-day accumulations, the 1973-74 winter was in general normal.

Dates of maximum freezing degree-day accumulation occurred in late

March and early April on the northern half of the Great Lakes and in

late February on southern portions, with accumulations at Cleveland

occurring in mid-January to prOVide an exception to this trend. Average dates of maximum freezing degree-day accumulation given in the

Great Lakes Ice Atlas indicate that the 1973-74 maximum accumulations

were nearly normal on northern portions of the Great Lakes, that is,

at Duluth, Sault Ste. Marie, Alpena, and Green Bay, while maximum accumulations were 2 to 4 weeks earlier than normal on the southern half of

the Great Lakes, that is, at Milwaukee, Detroit, Cleveland" and Rochester.

4.2 General Seasonal Trends in Ice-Cover Distribution

Ice covers were in general confined to bays, harbors, and shallow

protected areas of the Great Lakes through late January (fig. A.6

through A.12). In February (fig. A.13 through A.16), ice formed over

deeper waters of the lakes and attained its greatest coverage. Mild

spring-like weather the first half of March resulted in.loss of ice

cover 80 that by mid-month the southern half of the Great Lakes was

virtually ice free (fig. 'A.17 through A.19). A cold period' the last

2 weeks of March accounted for some new ice formation. ~spe~ially on

northern lakes (and Lake Superior in particular). as shown in figures

A.20 and A.21. lee covers were well into the decay period by mid-April

(fig. A.22 and A.23), and by the end of Apri~. the only ice of any

significant coverage was located in the west end of. Lake Superior~ in

the three large bays along the north shore of that lake. and in the

North Channel of northeru Lake Buron (fig. A.24 and A.25).

4.3 Lake Superior

Lake Survey Center ice observers made one flight over Lake Superior

on March 4 and produced two ice charts from that flight, figures A.26

and A.27. The iee cycle of Lake Superior. based on available data, is

described below.

Bays and harbors began to freeze over during the second week in

December. By January 20. the southwest end of the lake from Duluth to

Ashland and eastward to esst of Ontonagon had extensive shore ice.

2Rondy, D.R. (1971), Great Lakes Ice Atlas, NOAA Technical Memorandum

NOS LSCR 1, Lake Survey Center, Detroit, lIich.

6
The three bays along the north shore were frozen, with the ice extending

from the mainland to Isle Royale. Whitefish Bay at the east end of the

lake was frozen over. Above normal temperatures the second half of

January slowed the rate of ice formation and caused the loss of some ice

cover. More seasonable temperatures through the first 3 weeks of February resulted in extensive ice formation over the lake. By the week ending February 17, freezing degree-day accumulations were within 75 percent

of their seasonal maximum values, and the lake was estimated to be lO-percent ice cover and near its maximum ice cover for the l~l3-l4 season.

The following ice conditions were observed on an ice reconnsissance

flight over Lake Superior on March 4. Whitefish Bay was completely frozen over, and the south end of the bay had only a little snow on the ice

(see fig. A.27). The lake beyond the bay (fig. A.26) was ice free with

the exception of scattered brash ice. Belts of brash, covering 10 to 20

percent of the area, were observed along the east shore. An open water'

area extending from Whitefish Point to Munising gradually became larger

going west. Shore ice was located south of the open water and brash

ice of various concentrations north of it, while the central part of the

eastern half of the lake was virtually ice free. Going west, brash ice

was once more observed approximately west of a line from Houghton to Marathon. A large pool of open water paralleled the south shore of Isle

Royale and extended eastward from iF, but ice covered 90 t9 100 percent

of the observed area west of Isle Royale; however. observation of the

western half of the lake was severely limited by snow flurries. Rafting

and ridging were evident in portions of the weatern lake ice cover and

cracks and leads. predominstely north-south oriented, were observed

throughout that area. New ice was forming on t~ open water area.

A NOAA-2 satellite image taken February 20 illustrates the general

distribution pattern of ice cover on Lake Superior near the time of

estimated maximum ice cover (fig. A.39).

Mild spring-like weather the first part of March greatly reduced

ice cover on the lake, as shown in figures A.lS and A.19. By March 17.

the eastern half of the lake had only shore ice remaining and the

weatern half had large areas of open water. Low temperatures tbe last

half of March brought extensive new ice formation so that the lake was

once more near maximum ice cover during the second half of March. Mild

temperatures in April brought an end to significant ice formation. By

mid-April, the lake was well into the decay period (fig. A.23). Bays

and harbors were losing ice covers in the third and last week of April.

By the end of the first week in May, all ice reports indicated thet

these areas were virtually ice free.

4.4 St. Marys River

Two ice charts were produced from visual aerial ice reconnaissance

7
flights made over the St. Marys River, one on December 17, 1973, and

the second on March 4, 1974. The following paragraphs describe the

development of ice on the river.

Shore ice was reported forming on the southern end of the river

on December 3 and on the northern part of the river above the locks on

December 11. On the December 17 flight (fig. A.28), the river from

just north of De Tour to Neebish Island and further nort~ along the

east side of Sugar Island contained an almost complete ice cover.

Numerous cracks, leads. and brash-filled ship track were observed

south of Neebish Island. There were also scattered areas of snow on

the ice. Along the west side of Sugar Island up to Sault Ste. Marie,

the river contained shore ice and brash. Low concentration of brash

was also observed from the mouth of the river to the southern tip of

St. Joseph Island.

By the third week in January. the river was completely ice covered,

with the exception of a few open water areas in the vicinity of the

locks and in the river channel. The last ship passed through the

locks at Sault Ste. Marie on February 6. 1974. ending a navigation

Season that had started on March 28, 1973.

The river remained ice covered through early lK.arch with little signs

of decay. On March 4. it was observed to be still completely ice

covered (fig. A.29~ and a refrozen ship track could be seen its

entire length. The first ship passed upbound through the locks on

April 2, 1974. The ice cover on the northern part of the river started

breaking up in early April, parttally due to ship'traffic and icebreaking activities. By mid-April. the ice cover on the southern half of

the river was also showing signs of decay as icebreaking activity and

mild weather took their toll. For all practical purposes. the river

was ice free by May 1, 1974.

4.5 Lake Michigan

Visual aerial ice reconnaissance flights were made over the northern

porl:ions of Lake M.ichigan on February 27 (fig. A.30) and March 4 (fig.

A.31). The general areal pattern of ice cover given below is based

primarily on ice charts.

Ice began forming in the Straits of Mackinac and in Green Bay by

mid-December. as shown in figure A.6. Much below normal temperatures

the first 2 weeks in January, indicated by the upward slope 9f the

freezing degree-days graphs on figure A.2, resulted in extensive ice

cover formation in Green Bay, the Straits of Mackinac west to Beaver

Island, and in the south end of the lake, as shown in figure A.lO.

Above normal temperatures the last half of January resulted in loss of

ice cover on the southern lake area and little net change in lakeward

e..xtent of ice in the northern end of the lake as evidenced by figures

8
A.ll and A.lt. Ice began forming in mid-lake areas of the northern end

of the lake in the first half of February, resulting in maximum ice

extent with ice covering an estimated 20 percent of the lake's surface

(see fig. A.13 thr6ugh A.15). By February 17, freezing degree-day accumulations for Green Bay and Milwaukee were over 85 percent of their maximum value for 1973-74.

During maximum ice cover, ice extended from the north entrance of

Green Bay to Grand Traverse Bay. Green Bay and the Straits of Mackinac

to Beaver Island weTe completely ice covered, while most of the open

lake north of a line from Escanaba to Charlevoix was 70-to 90-percent

ice covered. In the south end of the lake, shore ice of five- to

seven-tenths concentration extended from Milwaukee southward.

On February 27, the following ice cond:l.tions weTe observed on a

fllght over the north end of the lake. Green Bay and the Straits of

Mackinac had a snow-covered ice sheet. West of the solid ice in the

Straits, brash ice of various concentrations lined the shore extending

to the vicinity of Manistique, Mich. The lake to the east of Beaver

Island contained brash of decreasing concentration southward.

Unseasonably mild weather in the first half of March. evi.denced ty

the downward slope of the freezing degree-day graphs for Lake Michigan

(fig. A.2). resulted in loss of ice in mid-lake areas at the north end

of the lake. On March 17. the bulk of the ice was located in Green Bay

and the Straits. Ice in these are.t\s was $radually lost over the next

month. By mid-April (fig. A. 23). Lake Michigan was essentially ice free

4.6 Lake Huron

Visual aerial ice reco~~issance flights were made over Lake Huron

on February 25. 27, and March 4. Observed ice conditions on these dates

are portrayed in figures A.32 through A.34.

Bays and harbors had begun to freeze over by the third week of

December. By the end of the first week of January. Saginaw Bay was

ice covereil, and the Straits east to Cheboygan. Mich., were 70- to 90-

percent ice covered. Although ice cover continued to increase through

the second week in January, mild temperatures retarded ice growth during

the second half of January. In February, ice formed over the open areas

of Lake Huron. and the lake was· estimated to be near maximum ice cover

between February 10 and 24. During that period, the lake was estimated

to be 65-percent ice covered. On February 24, freeZing degree-day

accumulations at Alpena were 88 percent of the maximum season value.

An intense ~inter storm mOVed over the Great Lakes on February 22 and

23, causing significant changes in ice-cover ,concentration and distrib~­

tion. On February 27 (fig. A.34). the following ice conditions were observed: the Straits to Cheboygan had snow-covered ice, while a mixture

of thin and thick ice covering 70 percent of the lake's surface extended

9
east of Bois tlanc l<;lan1 over much of the lake north c.f a line from

Alpena to De Tour and along the ncr-til short" from De Tour eastward.

Brash io: c,f lessf>r ('oncentrations was located lakeward of the ice

along the north shore. FrOlll AlpenA sOOJthward, ice of six- to eighttenths concentration was lo~ated along the shore beyond an open water

area from Alpena to HarrisvIlle. The north end of Saginaw Bay was tentenths ice.covered and a lead was observed along the northeast shore.

Beyond the solid jce in the bay,'brash, covering 10 percent of the area,

continued eastward many miles into the lake.

Ice cover, in genera], decreased in lfarch due to mile temperatures.

FreezIng .'egree-days at Alpena (fig. A.3) had a negative slope the week

ending March 10, indicating a thaw period. By Apr!.l 7, the only area

. \lith significant lee coy"r was the northeast part of the lake. inclllding North Channel and Georgian Bay. By the fourth ~leet; of Apr~.l. the

ice in thes~ northern areas was deteriorating rapidly.

4.7 St. Clair River and Lake S!:. Clair

Ice charts w~re produced for the February 5 and 25 flights over

the St. Clair River and Lake St. Clair (fi~. A.35 and A.36).

Ice was first reported on the St. Clair ~iver on December 17.

Above. freez:l:l8 tel'.lperatures during the last ~7eek of Decetnber, hoyever.

made the rciver virtcally :lee free by the end of that month. Another

period of ice formation started in early January and continued through

the secorul week of that month. A thaw period starting the third week

of the month. reminiscent of the. January 1973 tb3w, resulted in icefree condltions on the river hy late January.

Low temperature returned during the first 2 weeks of February.

causing rapid ice formation on both southern Lake Huron and the St.

Clair River. An ice bridge was obs~rved at Port Huron on February 5.

On that date, the river was estimated to be seven- to nine-tenths ice

covered and an ice jam was observed in the vicinity of Algonac. 011

February 25. the river was 30 to 40 percent covered with newly formed ice

between Algonac and Stag Island. The upper river, north of Stag Island,

had only shore ice. while southern Lake Huron was estimated to be 90-

percent ice covered.

Unusually mild weather in early March brought an end to significant

ice cover on the St. Clair River. The river was virtually ice free on

March 3. although a cold spell March 24 to 26 brought widespread new

ice formation of short duration. The last report of ice on the river

was dated March 30.

Ice was first reported on Lake St. Clair on December 16. By January

6, the lake had a complete ice cover. As can be seen from figure A.4,

above normal temperatures the last half of January, indicated by the

10
freezing degree-day graphs for Detroit and Cleveland, caused deterioration of the ice cover. By the last week of the month (fig. A.12), Lake

St. Clair had less ice than normal.

Ice covered the entire lake in early.February; and on a flight on

February 5 (fig. A.35) the lake had a medium-thick ice sheet with snow

covering 20 to 30 percent of the ice in mid-lake.

The lake retained its complete ice cover until the last week of

February (fig. A.36). when mild weather caused deterioration of the ice

cover. Mild temperatures dominated the first half of March. The lake

was for the most part ice free by March 10, as shown on figure A.18,

although some new ice formed during the last half of March (fig. A. 20).

Last reports of ice clUlle from the north end of the lake on March 25.

4.8 Lake Erie

Lake Survey Center personnel made one flight over Lake Erie in late

February (fig. A.37).

The bays and harbors in western Lake Erie began to freeze over in

mid-Decembe~ as shown on figure A.6, with the last ship passing through

the Welland Canal on December 31. The perimeter and western end of the

lake were the main areas of ice forma.tion-in .January. A thaw the second

half of that month caused reduction of ice cover so that by .January 27

(fig. A.12) the main body of ice was located along the north shore of

the western end of the lake. Ice began forming over the entire lake

the first week in February, and by February 10 (fig. A.14) the lake was

near lllaXimum ice cover. Ice cover neared the lllaXimum extent intertrlttently during the last 3 weeks of February in resp,onse to changing

weather conditions. Freezing degree-day accumulation at Cleveland was

approximately 80 percent of its maximum value on February 17 (fig. A.4).

On February 25. the lake was estimated to be 95-percent ice covered. A

zone of thin and new ice was observed along the northern shore on that

date. Medium-thick ice with a 30- to 40-percent snow cover was observed

lakeward of the thin ice. The rest of the lake's perimeter was observed

to have medium-thick ice of nine- to ten-tenths concentration with variable snow cover.

The ice cover decreased in extent in early March, and by mid-month

(fig. A 19). there was very little ice left. An area of ice persisted

in the eastern end of the lake through the end of March. The Welland

Canal opened on March 29, 1974, and the last report of ice came from

Buffalo, N. Y., on April 4.

11
4.9 Lake Ontario

Figure A.38 portrays observed ice conditions on eastern Lake Ontario

for February 15 and is based on a Lake Survey Center ice reconnaissance

flight made over that area.

Low temperatures the second and third weeks of December brought ice

formation to the bays in Lake Ontario with the St. Lawrence Seaway

closing on December 20, 1973. The last week in December was mild with

temperatures for the week averaging above freezing at Rochester,

N. Y., as evidenced by the downward slope of the f~eezing degree-day

graph in figure A.5. December's temperature pattern was repeated in

January as the first half of that month had low temperatures followed

by milder weather the last half. As a result, the ice cover. which was

most prominent in the northeast area of the lake, advanced and retreated

in January as shown in figures A.lO and A.ll. Low temperatures the second and third weeks of February coincided with the period of maximum ice

cover on Lake Ontario. On February 17, freezing degree-day accumulation

at Rochester was at 98 percent of its seasonal maximum. Two days earlier, February 15. the lake was estimated to be 25-percent ice covered.

The ice conditions illustrated in figure A.39 were observed on a

flight over the lake on February 15. Thin ice of four- to five-tenths

concentration was observed from Rochester to Oswego, N. Y., ranging

3 to 8 mileS (5 to 13 km) into the lake from shore. A semi-circular shaped zone of complete ice cover paralleled thp shore from

the southeast and of the lake to the northeast shore. Lakeward, a

mixture of thin and medium ice of nine-tenths conoentration and a zone

of brash ice beyond that extended many miles into the lake. Thick SllOWcovered ice extended from bays and harbors to the islands in the northeast end of the lake, while a light dusting of snow covered much of the

ice surface along the southeast shore.

Much of· the ice in the open lake was gone by early l.farch as mild

weather, evidenced by the sharp drop in freeZing degree-day accumulation in figure A.5, caused deterioration of the existing ice cover.

By early ~mrch (fig. A.17). the bulk of the open lake ice was gone.

Lower temperatures the last half of the month helped preserve existing

ice cover. The last report of ice came from Cape Vincent, N. Y., and

was dated March 29.

The St. Lawrence Seaway opened on March 26. recording the earliest

opening date in its IS-year history.

12
5. ACKNOWLEDGMENTS

Lake Survey Center visual aerial ice reconnaissance activities were

carried out under the general guidance of Dr. L. Bajorunas, Chief of

Limnology Division, and Dr. F. H. Quinn, Chief of the Lake Hydrology

Group. and were under the supervision of C. Adams of the Lake Hydrology

Group. Ice observers included C. Adams, G. Leshkevich. and M. Eisenstat.

Flight support was provided by the U.S. Coast Guard. Ninth District

(U.S.C.G. Air Stations, Detroit, Mich., and Traverse City, Mich.) •.

Climatological data used in this report were taken from the U.S.

Department of Commerce publication Weekly Weather and Crop Bulletin.

13
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Composite ice chart - !J)eek endingJcmuarry 27. 1974.

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Figure A.20. Composite ice chart - week ending March 24, 1974.

legend

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