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NOAA Technical Memorandum GLERL-125

GREAT LAKES ICE COVER, FIRST ICE, LAST ICE, AND ICE DURATION: 

WINTERS 1973-2002

Raymond A. Assel

NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI 48105

Great Lakes Environmental Research Laboratory

Ann Arbor, Michigan 

September 2003

UNITED STATES

DEPARTMENT OF COMMERCE

Donald Evans

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Conrad C. Lautenbacher, Jr.

Administrator
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NOTICE

Mention of a commercial company or product does not constitute an endorsement 

by the NOAA. Use of information from this publication concerning proprietary 

products or the tests of such products for publicity or advertising purposes is not 

authorized. This is GLERL Contribution No. 1285.

This publication is available as a PDˇ file and can be downloaded from GLERL’s 

web site: www.glerl.noaa.gov. Hard copies can be requested from GLERL, 

Information Services, 2205 Commonwealth Blvd., Ann Arbor, MI 48105.

pubs.glerl@noaa.gov.

ACKNOWLEDGMENTS

This work was funded in part by NOAA’s Earth System and Data Information 

Management program. The NIC and the CIS provided the historic ice charts. Mr. David 

Norton’s (GLERL) contributions during the data reduction and quality control phases 

of this project were critical for its successful completion. University of Michigan’s 

Cooperative Institute for Limnology and Ecosystems Research (CILER) staff; D. Meyers, 

B.A. Hibner, N. Morse, P.J. Trimble, K. Cronk, and M. Rubens and GLERL staff; Ms. 

Deborah Lee, provided invaluable contributions to this project.
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Table of Contents

ABSTRACT........................................................................................................................................................... 7

1. INTRODUCTION ........................................................................................................................................ 7

2. BASIC DATA AND ANALYSIS METHODS ............................................................................................. 7

 2.1 Averages and Extremes over the 30-winters........................................................................................... 8

 2.2 Spatial averages for specific depth ranges.............................................................................................. 8

3. RESULTS AND DISCUSSION..................................................................................................................... 9

 3.1 Analysis Reslts........................................................................................................................................ 9

 3.2 Long-Term Average and Trends of ˇirst Ice Dates................................................................................ 9

 3.3 Extreme Dates of ˇirst Ice .................................................................................................................... 10

 3.4 Long-Term Average and Trends of Last Ice Dates............................................................................... 10

 3.5 Extreme Dates of Last Ice..................................................................................................................... 11

 3.6 Long-Term Average and Trends of Ice Duration ................................................................................. 11

 3.7 Extreme Ice Duration............................................................................................................................ 12

4. SUMMARY AND OBSERVATIONS......................................................................................................... 13

 4.1 Lake Bathymetry................................................................................................................................... 13

 4.2 Temporal Trends................................................................................................................................... 14

 4.3 ˇuture Ice Cover ................................................................................................................................... 14

6. REˇERENCES ............................................................................................................................................. 14

Figures

ˇigure 1a. Lake Bathymetry............................................................................................................................. 16

ˇigure 1b. Average ˇebruary Air Temperatures (0C )...................................................................................... 16

ˇigure 1c. Place names of the Great Lakes...................................................................................................... 17

ˇigure 2a. Combined Great Lakes inter-annual variations in the percent of depth range (≤ 20m) 

with ice at the ≥ 90% and with ice at the ≥ 10% ice concentration threshold values..................... 18

ˇigure 2b. Combined Great Lakes inter-annual variations in the percent of representative mid-lake 

depth rangewith ice at the ≥ 90% and the ≥ 10% ice concentration threshold values.................... 18

ˇigure 2c. Same as 2a but for Lake Superior................................................................................................... 19

ˇigure 2d. Same as 2b but for Lake Superior................................................................................................... 19

ˇigure 2e. Same as 2a but for Lake Michigan ................................................................................................. 20

ˇigure 2f. Same as 2b but for Lake Michigan ................................................................................................. 20

ˇigure 2g. Same as 2a but for Lake Huron .......................................................................................................21
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ˇigure 2h. Same as 2b but for Lake Huron..........................................................................................................21

ˇigure 2i. Same as 2a but for Lake Erie..............................................................................................................22

ˇigure 2j. Same as 2b but for Lake Erie .............................................................................................................22

ˇigure 2k. Same as 2a but for Lake Ontario........................................................................................................23

ˇigure 2l. Same as 2b but for Lake Ontario........................................................................................................23

ˇigure 3a. Thirty-winter average dates of first reported ice at the ≥ 90% threshold value .................................24

ˇigure 3b. Spatial averaged dates of first ice for the shore area (0-20 m depth range) and mid lake 

area (101-200 m depth range). The horizontal black lines are the 30-winter averages .....................24

ˇigure 3b-1. Same as 3b but for Lake Superior....................................................................................................25

ˇigure 3b-2. Same as 3b but for Lake Michigan ..................................................................................................25

ˇigure 3b-3. Same as 3b but for Lake Huron .......................................................................................................25

ˇigure 3b-4. Same as 3b but for Lake Erie...........................................................................................................25

ˇigure 3b-5. Same as 3b but for Lake Ontario .....................................................................................................25

ˇigure 3c. Winter 1977 spatial distribution of dates of first reported ice at the ≥ 90% ice threshold.................26

ˇigure 3d. Thirty-winter composite minimum (earliest) dates of first reported ice at the ≥ 10% ice 

threshold .............................................................................................................................................26

ˇigure 3e. Winter 1998 spatial distribution of dates of first reported ice at the ≥ 90% ice threshold.................27

ˇigure 3f. Thirty-winter composite maximum (latest) dates of first reported ice at the ≥ 10% ice threshold....27

ˇigure 4a. Thirty-winter average dates of last reported ice at the ≥ 90% threshold value ..................................28

ˇigure 4b. Spatial averaged dates of last ice for the shore area (0-20 m depth range) and mid lake area 

(101-200 m depth range). The horizontal black lines are the 30-winter averages.............................28

ˇigure 4b-1. Same as 4b but for Lake Superior....................................................................................................29

ˇigure 4b-2. Same as 4b but for Lake Michigan ..................................................................................................29

ˇigure 4b-3. Same as 4b but for Lake Huron .......................................................................................................29

ˇigure 4b-4. Same as 4b but for Lake Erie...........................................................................................................29

ˇigure 4b-5. Same as 4b but for Lake Ontario .....................................................................................................29

ˇigure 4c. Winter 1994 spatial distribution pattern of dates last reported ice at the ≥ 90% ice threshold..........30
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ˇigure 4d. Thirty-winter composite maximum (latest) dates of last reported ice at the ≥ 10% ice threshold ..30

ˇigure 4e. Winter 1998 spatial distribution pattern of dates last reported ice at the ≥ 90% ice threshold .......31

ˇigure 4f. Thirty-winter composite minimum (earliest) dates of last reported ice at the ≥ 10% ice 

threshold...........................................................................................................................................31

ˇigure 5a. Thirty-winter average ice duration at the ≥ 90% threshold value....................................................32

ˇigure 5b. Spatial averaged ice duration for the shore area (0-20 m depth range) and mid lake area 

(101-200 m depth range). The horizontal black lines are the 30-winter averages...........................32

ˇigure 5b-1. Same as 5b but for Lake Superior....................................................................................................33

ˇigure 5b-2. Same as 5b but for Lake Michigan ..................................................................................................33

ˇigure 5b-3. Same as 5b but for Lake Huron .......................................................................................................33

ˇigure 5b-4. Same as 5b but for Lake Erie...........................................................................................................33

ˇigure 5b-5 .Same as 5b but for Lake Ontario ....................................................................................................33

ˇigure 5c. Winter 1997 spatial distribution pattern of ice duration at the ≥ 90% threshold.............................34

ˇigure 5d. Thirty-winter composite maximum ice duration at the ≥ 10% ice threshold ..................................34

ˇigure 5e. Winter 1998 spatial distribution pattern of ice duration at the ≥ 90% threshold.............................35

ˇigure 5f. Thirty-winter composite minimum ice duration at the ≥ 10% ice threshold ...................................35

TABLES

Table 1. Distribution of Ice Charts by Winter Season...................................................................................36

Table 2.1. Great Lakes statistics for discrete depth ranges for ice cover concentration ≥ 90% .......................37

Table 2.2. Lake Superior statistics for discrete depth ranges for ice cover concentration ≥ 90%....................38

Table 2.3. Lake Michigan statistics for discrete depth ranges for ice cover concentration ≥ 90% ..................39

Table 2.4. Lake Huron statistics for discrete depth ranges for ice cover concentration ≥ 90% .......................40

Table 2.5. Lake Erie statistics for discrete depth ranges for ice cover concentration ≥ 90%...........................41

Table 2.6. Lake Ontario statistics for discrete depth ranges for ice cover concentration ≥ 90% .....................42

Table 3.1. Great Lakes statistics for discrete depth ranges for ice cover concentration ≥ 10% .......................43

Table 3.2. Lake Superior statistics for discrete depth ranges for ice cover concentration ≥ 10%....................44

Table 3.3. Lake Michigan statistics for discrete depth ranges for ice cover concentration ≥ 10% ..................45
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Table 3.4. Lake Huron statistics for discrete depth ranges for ice cover concentration ≥ 10% .......................46

Table 3.5. Lake Erie statistics for discrete depth ranges for ice cover concentration ≥ 10%...........................47

Table 3.6. Lake Ontario statistics for discrete depth ranges for ice cover concentration ≥ 10% .....................48

Table 4. ˇrequency of Winters Without ˇreeze-up at the west arm of Grand Traverse Bay ........................49
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Great Lakes Ice Cover, First Ice, Last ice, and Ice Duration: Winters 1973-2002

Raymond A. Assel

ABSTRACT. A 30-winter digital ice cover data set consisting of 1210 ice charts was established 

for the Great Lakes. The data set is an update of a 28-winter data set given in Assel et al. (2002). 

The temporal and spatial distribution patterns of the dates of first ice, dates of last ice, and ice 

duration over the 30-winter base period are analyzed for the combined Great Lakes and for each 

Great Lake over the 30-winter period. Average and the composite extremes over the 30 winters 

are presented. Analysis methods are described, and results are summarized in a series of plots, 

charts, and tables. The complete data set is available as part of an official National Oceanic and 

Atmospheric Administration Atlas (Assel, 2003).

1. INTRODUCTION

This cryosphere is an important indicator of climate and climate change (ˇitzharris et al., 1996, Magnuson et al., 

2000), and lake ice is a sensitive index of regional winter climate (Assel and Robertson, 1995). Therefore, the 

availability of improved information on Great Lakes ice is timely. This is the first of a series of reports presenting various aspects of an analysis of a 30-year digital ice cover data set, updated from Assel et al, (2002). In this 

report, the results of an analysis of the dates of first ice, dates of last ice, and ice duration over a 30-winter base 

period are presented. The data is described, analysis methods are documented, and results are presented. Temporal 

and spatial trends are briefly discussed within the context of lake bathymetry (ˇig. 1a), which is a proxy for lake 

heat storage, and winter air temperature (ˇig. 1b), which is a proxy for heat loss at the lakes surface. Place names 

are given in ˇigure 1c. This report and data in Assel (2003) provides a baseline of Great Lakes ice cover and ice 

cover variation during the late 20th and early 21st centuries and supersedes Assel et al., 1983. The information 

given here and in Assel (2003) has applications to research, education, engineering, and operational planning and 

activities. Recent studies in which Great Lakes ice was a factor considered include climate (Lofgren et al., 2002), 

fish recruitment (Brown et al., 1993), and the winter aquatic system (Nicholls, 1998; Magnuson et al., 1997).

2. BASIC DATA AND ANALYSIS METHODS

The data used in this analysis is ice concentration, that is the fraction of a unit of lake surface area that is completely covered with ice. The ice concentration is contained in a grid matrix of 510 rows x 516 columns, making 

a total of 263,160 grid cells; each grid cell has a nominal resolution of 2.5 km x 2.5 km (Assel et al., 2002). There 

are 38,203 over-water cells and 224,957 land cells. There are a total of 1210 grids over the 30-winter seasons. 

These data were partitioned by winter season (Table 1) and an analysis for threshold ice concentration values of 

dates of first/last ice each winter, and ice duration (the difference between these dates) was made for each winter 

season. The original ice charts had ice concentration recorded to the nearest 10%. A preliminary analysis using 

discrete 10% values or ranges, on the date ice was first observed produced incoherent spatial patterns and was 

therefore not used. Instead, the analysis was made on nine overlapping threshold ice concentration values in 10% 

increments starting from ice concentration ≥10%, and ending at ice concentrations ≥90% (≥10%, ≥20%, ≥30%, 

≥40%, ≥50%, ≥60%, ≥70%, ≥80%, ≥90%). These threshold values corresponding to ranges of ice concentration 

as shown in the box below. This approach produced spatially coherent patterns. If one wanted to examine the 

10% ice concentration pattern (for dates of first/last ice or ice duration) it could be done by taking the differences 

between the ≥10% and ≥20% ice concentration. This same is true of any other adjacent ice concentration range.

The dates of observed first/last ice may not be the actual date that ice first formed and actual last date of ice 

because this analysis is limited by the dates of the first and last ice charts of each winter. However, it is likely that 

for most of the lake’s surface area that the actual date of first ice occurred somewhere between the date of the first 

ice chart, and the ice chart that has the observed threshold value of ice concentration. This is true because on the 

date of the first ice chart, most of the Great Lakes are usually open water. A similar comment is true for the date 

of last ice cover. The dates of first/last ice reports each winter and the percent ice cover on the date of first/last 
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ice reports are given in Table 1. The lake-averaged percentage of ice cover 

on the first and last ice chart is under 5% for most winters, and the number 

of days between ice charts each winter varied from 2 to 7 days (Assel et al., 

2003). The estimates for date of first/last ice each winter is, in general, representative for most threshold ice concentrations for most of the surface area of 

the Great Lakes within these limits.

2.1 Averages and Extremes Over the 30-Winters

The average date of first/last ice and average days of ice duration and the 

composite maximum and minimum of these variables were calculated from 

the 30 annual grids respectively. If less than 14 winters met the threshold ice 

concentration value for a given grid cell, then that grid cell was not included 

in the calculation of the 30-winter average. The composite maximum date of 

first ice cover is an observed climatic limit for the latest date of first ice cover, and the composite minimum is an 

observed climatic limit for the earliest date of first ice cover at each grid cell. In a similar fashion, the composite 

maximum for the last date of ice cover for a given ice concentration threshold value is an observed climatic limit 

of the latest date of last ice cover concentration for a given ice concentration threshold value, and the minimum 

for the last date of ice cover is the climatic limit for the earliest date of last ice cover. The composite maximum 

and minimum duration are the observed limits of ice cover duration over the 30-winter period. 

2.2 Spatial Averages for Specific Depth Ranges

The dates of first/last ice and ice duration for the ≥90% ice concentration threshold and for the ≥10% ice concentration threshold were related to lake bathymetry by a grid of water depths that is coincident with the ice cover 

grid. The spatial average ice concentration for each winter season was calculated for the following depth ranges: 

>0 m and ≤20 m, >20 m and ≤50 m, >50 m to ≤100 m, >100 m to ≤200 m, and >200 m. The ≥90% (Table 2) 

and the ≥10% (Table 3) ice concentration threshold values were chosen for analysis here because they bracket the 

entire range of possible dates of first/last ice and days of ice cover duration. The ≥10% ice concentration threshold 

represents the ice edge boundary, concentrations below10% are defined as “open water” (World Meteorological 

Organization, 1970). The ≥90% ice concentration threshold is an upper limit of ice concentrations, corresponds 

to the WMO definitions for very closed pack (>90% but <100% ice concentration) and consolidated pack ice 

(pack ice that is 100% ice concentration), (World Meteorological Organization, 1970). These two extremes have 

obvious implications for winter navigation in the Great Lakes. The values of all other ice concentration threshold 

values are between these two extremes. 

In making the calculation of the depth range spatial average (date: first/last ice or days ice duration) over all grid 

cells for a given depth range if the ice concentration for a grid cell in that depth range was below the threshold ice 

concentration value it was not included in the calculation. Including grid cells below the ice concentration threshold values would result in an underestimation of the area averaged value (earlier for first/last ice and shorter for 

ice duration) for that ice concentration threshold and depth range. However doing the calculations without these 

cells makes it difficult to compare values for different years because the number of grid cells, and thus the area 

meeting the threshold ice concentration for a given depth range, is different each year. Therefore in order to help 

interpret the significance of the depth averages (dates of first/last ice and ice duration) the number of cells for the 

>0 m and ≤20 m depth range (ˇig. 2a) and for the >100 m and ≤200 m depth range (ˇig. 2b) for which the ice 

concentration threshold value (for the ≥90% and ≥10% ice thresholds) is observed each winter for the combined 

area of the Great Lakes is given as a percent of the total number of grid cells for each depth range. Similar plots 

were produced for Lakes Superior (ˇig. 2c, 2d), Michigan (ˇig. 2e, 2f), Huron (ˇig. 2g, 2h), Erie, (ˇig 2i, 2j), and 

Ontario (ˇig. 2k, 2l).

 Range Threshold

 0% to 9% none

10% to 100% ≥10%

20% to 100% ≥20%

30% to 100% ≥30%

40% to 100% ≥40%

50% to 100% ≥50%

60% to 100% ≥60%

70% to 100% ≥70%

80% to 100% ≥80%

90% to 100% ≥90%
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3. PRESENTATION OF RESULTS AND DISCUSSION

3.1 Analysis Results

The complete analysis results are available in Assel (2003). That data set is given as fixed formatted ASCII 

grids and as ice chart graphics that portray spatial pattern of first/last ice dates and ice duration for each ice 

concentration threshold value for each winter season, and are not given here for the sake of brevity. Here we 

present selected results from that publication and we present the results of the bathymetry and lake averaged 

analysis that is not given in Assel (2003). Table 2.1 to Table 2.6 and Table 3.1 to Table 3.6 can be used to identify 

inter-annual variations, the extremes, and typical values of the dates of first/last ice and ice duration for selected 

combinations of depth range and ice concentration threshold value for the ≥90% (Tables 2) and the ≥10% (Tables 

3) threshold values, for the combined Great Lakes (Table 2.1 and Table 3.1) and for each Great Lake (Tables 

2.2-2.6 and Tables 3.2-3.6). Thus, using ˇig. 2, Table 2, and Table 3 one can evaluate the severity of any given 

winter season (in this data set or other winters) relative to dates of first/last ice and ice duration and place it into 

historical context.

Here we use charts and line graphs of the ≥90% and the ≥10% threshold values in the discussion of the spatial 

and temporal distribution patterns of first/last ice and ice duration. The spatial pattern for other ice concentration 

threshold values is similar to these two thresholds. The discussion below is limited to temporal and spatial 

patterns of first/last ice dates and ice duration for the >0 and ≤20 depth range, which is representative of the shore 

area of the Great Lakes and depths representative of the deeper mid-lake areas of the Great Lakes (different for 

each Great Lake). Those readers who wish to examine values for other discrete depth ranges noted above are 

referred to Tables 2 and Tables 3.

3.2 Long-Term Average and Trends of First Ice Dates

The spatial pattern of the 30-winter average date of first reported ice cover is portrayed in ˇig. 3a. Mid-lake areas 

of Lakes Superior (Table 2.2, 101-200 m), Huron (Table 2.4, 101-200 m), and the northern section of Michigan 

(Table 2.3, 101-200 m) form ice cover ≥90% during ˇebruary. However, on the long-term average ≥10% 

threshold plot of dates of first ice (not shown but similar to ˇig. 3a), there are areas in Lakes Michigan, Huron, 

and Ontario that are open water. These open water areas are largest for Lakes Michigan and Ontario where they 

cover virtually the entire mid lake area. This pattern is attributed to the combination of lake bathymetry (ˇig. 1a), 

and winter air temperatures (ˇig. 1b). Lake Michigan has a large north to south extent, and air temperatures are 

usually milder in the southern end of that lake. Only during winters when much-below average air temperatures 

extend to the southern end of that lake for much of the winter will Lake Michigan form extensive mid lake ice 

cover (Assel and Quinn, 1979). Lake Ontario is the eastern most and second southern most of the Great Lakes, so 

that winter air masses approaching from the north and west are moderated by movement over the open waters of 

Lakes Superior, Huron, and Michigan, and this, in combination with the large mean depth of Lake Ontario (86 m), 

results in less extensive ice cover most winters (Assel et al., 2003). The perimeter of the Great Lakes, and all of 

Lake Erie because it is so shallow, develop ice cover ≥90% during January (Tables 2.1-2.6, 0-20 m). The shallow 

bay areas north of about 43.50N form ice covers ≥90% in December (ˇig 3a).

The 30-winter average date of first ice for the Great Lakes as a whole varies from ˇebruary 9 for mid lake (depths 

101-200 m) to January 14 for shallow areas (depths ≤20 m). The maximum and minimum dates of first ice are 

January 29 and December 24 for the shore area and ˇebruary 26 and January 17 for mid lake area (ˇig. 3b, similar 

plots for each Great Lake are given as ˇig. 3b-1 to ˇig. 3b-5). The minimum date is somewhat misleading in that 

in extremely mild winters such as 1998 (Assel et al., 2000 and 2002) (Assel and Norton, 2002) the mid lake areas 

are virtually ice-free. 

A linear regression analysis of the area (number of grid cells) for specific depth ranges given in ˇig. 2a and ˇig. 

2b for the ≥90% ice threshold show that the area of ice cover expressed as a percent for both the shore and midlake depth ranges has a decreasing trend over the 30 winters, annual rate of decrease is 0.65% for the shore area 
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and 1.31% for the mid lake area. The regression coefficients were significant at the 95% level. A similar analysis 

for the annual dates of first ice (ˇig. 3b) did not have significant regression coefficients. So, the date of first ice 

has not changed significantly, but the area of ice on that date for a given depth range, particularly for mid-lake 

areas has decreased. This is also true for amounts of ice for the dates of last ice since the areas where dates of first 

ice did not meet the threshold ice cover values are also the same for the dates of last ice.

3.3 Extreme Dates of First Ice 

Winter 1977 provides an example of the spatial distribution pattern of dates of first ice when ice formed earlier 

than average (ˇig. 3c). During that winter, dates of first ice in the mid lake area was January 22 and the shore 

areas it was December 26, both of these dates are about 3 weeks earlier than their respective 30-winter averages. 

The mid lake area of ice at the ≥90% threshold value was also much large than average (ˇig 2b). Other winters 

for which the area of ice at the ≥90% threshold value for water depths between 100 m and 200 m was also much 

larger than average include 1978, 1979, and 1994. The average date of first reported mid-lake ice for these three 

winters is ˇebruary 15, ˇebruary 3, and January 27, respectively (Table 2.1). Winters in which the shallow lake 

areas (0-20 m) reported first ice, at the ≥10% threshold, earlier than the long-term average date over the Great 

Lakes as a whole includes winter 1977 (December 22) and winter 1990 (December 20) see Table 3.1.

The composite minimum (earliest) date of first ice at the ≥10% threshold (ˇig. 3d) shows that ice formed in the 

shallows of the Great Lakes in December. However, the composite over the 30 winters for mid-lake areas was a 

no-ice condition, that is these areas were open water during one or more of the 30-winter base period. 

Winter 1998 provides an example of the spatial distribution pattern of dates of first ice during a winter when 

ice formed later than average (ˇig. 3e). Mid lake areas were open water, and ice formed in bays and the Straits 

of Mackinaw during January. This pattern is remarkably similar to ˇig. 3d, the composite minimum over the 

30-winters, but in 1998 it occurred a month later. Other winters with much-below average areas of mid-lake ice 

formation for the Great Lakes as a whole (ˇig. 2b) include the winters of 1983, 1987, 1999, 2000, and 2002. 

Thus, the dates in Tables 2.1 and Table 3.1 for these winters are not important because the mid-lake areas, and 

to a lesser degree the shore areas, were primarily ice-free those winters. Other winters with relatively low midlake ice covers include winters 1975, 1976, 1995, and 2001. The extreme (climatic composite) latest date of first 

ice, for winters in which ice formed (ˇig. 3f, ice ≥10%), occurred primarily in ˇebruary and March with ice in 

small sporadic areas in April. The latest dates of first ice occur in January in the west end of Lake Erie, all of 

Lake St. Clair, and the shallow areas of Lakes Superior, Huron, and Michigan (Lake Huron -- Saginaw Bay, east 

shore areas of Georgian Bay and North Channel; Lake Michigan -- Green Bay; Lake Superior -- shore areas of 

Whitefish Bay, the Apostle Islands, and Thunder, Black, and Nipigon Bays along the north central shore. 

3.4 Long-Term Average and Trends Of Last Ice Dates

Ice loss (last reports of ice) is primarily a function of the energy balance at the lakes surface, which is relatively 

uniform; while the date of ice formation is affected by temperature decline of the entire water column, which is 

influenced by lake bathymetry. This is reflected in a smaller difference in the average date of last reported ice 

between the shore area and mid-lake areas (March 15, March 7, respectively, Table 2.1) relative to the average 

dates of first reported ice for the shore and mid-lake areas (January 14, ˇebruary 9, respectively, Table 2.1). 

Thus, for Lakes Superior and Huron, the spatial pattern of the average date of last ice cover (ˇig. 4a) does not 

correspond to patterns of lake bathymetry (ˇig. 1a) as well as the 30-winter average date of first ice (ˇig. 3a). 

The average dates of last reported ice occur during the month of March over most of Lakes Superior, Huron, 

and Erie with some shore areas losing their ice during April (Lake Superior -- the Apostle Islands, and Thunder, 

Black, Nipigon, Whitefish, and Keweenaw bays; Lake Michigan -- the north tip and south half of Green Bay; 

Lake Huron -- the Straits of Mackinaw, North Channel, east shore of Georgian Bay; Lake Erie -- the extreme 

eastern end of the lake). The average date of last ice ≥90% along the shores of the southern two thirds of Lake 

Michigan occurs in ˇebruary due in part to more moderate air temperatures going southward (ˇig. 1b) 
11

The inter-annual variations in averaged dates of last reported ice for the shore and mid-lake area (ˇig. 4b)1 and 

percent of depth range with ice (ˇig. 2b) have two prominent features: the occurrence of local minima during 

some strong El Nino winters (1983, 1987, and 1998) and the dramatic shift to earlier dates during the last five 

winters of the period of record. The shift to earlier dates during the winters 1998-2002 is in agreement with two 

recent studies of annual maximum ice cover, which indicates the average of the annual maximum ice covers of 

those 5 winters is the lowest 5-winter average in four decades (Assel and Norton, 2002; Assel et al., 2003). This 

suggests a change in the average dates of last ice cover may be occurring in mid lake regions of the Great Lakes. 

However, several more years of observations are needed to confirm that a regime change to earlier dates of last 

ice is indeed taking place.

3.5 Extreme Dates of Last Ice

Winter 1994 provides an example of the spatial distribution pattern of dates of last ice during a severe winter (ˇig. 

4c). During that winter, dates of last ice ≥90% in mid-lake areas and shore areas averaged March 19 and March 

31 respectively, about 2 weeks later than their respective 30-winter averages (Table 2.1). Virtually all of the midlake area (>100 m and ≤200 m) was covered by ice at the ≥90% threshold value that winter (ˇig 2b). Dates of last 

ice at the ≥90% threshold value were in April over the southern two-thirds of Lake Superior, most of Green Bay, 

Grand Traverse Bay, the Straits of Mackinaw in Lake Michigan, North Channel, Georgian Bay, Saginaw Bay 

and the eastern portion of the lake in Lake Huron, the eastern half of Lake Erie, and the extreme east tip of Lake 

Ontario. Last dates of ice in much of the rest of the Great Lakes occurred in March. Winters with similarly late 

average dates of last mid lake ice include 1979, 1996, and 1997 (March 25, March 31, and March 25, respectively, 

Table 2.1).

The 30-winter composite maximum (latest) date of last reported ice (ˇig. 4d, ≥10% threshold) shows that Lake 

Superior is in a class by itself with last dates of ice in May over the western half of the lake and out from the south 

and southeast shore, and dates of last ice in April over the rest of that lake. This is due to lower air temperatures 

in the vicinity of Lake Superior relative to the other Great Lakes. Composite latest last dates of ice also occur in 

May in the northern tip of Green Bay, portions of the Straits of Mackinaw, North Channel, the eastern shores of 

Georgian Bay and the Bruce Peninsula, and in the eastern tip of Lake Erie. Much of the rest of Lakes Huron and 

Erie, northern Michigan, and the east end of Lake Ontario have latest last dates of ice in April. The composite 

maximum (latest) dates of last ice occur in March on the southern half of Lake Michigan and in March and 

ˇebruary on Lake Ontario.

Winter 1998 (ˇig. 4e) is representative of the set of extremely mild winters noted earlier in section 3.3 (winters 

1983, 1987, 1999, 2000, and 2002). During such winters mid-lake areas are virtually ice-free, and less than half 

the shore area have ice cover (ˇig. 2a) so that the dates of last ice (Table 2.1, Table 3.1) represent only a small 

portion of areas associated with the given depth ranges. This is true to a lesser degree for mid-lake areas in 

winters 1975, 1976, 1995, and 2001 (ˇig. 2b). In winter 1998, the last dates of ice ranged from January through 

April and are spatially sporadic (ˇig. 4e). Lake Erie is virtually ice-free; the last dates of ice in Sandusky Bay in 

western Lake Erie occur in January. Last ice in bays and shallow areas in Lakes Superior, Huron, and Michigan 

occur primarily in ˇebruary and March and on northern Lake Superior (Black and Nipigon Bays) into April. 

Winters 1998 and 2002 are remarkable in their similarity to the composite minimum (earliest) date of last ice (ˇig. 

4f). Winter 1998 set new low records for annual maximum ice extent (Assel et al., 2000) and it and winter 2002 

influenced the composite minimum disproportionately. Composite minimum (earliest) last reported ice (ˇig. 4f) 

occurs in ˇebruary and March in bays, shallow lake areas, and in a discontinuous narrow ban along the perimeter 

of the lakes. 

3.6 Long-Term Average and Trends of Ice Duration

The spatial distribution pattern of average duration for ice cover ≥90%, the difference in days between ˇig. 3a

and ˇig. 4a, is portrayed in ˇig. 5a. Ice duration is 90 days or more in the shallow shore areas of the Great Lakes 

1

Similar plots for each Great Lakes are given as ˇig. 4b-1 to ˇig. 4b-5.
12 

(Lake Superior -- Duluth Harbor, the Apostle Islands, Thunder, Nipigon, Black, and Keweenaw bays, and the 

shallow area of Whitefish Bay; Lake Michigan -- Green Bay; Lake Huron -- the St. Marys River, North Channel, 

and the eastern shores of Georgian Bay and Saginaw Bay). Long-term average ice duration of more than 45 days 

but less than 90 days occurs lake-ward of these bay areas and over most of Lake Erie. Ice duration less than 45 

days occurs in the deepest areas of Lakes Superior, Huron, Michigan, and Ontario. The 30-winter statistics for 

depth-averaged ice duration for the entire Great Lakes is given as Table 2.1, summaries for each Great Lake are 

given in Table 2.2 through Table 2.6. The mid-lake areas average 27 days of ice, while shore areas average2 61 

days. The inter-annual range (minimum to maximum) of the spatial average durations2 is 33-89 days for the shore 

area and 2-56 days in the mid-lake area (Table 2.1, ˇig. 5b). The lower than average ice duration in the last 5 

winters (ˇig. 5b) is due primarily to earlier dates of last ice. Plots similar to 5b for each Great Lake, ˇig. 5b-1 to

ˇig. 5b-5, show that the lower than average ice duration during the last 5 winters is most pronounced on Lakes 

Superior (ˇig. 5b-1). Average mid-lake ice duration2 from lowest to highest (ice cover ≥90%) is as follows: Lake 

Michigan 10, Lake Ontario 11, Lake Huron 20, Lake Superior 31, and Lake Erie 43 (ˇig. 5b-1 to ˇig. 5b-5, Table 

2.2 through Table 2.6). Thus, Lake Erie, the most southern of the Great Lakes and exposed to the mildest winter 

temperatures (ˇig. 1b), ironically has the highest ice cover duration, likely due to its shallow depth. Average 

duration2 (for ice cover ≥90%) in the shore region of each Great Lake in order from greatest to least is: Lake 

Huron = 72, Lake Superior = 67, Lake Michigan = 56, Lake Erie = 48, and Lake Ontario = 42. Thus the northern 

Great Lakes (Superior, Huron, and to a lesser degree Michigan) have the greatest duration of shore region ice 

cover, likely because of longer duration of lower air temperatures. 

3.7 Extreme Ice Duration

Winter 1994 (ˇig. 5c) is an example of a spatial pattern of ice cover duration for very severe winter. In 1994 

mid-lake duration (Table 2.1) averaged 52 days, while the shore area ice cover duration averaged 86 days (both 

are about 3� weeks more than the long-term averages of 27 and 61 days, respectively). Winters similar to 1994 

for mid lake ice duration2 include 1977, 1979, and 1996 with 55, 54, and 56 days of mid-lake ice duration (Table 

2.1). Winters similar to 1994 shore ice duration2 include 1977, 1978, 1979, 1984, 1990, and 1996 with 86, 80, 

81, 82, and 89 days of ice duration, respectively. The composite maximum ice duration for ≥10% ice cover (ˇig. 

5d) is shown for comparison. The composite maximum ice duration is between 135 and 180 days in bays and 

shoal areas of Lake Superior -- Thunder, Black, Nipigon, Keweenaw, and Whitefish bays, the Apostle Islands, 

and the southeast shore in the vicinity of Marquette Michigan; Lake Michigan -- north and south ends of Green 

Bay; Lake Huron -- St. Marys River, North Channel, east shore of Georgian Bay, St. Martins Bay in the Straits 

of Mackinaw, and the southern end of the lake in the vicinity of Port Huron; Lake Erie -- the extreme eastern tip 

of that lake. Lake areas with composite maximum durations of 90-135 days include in general all but the deepest 

lake areas (Lake Superior -- the west half and the perimeter of the eastern basin; Lake Michigan -- Green Bay 

and north of a line from the northern entrance of Green Bay to Traverse City then in a band along the eastern 

shore to Muskegon; Lake Huron -- most of Georgian Bay and the perimeter of the main lake extending 5-50 km. 

Composite maximum ice duration of 45-90 days occurs in the remaining mid-lake areas of the Great Lakes with 

the exception of Lake Ontario where maximum ice duration in the rest of its mid lake area is 1-45 days.

Winters with average ice duration less than 1 week (for ≥90% ice cover), are the shortest ice cover duration 

winters for the mid-lake area (100-200 m depth range). These winters include 1987 (3 days), 1998 (2 days), 

2000 (5 days), and 2002 (3 days). Winter 1998 (ˇig. 5e) provides an example of this type of extremely mild 

winter. Winters when the mid-lake ice duration ranged between 1 and 2 weeks are also noteworthy and include 

the winters of 1973 (14 days), 1976 (14 days), 1983 (9 days), 1995 (8 days), and 1999 (8 days). In the shore area 

(less than 20 m depth) winters with average ice duration between 30 and 45 days, the lower extreme of minimum 

ice cover, include 1973 (44), 1975 (43), 1983 (32 days), 1987 (34 days), 1995 (45+ days), 1998 (39 days), 2000 

(38 days), and 2002 (45). Thus, the winters 1983, 1987, 1998, 2000, and 2002 have extremely low ice duration 

in both shore and mid-lake regions of the Great Lakes. These are the winters that likely contributed most to the 

composite minimum ice duration pattern (ˇig. 5f). 

2

Rounded to the nearest whole day.
13

The composite minimum duration exceeds 90 days in Nipigon and Black Bays (Lake Superior), and it exceeds 75 

days in portions of Lake Superior -- Apostle Islands, shallow areas of Whitefish Bay; Lake Huron -- the St. Marys 

River, North Channel, east shore of Georgian Bay, and east shore of Saginaw Bay; Lake Michigan -- the north 

and southern tips of Green Bay. Lake-ward of the these areas ice cover is limited to shallows of the Great Lakes 

where its duration in most cases does not exceed 30 days, exceptions include the Straits of Mackinaw and discrete 

areas of the previously mentioned bays where the duration is up to 60 days. Thus, ice duration is virtually nil over 

most of the open waters of the Great Lakes on the composite minimum ice duration chart (ˇig. 5f).

4. SUMMARY AND OBSERVATIONS

The analysis given in this report provides a climatic baseline of the dates of first/last ice and ice duration for each 

of 30 winters for discrete depth ranges and ice concentration threshold values for the Great Lakes as a whole 

(Table 2.1 and Table 3.1) and for individual Great Lakes (Table 2.2 through 2.6 and Table 3.2 through 3.6). The 

objective is to provide ice cover information in the public, government, and private sectors for research, education, engineering, and operational applications. This report documents analysis methods and supplements the analysis products on the dates of first ice, last ice, and ice duration given in Assel (2003). That data, which is available 

as computer ASCII grid files and plot files, consist of nine threshold values of ice concentration for each winter, 

the 30-winter average, the composite maximum, and composite minimum. 

4.1 Lake Bathymetry

The spatial patterns of dates of first ice are related to lake bathymetry, the shallower areas form ice first as shown 

in ˇig. 3, Tables 2.1, and Tables 3.1. Average date of first ice in shallow waters (up to 20 m depth) is January 8 

and January 14 (for the ≥10% and ≥90% ice concentration threshold values, respectively), while it occurs about 4 

weeks later (ˇebruary 5 and ˇebruary 9 for the ≥10% and ≥90% ice threshold values respectively) for the deeper 

mid lake waters (>100 to 200 m). A representative variation about these average dates over the 30-winter period 

is provided by the 25% and 75% quartiles for January 8 (January 2, January 13), January 14 (January 8, January 

21), ˇebruary 5 (January 29, ˇebruary 9), and ˇebruary 9 ( ˇebruary 4, ˇebruary 16), respectively. Similar 

observations can be made for each Great Lake from the data given in Tables 2.2 through 2.6 (≥90% ice threshold) 

and Tables 3.2 through 3.6 (≥ 10% ice threshold).

The spatial patterns of dates of last ice are not as well related to lake bathymetry, ˇig. 4, as dates of first ice 

because ice ablation is primarily a function of the energy balance at the lakes surface, existing ice cover, and ice 

movement by winds and currents. The average date of last ice varies from March 22 to March 15 in the shallow 

depth regime, and from March 14 to March 7 in the mid lake depth regime, for the ≥10% and ≥90% ice threshold 

values, respectively. Typical variations of these averages over the 30-winter base period as indicated from the 

25% and 75% quartiles are as follows: for March 22 (March 16, March 31), for March 15 (March 10, March 23), 

for March 14 (March 4, March 25) and for March 7 (March 1, March 17), respectively. Similar observations can 

be made for each Great Lake from the data given in Tables 2.2 through 2.6 (≥90% ice threshold) and Tables 3.2

through 3.6 (≥10% ice threshold).

The 30-winter average duration3 of the ice cover, is about twice as long in the shallow depth regime (74 days 

and 61 days for the ≥10% and the ≥90% ice threshold values, respectively) as it is for the mid-lake depth regime 

(38 and 27 days, respectively). The 25% and 75% quartiles of these long-term averages are as follows: for 74 

days (63, 88 days), for 61 days (47, 73 days), for 38 days (22, 53 days) , and 27 days (14, 40 days), respectively. 

Similar observations can be made for each Great Lake from the data given in Tables 2.2 through 2.6 (≥90% ice 

threshold) and Tables 3.2 through 3.6 (≥10% ice threshold).

3

Rounded to the nearest whole day.
14 

4.2 Temporal Trends

A regression analysis of the annual values (winters 1973 through 2002) of the percent ice covered area for the 

Great Lakes surface area bounded by the shore and the 20 depth contour (shore regime), and for that part of 

the lake surface bounded by the 100 and 200 m depth contour (mid-lake regime) for the dates of first reported 

ice cover show average annual declines of 0.65% and 1.31% respectively, over the period of record. The last 

reported dates of ice for the Great Lakes (ˇig. 4b) show two prominent features: (1) earlier dates of ice loss 

during the extremely strong El Nino events of 1983, 1987, and 1998, and (2) a trend for earlier than average 

ice loss dates during the last five winters of record. However, a linear analysis of the dates of first ice, last ice, 

and the magnitude of ice cover duration do not have significant coefficients at the 95% level. Thus, while the 

percent (amount) of ice covered area in the shore regime and mid-lake regime is decreasing the date of occurrence 

apparently is not. The likely reason for this is that ice formation is a discrete event (ice or no ice). If the precursor 

processes needed for ice formation do not occur (the cooling of the entire water column to the temperature of 

maximum density in late fall and early winter, followed by the further cooling of surface mixing layer to the 

freezing point, followed by the loss of the heat of crystallization at the water’s surface) ice formation will not 

occur. 

4.3. Future Ice Cover

It is likely that the annual time series of dates of first ice cover will have a higher frequency of a “no ice” 

condition in the future if global warming continues (Lofgren et al., 2002). This will occur first in the deeper areas 

of the Great Lakes because of their greater heat storage and because of the action of strong winds, which can 

retard or prevent ice formation. In fact, the deeper portions of the Great Lakes do not form ice every winter under 

the current climate as evidenced by winters during the last 30 years in which ice concentration was <10%4, see : 

Lakes Michigan and Huron (Table 3.3 and Table 3.4 for depths >200 m) and Lakes Erie and Ontario (Table 3.5

and Table 3.6 for depths >50 m). 

The record of freeze-up at Grand Traverse Bay on Lake Michigan provides evidence this is also occurring in some 

of the deeper bays of the Great Lakes over the past 30 winters relative to the past 150 winters. The frequency 

of occurrence of winters without freeze-up at the west arm of Grand Traverse Bay is over three times as great 

during the 30-winters 1973-2002 compared to the four consecutive 30 winter periods prior to it (Table 4). And 

freeze-up has only occurred 3 times during the last (1993-2002) 10 winters in Grand Traverse Bay. Thus, instead 

of a smooth linear decline the time series of annual date of first ice might show a “step change” from a” ice” to a 

“no ice” condition. The date of last ice for mid lake regions also provides evidence for a possible “step change” 

to earlier last ice dates (ˇig. 4b). However, more data, at least another decade of observations, is needed to see if 

that pattern will continue. If it does winters with virtually no mid lake ice formation and only sporadic shore ice 

formation such as 1998 and 2002 will become more frequent and perhaps more intense in the 21st Century.

5. REFERENCES

Assel, R. A. An Electronic Atlas of Great Lakes Ice Cover: Winters 1973- 2002. NOAA Atlas. Great Lakes 

Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, Michigan (2003).

Assel, R. A. Ice Records on Grand Traverse Bay. In State of the Bay 2000. The Watershed Center, Grand Traverse 

Bay, 715 East ˇront Street, Traverse City, MI (2001).

Assel, R.A., K. Cronk, and D.C. Norton. Recent Trends in Great Lakes Ice Cover. Climatic Change 57(1):185-

204 (2003).

4

Ice <10% is considered open water and is indicated by “NA” in Tables 3.2 through 3.6.
15

Assel, R.A., and D.C. Norton. Twentieth Century trends in the ice cover of the Laurentian Great Lakes of North 

America. Ice in the Environment: Proceedings of the 16th IAHR International Symposium on Ice, Dunedin, New 

Zealand, December 2-6, 2002. V. Squire and P. Langhorne (Eds.), pp. 321-327 (2002).

Assel, R.A. D.C. Norton, and K. Cronk. A Great Lakes Digital Ice Cover Data Base for Winters 1973-2000. 

NOAA Technical Memorandum GLERL-121. Great Lakes Environmental Research Laboratory, Ann Arbor, MI 

45 pp. (2002). ftp://ftp.glerl.noaa.gov/pubs/tech_reports/glerl-121

Assel, R.A. J.E. Janowiak, D. Boyce, C. O’Connors, ˇ.H. Quinn, and D.C. Norton. Laurentian Great Lakes ice 

and weather conditions for the 1998 El Nino winter. Bulletin of the American Meteorological Society 81(4):703-

717 (2000). http://www.glerl.noaa.gov/pubs/fulltext/2000/20000001.pdf

Assel, R.A. and D. M. Robertson. Changes in winter air temperatures near Lake Michigan during 1851-1993, as 

determined from regional lake-ice records. Limnology and Oceanography 40(1):165-176 (1995).

Assel, R.A., ˇ.H. Quinn, G.A. Leshkevich, and S.J. Bolsenga. Great Lakes Ice Atlas. NOAA Atlas No. 4. Great 

Lakes Environmental Research Lab., Ann Arbor, MI (1983).

Assel, R.A. and ˇ.H. Quinn, 1979. A historical perspective of the 1976-77 Lake Michigan ice cover. Monthly 

Weather Review 107:336-341 (1979).

Brown, R., W. Taylor, and R.A. Assel. ˇactors affecting the recruitment of lake whitefish in two areas of northern 

Lake Michigan. Journal of Great Lakes Research 19:418-428 (1993).

ˇitzharris, B.B. (Editor), Principal Lead Authors: Allison, I, R.J. Braithwaite, J. Brown, P.M.B. ˇoehn, W. Haeberli, K Higuchi, V.M. Kotlyakov, T.D. Prowse, C.A. Rinaldi, P. Wadhams, M.K. Woo, Xie Youyu; Contributing Authors: O.Anisimov, A. Aristarain, R.A. Assel, R.G. Barry, R.D. Brown, ˇ. Dramis, S. Hastenrath, A.G. 

Lewkowicz, E.C. Malagnino, S. Neale, ˇ.D. Nelson, D.A. Robertson, P. Skvarca, A.E. Taylor, and A. Weidick. 

The Cryosphere: Changes and Their Impacts, In Climate Change 1995: Impacts, Adaptations, and Mitigation 

of Climate Change: Scientific-Technical Analysis, Contribution of Working Group II to the Second Assessment 

Report of the Intergovernmental Panel on Climate Change. IPCC. Cambridge University Press (1996).

Lofgren, B.M., ˇ.H. Quinn, A.H. Clites, R.A. Assel, A.J. Eberhardt, and C.L. Luukkonen, C.L. Evaluation of potential impacts on Great Lakes water resources based on climate scenarios of two GCMs. Journal of Great Lakes 

Research 28(4):537-554 (2002).

Magnuson, J.J., D.M. Robertson, B.J. Benson, R.H. Wynne, D.M. Livingston, T. Arai, R.A. Assel, R.G. Barry, V. 

Card, E. Kuusisto, N.G. Granin, T.D. Prowse, K.M. Stewart, and V.S. Vuglinski. Historical Trends in Lake and 

River Ice Cover in the Northern Hemisphere. Science 289:1743-1746 (2002).

Magnuson, J.J.,K.E. Webster, R. A. Assel, C.J Bowser, P.J. Dillin, J.G. Eaton, H.E. Evans, E. J. ˇee, R.I. Hall, 

L.R. Mortsch, D.W. Schindler, ˇ.H. Quinn. Potential Effects of Climate Changes on Aquatic Systems: Laurentian 

Great Lakes and Precambrian Shield Region. Journal of Hydrological Precesses 11:825-871 (1997).

Nicholls, K.H. El Nino, ice cover, and Great lakes phosphorus; Implications for climate warming. Limnology and 

Oceanography 43:715-719 (1998).

World Meteorological Organization. WMO Sea-ice nomenclature, WMO/OMM/BM) – No. 259. TP. 145, 

Secretariat of the World Meteorological Organization, Geneva, Switzerland (1970).
16 

Figure 1a. Lake Bathymetry.

Figure 1b. Average February air temperatures (oC).
17

Figure 1c. Place names for the Great Lakes.
18 

Figure 2a. Combined Great Lakes 

inter-annual variations in the 

percent of depth range (≤ 20m) 

with ice at the ≥ 90% and with ice 

at the ≥ 10% ice concentration 

threshold values.

Figure 2b. Combined Great 

Lakes inter-annual variations in 

the percent of representative midlake depth range with ice at the ≥ 

90% and the ≥ 10% ice concentration threshold values.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90%

 Area of Ice 101 - 200 m

Great Lakes

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90%

 Area of Ice 0 - 20 m

Great Lakes
19

Figure 2d. Same as 2b but for 

Lake Superior.

Figure 2c.Same as 2a but for 

Lake Superior.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90%

Area of Ice for 20 m

Lake Superior

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90%

Area of Ice for 101- 200 m

Lake Superior
20 

Figure 2e. Same as 2a but for 

Lake Michigan.

Figure 2f. Same as 2b but for 

Lake Michigan.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 0 - 20 m

Lake Michigan

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 101 - 200 m

Lake Michigan
21

Figure 2g. Same as 2a but for 

Lake Huron.

Figure 2h. Same as 2b but for 

Lake Huron.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 0 - 20 m

Lake Huron

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 101 - 200 m

Lake Huron
22 

Figure 2i. Same as 2a but for 

Lake Erie.

Figure 2j. Same as 2b but for 

Lake Erie.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 0 - 20 m

Lake Erie

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 21 - 50 m

Lake Erie
23

Figure 2k. Same as 2a but for 

Lake Ontario.

Figure 2l. Same as 2b but for 

Lake Ontario.

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 0 - 20 m

Lake Ontario

0 

20 

40 

60 

80 

100 Percent of Area

1970 1980 1990 2000 

10% 90 %

Area of Ice 101 - 200 m

Lake Ontario
24 

Figure 3a. Thirty-winter average dates of first reported ice at the ≥ 90% threshold value.

16-Dec 

31-Dec 

15-Jan 

30-Jan 

14-Feb 

01-Mar 

1970 1980 1990 2000 

0-20 M 101-200 M

First Reported Ice 90%

Great Lakes

Figure 3b. Spatial 

averaged dates of 

first ice for the shore 

area (0-20 m depth 

range) and mid lake 

area (101-200 m 

depth range). The 

horizontal black lines 

are the 30-winter 

averages.
25

Figure 3b-1.Same as 3b but for Lake Superior. Figure 3b-2. Same as 3b but for Lake Michigan.

Figure 3b-3.Same as 3b but for Lake Huron.

Figure 3b-5. Same 

as 3b but for Lake 

Ontario.

Figure 3b-4. Same as 3b but for Lake Erie.

10-Dec 

20-Dec 

30-Dec 

09-Jan 

19-Jan 

29-Jan 

08-Feb 

18-Feb 

28-Feb 

1970 1980 1990 2000 

20 M 101-200 M

First Reported Ice 90%

Lake Superior

22-Dec 

01-Jan 

11-Jan 

21-Jan 

31-Jan 

10-Feb 

20-Feb 

02-Mar 

12-Mar 

1970 1980 1990 2000 

0-20 M 101-200 M

First Reported Ice 90%

Lake Michigan

12-Dec 

22-Dec 

01-Jan 

11-Jan 

21-Jan 

31-Jan 

10-Feb 

20-Feb 

02-Mar 

12-Mar 

1970 1980 1990 2000 

0-20 M 101-200 M

First Reported Ice 90%

Lake Huron

12-Dec 

22-Dec 

01-Jan 

11-Jan 

21-Jan 

31-Jan 

10-Feb 

20-Feb 

02-Mar 

12-Mar 

1970 1980 1990 2000 

0-20 M 21-50 M

First Reported Ice 90%

Lake Erie

12-Dec 

22-Dec 

01-Jan 

11-Jan 

21-Jan 

31-Jan 

10-Feb 

20-Feb 

02-Mar 

12-Mar 

1970 1980 1990 2000 

0-20 M 51-100 M

First Reported Ice 90%

Lake Ontario
26 

Figure 3c. Winter 1977 spatial distribution of dates of first reported ice at the ≥ 90% ice threshold.

Figure 3d.Thirty-winter composite minimum (earliest) dates of first reported ice at the ≥ 10% ice threshold.
27

Figure 3e. Winter 1998 spatial distribution of dates of first reported ice at the ≥ 90% ice threshold.

Figure 3f. Thirty-winter composite maximum (latest) dates of first reported ice at the ≥ 10% ice threshold.
28 

Figure 4a. Thirty-winter average dates of last reported ice at the ≥ 90% threshold value.

Figure 4b. Spatial 

averaged dates of last 

ice for the shore area 

(0-20 m depth range) 

and mid lake area (101-

200 m depth range). The 

horizontal black lines are 

the 30-winter averages.

15-Jan 

30-Jan 

14-Feb 

01-Mar 

16-Mar 

31-Mar 

15-Apr 

1970 1980 1990 2000 

0-20 M 101-200 M

Last Reported Ice 90%

Great Lakes
29

Figure 4b-2.Same as 4b but for Lake Michigan.

Figure 4b-5.Same as 4b but for Lake Ontario.

Figure 4b-4.Same as 4b but for Lake Erie.

Figure 4b-1.Same as 4b but for Lake Superior.

Figure 4b-3.Same as 4b but for Lake Huron.

12-Jan

27-Jan

11-Feb

26-Feb

13-Mar

28-Mar

12-Apr

27-Apr

1970 1980 1990 2000

20 M 101-200 M

Last Reported Ice 90%

Lake Superior

01-Jan

16-Jan

31-Jan

15-Feb

02-Mar

17-Mar

01-Apr

1970 1980 1990 2000

0-20 M 101-200 M

Last Reported Ice 90%

Lake Michigan

01-Feb

16-Feb

03-Mar

18-Mar

02-Apr

17-Apr

1970 1980 1990 2000

0-20 M 101-200 M

Last Reported Ice 90%

Lake Huron

08-Jan

23-Jan

07-Feb

22-Feb

09-Mar

24-Mar

08-Apr

1970 1980 1990 2000

0-20 M 21-50 M

Last Reported Ice 90%

Lake Erie

01-Jan

16-Jan

31-Jan

15-Feb

02-Mar

17-Mar

01-Apr

1970 1980 1990 2000

0-20 M 51-100 M

Last Reported Ice 90%

Lake Ontario
30 

Figure 4c. Winter 1994 spatial distribution pattern of dates last reported ice at the ≥ 90% ice threshold.

Figure 4d. Thirty-winter composite maximum (latest) dates of last reported ice at the ≥ 10% ice threshold.
31

Figure 4e. Winter 1998 spatial distribution pattern of dates last reported ice at the ≥ 90% ice threshold.

Figure 4f. Thirty-winter composite minimum (earliest) dates of last reported ice at the ≥ 10% ice threshold.
32 

Figure 5a. Thirty-winter average ice duration at the ≥ 90% threshold value.

Figure 5b. Spatial averaged ice 

duration for the shore area (0-

20 m depth range) and mid lake 

area (101-200 m depth range). 

The horizontal black lines are 

the 30-winter averages.

0 

20 

40 

60 

80 

100 Days

1970 1980 1990 2000 

0-20 M 101-200 M

Ice Duration for Ice 90%

Great Lakes
33

Figure 5b-1.Same as 5b but for Lake Superior.

Figure 5b-5.Same as 5b but for Lake Ontario.

Figure 5b-3.Same as 5b but for Lake Huron. Figure 5b-4.Same as 5b but for Lake Erie.

Figure 5b-2.Same as 5b but for Lake Michigan.

0 

20 

40 

60 

80 

100 

120 Days

1970 1980 1990 2000 

20 M 101-200 M

Ice Duration for Ice 90%

Lake Superior

0 

20 

40 

60 

80 

100 

120 Days

1970 1980 1990 2000 

0-20 M 101-200 M

Ice Duration for Ice 90%

Lake Michigan

0 

20 

40 

60 

80 

100 

120 Days

1970 1980 1990 2000 

0-20 M 101-200 M

Ice Duration for Ice 90%

Lake Huron

0 

20 

40 

60 

80 

100 

120 Days

1970 1980 1990 2000 

0-20 M 21-50 M

Ice Duration for Ice 90%

Lake Erie

0 

20 

40 

60 

80 

100 

120 Days

1970 1980 1990 2000 

0-20 M 51-100 M

Ice Duration for Ice 90%

Lake Ontario
34 

Figure 5c.Winter 1997 spatial distribution pattern of ice duration at the ≥ 90% threshold.

Figure 5d. Thirty-winter composite maximum ice duration at the ≥ 10% ice threshold. 
35

Figure 5e. Winter 1998 spatial distribution pattern of ice duration at the ≥ 90% threshold.

Figure 5f. Thirty-winter composite minimum ice duration at the ≥ 10% ice threshold.
36 

Table 1. Distribution of Ice Charts by Winter Season.

First Ice Chart Last Ice Chart

Winter No. Month Day % Ice Month Day % Ice

1973 16 12 20 10.5 4 6 2.1 

1974 18 12 31 5.5 5 2 1.5 

1975 17 1 2 1.6 4 24 4.0 

1976 18 12 23 10.0 4 20 1.5 

1977 21 12 16 17.5 5 4 0.8 

1978 20 12 21 3.6 5 3 1.5 

1979 23 12 18 2.8 5 14 2.9 

1980 16 1 2 6.0 4 16 3.1 

1981 16 12 24 9.3 4 15 2.6 

1982 22 12 21 0.9 5 17 0.1 

1983 20 12 21 0.5 5 3 0.3 

1984 22 12 20 8.2 5 3 0.1 

1985 19 12 22 0.7 4 27 0.5 

1986 20 12 14 3.4 4 23 0.3 

1987 15 12 27 1.8 4 5 2.2 

1988 16 1 3 2.6 4 17 1.4 

1989 82 12 14 3.2 5 8 0.2

1990 78 12 13 3.9 4 27 0.3 

1991 71 12 28 1.2 5 1 0.1 

1992 91 12 6 4.0 5 11 0.0

1993 82 12 14 0.3 5 5 0.2 

 1994 85 12 3 0.5 5 16 0.2 

1995 90 12 5 0.0 5 22 0.0 

1996 75 11 17 0.2 5 31 < 0.1

1997 49 11 26 0.3 5 13 0.1

1998 42 12 2 0.1 4 24 0.1

1999 36 12 15 0.1 5 4 0.1

2000 42 12 3 0.1 4 28 0.1

2001 43 12 1 0.1 5 3 0.0

2002 45 12 3 0.3 5 9 0.0

No. = number of ice charts for a given winter season.

% Ice = the lake averaged ice cover concentration.
37

Table 2.1 Great Lakes statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 21-Jan 29-Jan 08-Feb 17-Feb 21-Feb 05-Mar 01-Mar 02-Mar 02-Mar 01-Mar 43.7 31.8 22.5 14.0 9.0

1974 16-Jan 26-Jan 30-Jan 04-Feb 12-Feb 15-Mar 10-Mar 09-Mar 14-Mar 16-Mar 59.6 44.5 38.5 38.4 33.0

1975 29-Jan 03-Feb 08-Feb 08-Feb 07-Feb 13-Mar 08-Mar 06-Mar 24-Feb 23-Feb 43.4 33.7 26.8 16.9 16.8

1976 13-Jan 18-Jan 29-Jan 22-Feb 03-Mar 08-Mar 02-Mar 28-Feb 07-Mar 08-Mar 54.4 44.2 31.3 13.6 6.3

1977 26-Dec 01-Jan 14-Jan 22-Jan 24-Jan 20-Mar 19-Mar 16-Mar 18-Mar 19-Mar 85.5 77.6 61.9 55.7 54.9

1978 09-Jan 16-Jan 02-Feb 15-Feb 20-Feb 29-Mar 24-Mar 16-Mar 12-Mar 12-Mar 79.9 68.0 43.1 26.4 21.1

1979 11-Jan 18-Jan 30-Jan 03-Feb 07-Feb 23-Mar 20-Mar 16-Mar 25-Mar 01-Apr 72.6 62.6 46.4 51.2 53.7

1980 28-Jan 04-Feb 12-Feb 12-Feb 14-Feb 20-Mar 17-Mar 11-Mar 06-Mar 01-Mar 52.4 41.5 27.9 23.1 15.7

1981 04-Jan 08-Jan 16-Jan 28-Jan 03-Feb 10-Mar 04-Mar 24-Feb 02-Mar 07-Mar 66.1 56.1 39.9 34.3 33.9

1982 12-Jan 17-Jan 26-Jan 05-Feb 07-Feb 29-Mar 22-Mar 13-Mar 12-Mar 09-Mar 76.3 65.1 47.3 36.2 30.8

1983 26-Jan 28-Jan 02-Feb 08-Feb 07-Feb 25-Feb 24-Feb 17-Feb 16-Feb 03-Mar 31.6 28.9 15.9 9.1 24.2

1984 05-Jan 12-Jan 29-Jan 08-Feb 12-Feb 26-Mar 22-Mar 17-Mar 19-Mar 19-Mar 80.8 70.5 48.5 40.6 36.0

1985 12-Jan 21-Jan 01-Feb 04-Feb 08-Feb 16-Mar 12-Mar 07-Mar 07-Mar 07-Mar 64.4 50.1 34.8 32.9 28.5

1986 07-Jan 16-Jan 05-Feb 09-Feb 18-Feb 20-Mar 16-Mar 10-Mar 10-Mar 15-Mar 73.0 59.2 34.3 30.5 26.3

1987 29-Jan 05-Feb 07-Feb 04-Feb 16-Jan 02-Mar 27-Feb 19-Feb 06-Feb 21-Jan 33.6 23.1 12.7 3.4 6.5

1988 18-Jan 27-Jan 04-Feb 08-Feb 14-Feb 12-Mar 11-Mar 04-Mar 03-Mar 07-Mar 54.0 43.7 28.6 24.0 22.7

1989 18-Jan 01-Feb 11-Feb 15-Feb 24-Feb 27-Mar 23-Mar 25-Mar 25-Mar 26-Mar 68.6 51.7 42.9 38.6 30.3

1990 24-Dec 01-Jan 15-Jan 25-Jan 04-Feb 14-Mar 06-Mar 03-Mar 06-Mar 06-Mar 81.8 65.3 48.5 41.1 31.2

1991 20-Jan 28-Jan 31-Jan 29-Jan 01-Feb 12-Mar 07-Mar 07-Mar 14-Mar 12-Mar 51.5 39.3 36.0 44.2 40.0

1992 19-Jan 27-Jan 04-Feb 24-Feb 06-Mar 21-Mar 13-Mar 16-Mar 21-Mar 22-Mar 61.4 46.3 41.8 26.6 17.1

1993 21-Jan 03-Feb 13-Feb 20-Feb 24-Feb 25-Mar 19-Mar 15-Mar 16-Mar 20-Mar 64.3 44.7 31.5 25.3 24.9

1994 05-Jan 11-Jan 20-Jan 27-Jan 31-Jan 31-Mar 27-Mar 19-Mar 19-Mar 24-Mar 86.3 76.3 59.1 52.2 53.2

1995 28-Jan 06-Feb 17-Feb 22-Feb 25-Feb 13-Mar 10-Mar 04-Mar 01-Mar 07-Mar 45.5 33.4 15.3 7.8 10.7

1996 02-Jan 12-Jan 26-Jan 04-Feb 09-Feb 31-Mar 26-Mar 22-Mar 31-Mar 04-Apr 88.6 74.1 55.7 55.8 55.8

1997 13-Jan 20-Jan 03-Feb 13-Feb 23-Feb 19-Mar 13-Mar 14-Mar 25-Mar 27-Mar 66.3 52.7 40.0 41.2 32.7

1998 13-Jan 20-Jan 23-Jan 17-Jan 15-Jan 19-Feb 14-Feb 31-Jan 18-Jan 15-Jan 38.5 26.4 8.7 2.4 1.0

1999 16-Jan 23-Jan 12-Feb 21-Feb 19-Feb 07-Mar 05-Mar 27-Feb 28-Feb 23-Feb 51.4 42.3 16.0 7.6 5.7

2000 18-Jan 26-Jan 05-Feb 15-Feb 17-Feb 24-Feb 21-Feb 17-Feb 18-Feb 18-Feb 37.9 26.3 13.1 4.7 2.5

2001 06-Jan 12-Jan 01-Feb 26-Feb 28-Feb 15-Mar 10-Mar 02-Mar 16-Mar 14-Mar 68.7 57.4 29.5 19.0 14.6

2002 28-Jan 13-Feb 25-Feb 17-Feb 28-Feb 14-Mar 24-Mar 19-Mar 19-Feb 12-Mar 45.3 39.4 23.7 3.2 13.3

Maximum 29-Jan 13-Feb 25-Feb 26-Feb 06-Mar 31-Mar 27-Mar 25-Mar 31-Mar 04-Apr 88.6 77.6 61.9 55.8 55.8

Minimum 24-Dec 01-Jan 14-Jan 17-Jan 15-Jan 19-Feb 14-Feb 31-Jan 18-Jan 15-Jan 31.6 23.1 8.7 2.4 1.0

Average 14-Jan 22-Jan 02-Feb 09-Feb 13-Feb 15-Mar 11-Mar 07-Mar 07-Mar 09-Mar 60.9 49.2 34.1 27.3 25.1

Median 14-Jan 22-Jan 02-Feb 08-Feb 13-Feb 15-Mar 11-Mar 08-Mar 09-Mar 10-Mar 62.8 45.5 34.6 26.5 24.6

25% of pdf 08-Jan 16-Jan 29-Jan 04-Feb 07-Feb 10-Mar 06-Mar 02-Mar 01-Mar 04-Mar 46.9 39.3 24.5 13.7 13.6

75% of pdf 21-Jan 29-Jan 08-Feb 16-Feb 23-Feb 23-Mar 20-Mar 16-Mar 17-Mar 19-Mar 72.9 61.8 43.0 40.1 33.0

pdf = probability density function of the cumulative frequency distribution.
38 

Table 2.2. Lake Superior statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 12-Jan 23-Jan 02-Feb 18-Feb 21-Feb 13-Mar 09-Mar 08-Mar 05-Mar 01-Mar 61.8 46.3 34.6 15.2 8.5

1974 06-Jan 12-Jan 20-Jan 03-Feb 12-Feb 12-Apr 04-Apr 24-Mar 18-Mar 17-Mar 96.5 82.4 63.9 43.6 34.2

1975 18-Jan 28-Jan 04-Feb 08-Feb 05-Feb 01-Apr 18-Mar 08-Mar 22-Feb 25-Feb 73.9 50.0 33.5 14.4 20.7

1976 09-Jan 20-Jan 05-Feb 23-Feb 05-Mar 27-Mar 16-Mar 09-Mar 09-Mar 12-Mar 77.2 55.8 32.9 14.8 7.9

1977 23-Dec 27-Dec 02-Jan 15-Jan 24-Jan 09-Apr 04-Apr 28-Mar 20-Mar 21-Mar 108.8 100.1 85.4 65.4 56.9

1978 04-Jan 15-Jan 31-Jan 15-Feb 20-Feb 06-Apr 25-Mar 19-Mar 14-Mar 13-Mar 92.6 70.2 47.4 28.5 22.2

1979 05-Jan 12-Jan 18-Jan 28-Jan 06-Feb 23-Apr 19-Apr 11-Apr 08-Apr 03-Apr 108.4 97.8 83.9 71.3 56.5

1980 20-Jan 30-Jan 08-Feb 11-Feb 13-Feb 29-Mar 20-Mar 14-Mar 08-Mar 02-Mar 69.1 49.6 34.7 26.5 17.4

1981 05-Jan 11-Jan 17-Jan 27-Jan 02-Feb 30-Mar 22-Mar 16-Mar 10-Mar 08-Mar 84.9 71.5 59.4 43.5 35.1

1982 06-Jan 13-Jan 21-Jan 02-Feb 09-Feb 12-Apr 29-Mar 21-Mar 17-Mar 11-Mar 96.9 76.0 59.9 45.0 31.6

1983 15-Jan 26-Jan 01-Feb 07-Feb 08-Feb 12-Mar 22-Feb 16-Feb 14-Feb 03-Mar 57.1 28.5 16.0 7.7 23.9

1984 31-Dec 10-Jan 21-Jan 06-Feb 14-Feb 10-Apr 05-Apr 28-Mar 21-Mar 20-Mar 101.1 86.0 66.6 44.2 34.8

1985 01-Jan 07-Jan 17-Jan 01-Feb 10-Feb 30-Mar 21-Mar 16-Mar 11-Mar 08-Mar 88.6 73.8 59.2 39.3 27.4

1986 05-Jan 15-Jan 26-Jan 07-Feb 20-Feb 01-Apr 25-Mar 22-Mar 18-Mar 16-Mar 87.0 70.5 56.1 40.4 24.9

1987 20-Jan 28-Jan 30-Jan 31-Jan 19-Jan 04-Mar 14-Feb 08-Feb 02-Feb 19-Jan 44.0 18.4 9.9 2.3 1.0

1988 15-Jan 21-Jan 28-Jan 09-Feb 13-Feb 22-Mar 14-Mar 07-Mar 06-Mar 08-Mar 66.5 52.6 39.1 25.8 23.4

1989 01-Jan 10-Jan 22-Jan 11-Feb 25-Feb 12-Apr 07-Apr 02-Apr 27-Mar 27-Mar 102.0 88.2 70.6 45.0 31.0

1990 19-Dec 24-Dec 01-Jan 24-Jan 04-Feb 01-Apr 23-Mar 14-Mar 09-Mar 06-Mar 104.4 91.1 73.1 45.1 31.0

1991 07-Jan 15-Jan 21-Jan 28-Jan 03-Feb 03-Apr 25-Mar 16-Mar 14-Mar 12-Mar 86.8 69.9 55.3 45.9 37.3

1992 27-Dec 12-Jan 02-Feb 26-Feb 07-Mar 04-Apr 29-Mar 24-Mar 24-Mar 22-Mar 100.1 77.0 51.3 27.3 16.5

1993 10-Jan 22-Jan 06-Feb 20-Feb 24-Feb 03-Apr 22-Mar 19-Mar 19-Mar 21-Mar 84.1 60.6 41.4 28.1 26.1

1994 30-Dec 07-Jan 15-Jan 22-Jan 28-Jan 14-Apr 09-Apr 03-Apr 29-Mar 28-Mar 106.7 92.4 79.1 67.0 59.8

1995 23-Jan 06-Feb 18-Feb 22-Feb 25-Feb 26-Mar 14-Mar 05-Mar 28-Feb 06-Mar 63.5 36.9 16.3 7.0 10.1

1996 01-Jan 15-Jan 25-Jan 02-Feb 09-Feb 30-Apr 23-Apr 17-Apr 10-Apr 06-Apr 119.9 99.2 82.5 67.3 57.7

1997 06-Jan 19-Jan 31-Jan 14-Feb 25-Feb 13-Apr 07-Apr 03-Apr 31-Mar 27-Mar 98.5 79.0 62.8 46.4 31.3

1998 06-Jan 14-Jan 15-Jan 15-Jan 15-Jan 18-Feb 26-Jan 19-Jan 15-Jan 15-Jan 43.1 13.0 5.0 1.4 1.0

1999 11-Jan 22-Jan 11-Feb 23-Feb 26-Feb 15-Mar 27-Feb 01-Mar 01-Mar 28-Feb 63.6 37.4 19.8 7.5 3.2

2000 15-Jan 29-Jan 09-Feb 16-Feb 15-Feb 04-Mar 22-Feb 19-Feb 19-Feb 17-Feb 49.7 24.7 10.7 4.0 3.6

2001 14-Jan 29-Jan 13-Feb 27-Feb 01-Mar 04-Apr 24-Mar 18-Mar 16-Mar 15-Mar 80.2 55.5 34.6 17.8 15.2

2002 27-Jan 19-Feb 26-Feb 24-Feb 14-Feb 31-Mar 23-Mar 25-Mar 07-Mar 23-Feb 64.3 33.1 28.3 12.0 9.6

Maximum 27-Jan 19-Feb 26-Feb 27-Feb 07-Mar 30-Apr 23-Apr 17-Apr 10-Apr 06-Apr 119.9 100.1 85.4 71.3 59.8

Minimum 19-Dec 24-Dec 01-Jan 15-Jan 15-Jan 18-Feb 26-Jan 19-Jan 15-Jan 15-Jan 43.1 13.0 5.0 1.4 1.0

Average 08-Jan 18-Jan 28-Jan 08-Feb 13-Feb 30-Mar 21-Mar 15-Mar 10-Mar 09-Mar 82.7 62.9 47.1 31.7 25.3

Median 06-Jan 15-Jan 29-Jan 08-Feb 13-Feb 01-Apr 23-Mar 17-Mar 13-Mar 11-Mar 85.9 70.1 49.4 28.3 24.4

25% of pdf 02-Jan 12-Jan 20-Jan 31-Jan 05-Feb 26-Mar 14-Mar 08-Mar 05-Mar 02-Mar 64.9 47.1 33.1 14.5 11.4

75% of pdf 15-Jan 25-Jan 05-Feb 18-Feb 24-Feb 10-Apr 02-Apr 25-Mar 20-Mar 21-Mar 99.7 81.6 63.6 45.0 33.6

pdf = probability density function of the cumulative frequency distribution.
39

Table 2.3. Lake Michigan statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 18-Jan 20-Jan 28-Jan 29-Jan NA 01-Mar 19-Feb 20-Feb 05-Feb NA 42.9 30.8 30.8 8.8 NA

1974 20-Jan 25-Jan 07-Feb 13-Feb NA 13-Mar 01-Mar 24-Feb 22-Feb NA 53.5 35.7 35.7 10.5 NA

1975 23-Jan 27-Jan 06-Feb 12-Feb NA 10-Mar 06-Mar 15-Feb 12-Feb NA 46.9 38.5 38.5 1.0 NA

1976 08-Jan 18-Jan 30-Jan 19-Jan NA 04-Mar 27-Feb 10-Feb 24-Jan NA 55.8 41.4 41.4 6.1 NA

1977 26-Dec 30-Dec 18-Jan 30-Jan 06-Feb 13-Mar 11-Mar 05-Mar 10-Mar 08-Mar 79.1 72.1 72.1 39.3 31.0

1978 10-Jan 19-Jan 09-Feb 20-Feb 02-Mar 18-Mar 16-Mar 08-Mar 05-Mar 07-Mar 68.5 56.2 56.2 14.5 5.6

1979 11-Jan 18-Jan 03-Feb 13-Feb 15-Feb 23-Mar 17-Mar 08-Mar 09-Mar 12-Mar 72.3 59.7 59.7 24.9 25.8

1980 27-Jan 06-Feb 18-Feb 15-Feb NA 16-Mar 09-Mar 27-Feb 15-Feb NA 48.1 32.2 32.2 1.6 NA

1981 03-Jan 09-Jan 16-Jan 29-Jan 10-Feb 05-Mar 24-Feb 09-Feb 09-Feb 10-Feb 61.8 47.6 47.6 11.6 1.0

1982 11-Jan 15-Jan 25-Jan 07-Feb 09-Feb 15-Mar 07-Mar 26-Feb 28-Feb 15-Feb 63.2 51.2 51.2 21.6 6.9

1983 26-Jan 29-Jan 10-Feb 12-Feb NA 07-Mar 26-Feb 17-Feb 14-Feb NA 40.9 28.3 28.3 2.7 NA

1984 10-Jan 19-Jan 01-Feb 09-Feb NA 08-Mar 28-Feb 17-Feb 26-Feb NA 57.3 41.8 41.8 18.2 NA

1985 15-Jan 27-Jan 13-Feb 22-Feb NA 18-Mar 12-Mar 03-Mar 02-Mar NA 63.2 44.6 44.6 9.4 NA

1986 20-Jan 29-Jan 05-Feb 07-Feb 21-Feb 14-Mar 07-Mar 20-Feb 15-Feb 22-Feb 54.1 38.8 38.8 8.6 1.8

1987 22-Jan 31-Jan 14-Feb 19-Feb NA 02-Mar 03-Mar 20-Feb 20-Feb NA 39.7 31.3 31.3 1.2 NA

1988 15-Jan 20-Jan 19-Jan 15-Jan NA 06-Mar 25-Feb 05-Feb 21-Jan NA 51.5 37.9 37.9 6.8 NA

1989 23-Jan 02-Feb 20-Feb 06-Mar 18-Mar 24-Mar 20-Mar 16-Mar 16-Mar 18-Mar 61.3 47.0 47.0 10.3 1.0

1990 26-Dec 04-Jan 18-Jan 02-Feb NA 12-Mar 02-Mar 20-Feb 06-Mar NA 77.9 58.5 58.5 32.8 NA

1991 18-Jan 18-Jan 06-Feb 16-Feb NA 10-Mar 08-Mar 02-Mar 22-Feb NA 52.1 49.7 49.7 6.8 NA

1992 19-Jan 26-Jan 29-Jan 02-Feb 02-Feb 06-Mar 24-Feb 11-Feb 06-Feb 02-Feb 47.1 30.1 30.1 5.0 1.0

1993 23-Jan 01-Feb 14-Feb 19-Feb NA 12-Mar 03-Mar 26-Feb 24-Feb NA 48.6 31.0 31.0 5.6 NA

1994 04-Jan 14-Jan 28-Jan 06-Feb 20-Feb 23-Mar 16-Mar 07-Mar 03-Mar 06-Mar 78.5 62.3 62.3 26.5 14.2

1995 29-Jan 08-Feb 16-Feb 12-Feb NA 10-Mar 03-Mar 22-Feb 12-Feb NA 40.6 24.2 24.2 1.0 NA

1996 04-Jan 16-Jan 02-Feb 10-Feb 05-Mar 27-Mar 17-Mar 02-Mar 03-Mar 07-Mar 83.4 61.3 61.3 22.1 2.2

1997 07-Jan 18-Jan 28-Jan 06-Feb 13-Feb 09-Mar 02-Mar 18-Feb 14-Feb 13-Feb 61.3 43.9 43.9 9.0 1.0

1998 12-Jan 21-Jan 07-Feb NA NA 22-Feb 20-Feb 07-Feb NA NA 41.5 31.2 31.2 NA NA

1999 09-Jan 14-Jan 25-Jan 14-Jan NA 27-Feb 26-Feb 26-Jan 14-Jan NA 49.8 44.2 44.2 1.0 NA

2000 19-Jan 23-Jan 02-Feb 17-Feb NA 20-Feb 23-Feb 13-Feb 17-Feb NA 33.8 32.1 32.1 1.0 NA

2001 01-Jan 07-Jan 14-Jan 10-Jan NA 11-Mar 27-Feb 23-Jan 10-Jan NA 70.5 51.8 51.8 1.0 NA

2002 03-Feb 09-Feb 17-Feb NA NA 22-Mar 22-Mar 20-Feb NA NA 47.9 42.4 42.4 NA NA

Maximum 03-Feb 09-Feb 20-Feb 06-Mar 18-Mar 27-Mar 22-Mar 16-Mar 16-Mar 18-Mar 83.4 72.1 72.1 39.3 31.0

Minimum 26-Dec 30-Dec 14-Jan 10-Jan 02-Feb 20-Feb 19-Feb 23-Jan 10-Jan 02-Feb 33.8 24.2 24.2 0.0 1.0

Average 14-Jan 21-Jan 02-Feb 05-Feb 19-Feb 11-Mar 05-Mar 20-Feb 17-Feb 26-Feb 56.4 43.3 43.3 10.3 8.3

Median 15-Jan 20-Jan 02-Feb 09-Feb 15-Feb 10-Mar 03-Mar 20-Feb 18-Feb 06-Mar 53.8 42.1 42.1 8.7 2.2

25% of pdf 08-Jan 16-Jan 28-Jan 30-Jan 09-Feb 06-Mar 26-Feb 13-Feb 11-Feb 14-Feb 47.3 32.1 32.1 1.3 1.0

75% of pdf 22-Jan 28-Jan 09-Feb 14-Feb 26-Feb 15-Mar 11-Mar 01-Mar 02-Mar 07-Mar 63.2 50.8 50.8 13.8 10.6

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
40 

Table 2.4. Lake Huron statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 08-Jan 26-Jan 14-Feb 20-Feb 19-Feb 10-Mar 06-Mar 02-Mar 02-Mar 19-Feb 61.4 40.4 17.2 11.2 1.0

1974 12-Jan 22-Jan 06-Feb 20-Feb 27-Feb 22-Mar 14-Mar 06-Mar 01-Mar 27-Feb 70.0 51.8 28.4 9.6 1.0

1975 25-Jan 02-Feb 16-Feb 03-Feb 05-Feb 23-Mar 13-Mar 08-Mar 11-Feb 05-Feb 58.1 39.9 21.7 8.6 1.0

1976 07-Jan 13-Jan 25-Jan 14-Feb 02-Mar 14-Mar 05-Mar 28-Feb 25-Feb 02-Mar 66.7 52.0 34.8 11.4 1.0

1977 23-Dec 02-Jan 15-Jan 01-Feb 09-Feb 26-Mar 21-Mar 20-Mar 21-Mar 22-Mar 95.2 79.1 64.7 49.0 41.7

1978 03-Jan 15-Jan 27-Jan 11-Feb 10-Feb 02-Apr 27-Mar 20-Mar 17-Mar 14-Mar 90.0 71.9 52.5 35.7 32.2

1979 08-Jan 19-Jan 31-Jan 09-Feb 11-Feb 25-Mar 17-Mar 14-Mar 11-Mar 07-Mar 77.6 57.1 43.5 30.7 24.5

1980 25-Jan 05-Feb 14-Feb 20-Feb 05-Feb 25-Mar 22-Mar 14-Mar 04-Mar 05-Feb 60.4 45.6 28.9 12.9 1.0

1981 02-Jan 07-Jan 17-Jan 30-Jan 03-Feb 16-Mar 07-Mar 27-Feb 21-Feb 18-Feb 74.0 59.2 42.3 23.0 16.3

1982 11-Jan 19-Jan 28-Jan 11-Feb 23-Feb 08-Apr 30-Mar 21-Mar 09-Mar 08-Mar 87.6 71.4 53.6 26.0 13.4

1983 24-Jan 27-Jan 30-Jan 30-Jan NA 01-Mar 24-Feb 15-Feb 04-Feb NA 36.2 28.2 17.0 6.0 NA

1984 31-Dec 12-Jan 01-Feb 21-Feb 07-Feb 02-Apr 27-Mar 24-Mar 16-Mar 07-Mar 93.4 75.9 51.5 23.6 29.7

1985 08-Jan 19-Jan 05-Feb 14-Feb 13-Feb 22-Mar 12-Mar 06-Mar 24-Feb 22-Feb 74.0 53.5 29.9 10.8 9.3

1986 01-Jan 18-Jan 08-Feb 14-Feb 23-Feb 23-Mar 15-Mar 14-Mar 03-Mar 28-Feb 81.5 56.8 35.2 18.3 5.7

1987 28-Jan 03-Feb 09-Feb 04-Feb NA 09-Mar 04-Mar 23-Feb 12-Feb NA 40.3 29.6 15.4 8.8 NA

1988 17-Jan 01-Feb 16-Feb 24-Feb 06-Mar 19-Mar 16-Mar 12-Mar 06-Mar 06-Mar 62.7 44.4 24.7 11.5 1.0

1989 10-Jan 30-Jan 20-Feb 05-Mar 09-Mar 03-Apr 28-Mar 24-Mar 20-Mar 15-Mar 83.5 58.2 33.0 16.0 7.7

1990 21-Dec 01-Jan 23-Jan 12-Feb NA 18-Mar 08-Mar 06-Mar 02-Mar NA 88.8 67.4 42.6 18.1 NA

1991 13-Jan 21-Jan 07-Feb 13-Feb NA 16-Mar 04-Mar 26-Feb 26-Feb NA 62.3 43.4 20.3 13.5 NA

1992 14-Jan 23-Jan 08-Feb 10-Feb NA 04-Apr 25-Mar 26-Mar 22-Mar NA 80.8 62.2 47.1 41.6 NA

1993 14-Jan 28-Jan 16-Feb 23-Feb 27-Feb 03-Apr 27-Mar 19-Mar 09-Mar 27-Feb 80.3 58.2 31.9 15.7 1.0

1994 02-Jan 08-Jan 16-Jan 27-Jan 28-Jan 07-Apr 03-Apr 28-Mar 25-Mar 24-Mar 96.1 85.7 71.7 57.2 55.6

1995 21-Jan 05-Feb 19-Feb 02-Mar NA 20-Mar 10-Mar 04-Mar 09-Mar NA 58.2 33.8 13.1 8.0 NA

1996 26-Dec 08-Jan 24-Jan 05-Feb 12-Feb 05-Apr 29-Mar 24-Mar 19-Mar 17-Mar 101.8 80.9 59.6 43.4 34.7

1997 10-Jan 24-Jan 07-Feb 10-Feb 18-Feb 29-Mar 19-Mar 12-Mar 28-Feb 24-Feb 79.0 55.0 34.4 19.1 6.5

1998 14-Jan 23-Jan 01-Feb 04-Feb NA 25-Feb 19-Feb 13-Feb 08-Feb NA 43.0 28.6 13.3 4.3 NA

1999 13-Jan 28-Jan 18-Feb 26-Feb NA 12-Mar 10-Mar 05-Mar 08-Mar NA 58.4 42.6 15.8 11.4 NA

2000 13-Jan 24-Jan 03-Feb 08-Feb NA 01-Mar 21-Feb 16-Feb 11-Feb NA 47.6 28.7 14.2 3.6 NA

2001 31-Dec 16-Jan 05-Feb 27-Feb NA 24-Mar 11-Mar 06-Mar 19-Mar NA 83.2 55.7 29.4 21.8 NA

2002 01-Feb 17-Feb 01-Mar NA NA 27-Mar 26-Mar 29-Mar NA NA 55.0 37.7 28.9 NA NA

Maximum 01-Feb 17-Feb 01-Mar 05-Mar 09-Mar 08-Apr 03-Apr 29-Mar 25-Mar 24-Mar 101.8 85.7 71.7 57.2 55.6

Minimum 21-Dec 01-Jan 15-Jan 27-Jan 28-Jan 25-Feb 19-Feb 13-Feb 04-Feb 05-Feb 36.2 28.2 13.1 3.6 0.0

Average 10-Jan 22-Jan 05-Feb 12-Feb 16-Feb 22-Mar 15-Mar 10-Mar 04-Mar 02-Mar 71.6 53.2 33.9 19.7 13.5

Median 11-Jan 22-Jan 06-Feb 12-Feb 13-Feb 23-Mar 14-Mar 10-Mar 04-Mar 02-Mar 74.0 54.3 30.9 15.7 7.7

25% of pdf 03-Jan 15-Jan 28-Jan 04-Feb 08-Feb 16-Mar 07-Mar 03-Mar 25-Feb 23-Feb 58.9 41.0 20.7 10.8 1.0

75% of pdf 14-Jan 28-Jan 14-Feb 20-Feb 24-Feb 01-Apr 26-Mar 20-Mar 16-Mar 11-Mar 83.4 61.5 43.3 23.6 24.5

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
41

Table 2.5. Lake Erie statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 03-Feb 14-Feb 22-Feb NA NA 27-Feb 28-Feb 27-Feb NA NA 25.1 15.2 6.4 NA NA

1974 19-Jan 07-Feb 23-Jan NA NA 24-Feb 02-Mar 12-Mar NA NA 36.4 23.8 48.6 NA NA

1975 10-Feb 14-Feb 26-Feb NA NA 28-Feb 02-Mar 26-Feb NA NA 19.1 17.2 1.0 NA NA

1976 14-Jan 22-Jan 25-Jan NA NA 19-Feb 23-Feb 02-Mar NA NA 36.7 33.2 36.1 NA NA

1977 26-Dec 01-Jan 04-Jan NA NA 11-Mar 17-Mar 22-Mar NA NA 76.9 75.8 77.8 NA NA

1978 05-Jan 11-Jan 15-Jan NA NA 28-Mar 01-Apr 03-Apr NA NA 83.6 81.2 79.1 NA NA

1979 09-Jan 13-Jan 19-Jan NA NA 12-Mar 20-Mar 21-Mar NA NA 62.9 67.2 62.3 NA NA

1980 30-Jan 05-Feb 07-Feb NA NA 14-Mar 17-Mar 23-Mar NA NA 44.0 40.9 45.1 NA NA

1981 02-Jan 06-Jan 06-Jan NA NA 28-Feb 06-Mar 27-Mar NA NA 57.6 60.4 81.6 NA NA

1982 14-Jan 17-Jan 17-Jan NA NA 25-Mar 30-Mar 11-Apr NA NA 71.2 73.9 85.1 NA NA

1983 01-Feb 13-Feb NA NA NA 13-Feb 13-Feb NA NA NA 12.7 1.0 NA NA NA

1984 31-Dec 03-Jan 10-Jan NA NA 30-Mar 01-Apr 08-Apr NA NA 89.8 88.5 89.1 NA NA

1985 16-Jan 26-Jan 01-Feb NA NA 08-Mar 13-Mar 28-Mar NA NA 52.2 46.7 56.4 NA NA

1986 27-Dec 27-Dec 27-Dec NA NA 17-Mar 23-Mar 29-Mar NA NA 82.5 87.1 93.4 NA NA

1987 01-Feb 13-Feb 18-Feb NA NA 23-Feb 24-Feb 27-Feb NA NA 22.3 12.5 9.4 NA NA

1988 18-Jan 31-Jan 07-Feb NA NA 06-Mar 15-Mar 30-Mar NA NA 48.6 44.1 52.1 NA NA

1989 28-Jan 10-Feb 13-Feb NA NA 12-Mar 10-Mar 09-Mar NA NA 43.9 29.0 24.2 NA NA

1990 23-Dec 04-Jan 03-Jan NA NA 01-Mar 04-Mar 12-Mar NA NA 69.9 60.0 68.9 NA NA

1991 10-Feb 27-Feb 27-Feb NA NA 25-Feb 01-Mar 28-Feb NA NA 15.6 3.4 2.5 NA NA

1992 27-Jan 08-Feb 10-Feb NA NA 04-Mar 04-Mar 03-Mar NA NA 37.2 25.1 22.5 NA NA

1993 27-Jan 16-Feb 18-Feb NA NA 24-Mar 22-Mar 21-Mar NA NA 57.2 34.5 31.8 NA NA

1994 06-Jan 14-Jan 15-Jan NA NA 22-Mar 29-Mar 09-Apr NA NA 75.6 75.8 84.9 NA NA

1995 30-Jan 08-Feb 11-Feb NA NA 08-Mar 15-Mar 17-Mar NA NA 38.5 36.4 34.7 NA NA

1996 29-Dec 09-Jan 13-Jan NA NA 18-Mar 25-Mar 26-Mar NA NA 81.1 76.4 72.3 NA NA

1997 13-Jan 17-Jan 26-Jan NA NA 24-Feb 02-Mar 20-Mar NA NA 43.3 45.3 53.9 NA NA

1998 20-Jan 15-Jan NA NA NA 28-Jan 15-Jan NA NA NA 9.0 1.0 NA NA NA

1999 18-Jan 25-Jan 08-Mar NA NA 06-Mar 08-Mar 09-Mar NA NA 47.8 42.9 1.7 NA NA

2000 21-Jan 29-Jan 31-Jan NA NA 20-Feb 20-Feb 04-Feb NA NA 30.7 23.1 4.9 NA NA

2001 26-Dec 04-Jan 19-Jan NA NA 26-Feb 12-Mar 07-Apr NA NA 63.4 68.0 79.1 NA NA

2002 12-Jan 10-Feb NA NA NA 23-Jan 10-Feb NA NA NA 12.3 1.0 NA NA NA

Maximum 10-Feb 27-Feb 08-Mar NA NA 30-Mar 01-Apr 11-Apr NA NA 89.8 88.5 93.4 NA NA

Minimum 23-Dec 27-Dec 27-Dec NA NA 23-Jan 15-Jan 04-Feb NA NA 9.0 1.0 1.0 NA NA

Average 16-Jan 25-Jan 29-Jan NA NA 04-Mar 08-Mar 18-Mar NA NA 48.2 43.0 48.3 NA NA

Median 17-Jan 26-Jan 27-Jan NA NA 05-Mar 09-Mar 21-Mar NA NA 45.9 41.9 52.1 NA NA

25% of pdf 05-Jan 12-Jan 15-Jan NA NA 24-Feb 01-Mar 06-Mar NA NA 32.1 23.3 23.4 NA NA

75% of pdf 28-Jan 09-Feb 12-Feb NA NA 13-Mar 19-Mar 28-Mar NA NA 68.3 67.8 78.5 NA NA

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
42 

Table 2.6. Lake Ontario statistics for discrete depth ranges for ice cover concentration ≥ 90%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 26-Jan 04-Feb 18-Feb 19-Feb NA 26-Feb 23-Feb 20-Feb 19-Feb NA 32.2 20.3 3.0 1.0 NA

1974 17-Jan 31-Jan 16-Jan 09-Jan NA 25-Feb 16-Feb 16-Jan 09-Jan NA 39.7 16.8 1.0 1.0 NA

1975 31-Jan 11-Feb 12-Feb NA NA 27-Feb 12-Feb 12-Feb NA NA 27.2 1.8 1.0 NA NA

1976 19-Jan 01-Feb 28-Jan 01-Feb NA 09-Mar 20-Feb 02-Feb 02-Feb NA 50.2 20.0 5.6 1.6 NA

1977 07-Jan 13-Jan 21-Jan 03-Feb 08-Feb 11-Mar 09-Mar 28-Feb 27-Feb 22-Feb 63.4 55.7 39.0 25.0 15.4

1978 16-Jan 26-Jan 16-Feb 18-Feb 14-Feb 18-Mar 11-Mar 06-Mar 26-Feb 17-Feb 61.9 44.7 18.9 8.5 4.6

1979 22-Jan 31-Jan 08-Feb 12-Feb 11-Feb 01-Mar 21-Feb 15-Feb 15-Feb 15-Feb 38.7 22.2 8.4 4.8 5.3

1980 05-Feb 14-Feb 13-Feb 12-Feb 12-Feb 14-Mar 01-Mar 21-Feb 18-Feb 12-Feb 37.5 16.2 9.0 7.2 1.0

1981 05-Jan 06-Jan 07-Jan 14-Jan 11-Jan 05-Feb 29-Jan 12-Jan 14-Jan 11-Jan 32.1 24.5 6.0 1.2 1.0

1982 23-Jan 23-Jan 25-Jan 29-Jan 04-Mar 09-Mar 06-Mar 16-Feb 20-Feb 08-Mar 46.4 42.6 23.5 23.9 4.6

1983 09-Feb 11-Feb 09-Feb NA NA 17-Feb 13-Feb 12-Feb NA NA 9.5 2.6 4.0 NA NA

1984 10-Jan 15-Jan 24-Jan 09-Feb NA 07-Mar 09-Mar 20-Feb 14-Feb NA 56.2 54.4 28.4 6.6 NA

1985 18-Jan 23-Jan 02-Feb 07-Feb 08-Feb 26-Feb 15-Feb 11-Feb 18-Feb 20-Feb 39.9 24.1 9.8 11.3 13.7

1986 23-Jan 05-Feb 16-Feb 21-Feb 28-Feb 10-Mar 07-Mar 05-Mar 03-Mar 28-Feb 46.9 31.0 18.5 11.9 1.0

1987 12-Feb 13-Feb NA NA NA 03-Mar 15-Feb NA NA NA 20.2 3.2 NA NA NA

1988 19-Jan 26-Jan 14-Feb NA NA 14-Mar 05-Mar 14-Feb NA NA 54.9 39.0 1.0 NA NA

1989 14-Feb 26-Feb 11-Mar NA NA 22-Mar 16-Mar 11-Mar NA NA 36.6 18.6 1.0 NA NA

1990 27-Dec 29-Dec 03-Jan 25-Dec 23-Dec 25-Feb 14-Feb 30-Jan 06-Jan 23-Dec 61.7 49.1 27.1 14.2 1.0

1991 17-Jan 29-Jan 25-Feb NA NA 05-Mar 21-Feb 25-Feb NA NA 48.4 24.2 1.0 NA NA

1992 26-Jan 03-Feb 13-Feb 15-Feb 15-Feb 16-Mar 08-Mar 15-Feb 15-Feb 15-Feb 49.1 33.8 3.0 1.0 1.0

1993 02-Feb 14-Feb 21-Feb 25-Feb NA 16-Mar 03-Mar 27-Feb 26-Feb NA 42.7 18.1 7.2 2.3 NA

1994 11-Jan 15-Jan 26-Jan 03-Feb 10-Feb 13-Mar 07-Mar 21-Feb 19-Feb 01-Mar 61.6 51.8 27.1 17.7 19.5

1995 06-Feb 09-Feb 09-Feb NA NA 06-Mar 24-Feb 12-Feb NA NA 29.3 16.0 3.5 NA NA

1996 17-Jan 17-Jan 19-Jan 03-Feb NA 27-Feb 16-Feb 06-Feb 09-Feb NA 42.3 31.4 18.6 6.3 NA

1997 22-Jan 27-Jan 10-Feb NA NA 16-Mar 19-Feb 10-Feb NA NA 53.6 24.6 1.0 NA NA

1998 24-Jan 05-Feb NA NA NA 09-Feb 08-Feb NA NA NA 17.6 3.9 NA NA NA

1999 18-Jan 03-Feb 29-Jan 21-Jan NA 23-Feb 14-Feb 16-Feb 18-Feb NA 37.0 12.1 19.1 29.0 NA

2000 21-Jan 31-Jan 02-Feb 31-Jan NA 18-Feb 11-Feb 02-Feb 31-Jan NA 28.9 12.1 1.0 1.0 NA

2001 10-Jan 22-Jan 19-Jan NA NA 28-Feb 17-Feb 28-Jan NA NA 50.6 26.8 10.2 NA NA

2002 18-Jan NA NA NA NA 23-Feb NA NA NA NA 37.4 NA NA NA NA

Maximum 14-Feb 26-Feb 11-Mar 25-Feb 04-Mar 22-Mar 16-Mar 11-Mar 03-Mar 08-Mar 63.4 55.7 39.0 29.0 19.5

Minimum 27-Dec 29-Dec 03-Jan 25-Dec 23-Dec 05-Feb 29-Jan 12-Jan 06-Jan 23-Dec 9.5 1.8 1.0 1.0 1.0

Average 22-Jan 29-Jan 04-Feb 03-Feb 07-Feb 03-Mar 23-Feb 14-Feb 12-Feb 13-Feb 41.8 25.6 11.0 9.2 6.2

Median 20-Jan 31-Jan 08-Feb 03-Feb 11-Feb 04-Mar 21-Feb 15-Feb 18-Feb 19-Feb 41.1 24.1 7.2 6.6 4.6

25% of pdf 17-Jan 23-Jan 24-Jan 30-Jan 08-Feb 25-Feb 15-Feb 08-Feb 10-Feb 14-Feb 33.3 16.2 2.0 1.4 1.0

75% of pdf 26-Jan 05-Feb 13-Feb 13-Feb 14-Feb 12-Mar 06-Mar 21-Feb 20-Feb 28-Feb 50.5 33.8 18.8 13.1 9.5

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
43

Table 3.1 Great Lakes statistics for discrete depth ranges for ice cover concentration≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days)

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 05-Jan 16-Jan 27-Jan 04-Feb 12-Feb 08-Mar 06-Mar 05-Mar 02-Mar 03-Mar 62.9 49.5 37.5 27.1 20.2

1974 11-Jan 20-Jan 29-Jan 06-Feb 16-Feb 22-Mar 17-Mar 17-Mar 28-Mar 31-Mar 71.0 56.4 47.4 50.9 43.9

1975 20-Jan 29-Jan 03-Feb 08-Feb 09-Feb 24-Mar 15-Mar 08-Mar 28-Feb 20-Feb 63.6 46.1 33.5 20.7 12.3

1976 06-Jan 12-Jan 28-Jan 16-Feb 24-Feb 16-Mar 11-Mar 10-Mar 13-Mar 15-Mar 69.5 59.0 41.9 25.6 19.6

1977 22-Dec 27-Dec 06-Jan 15-Jan 17-Jan 31-Mar 30-Mar 26-Mar 31-Mar 03-Apr 101.3 94.9 80.1 76.5 76.6

1978 04-Jan 12-Jan 27-Jan 10-Feb 15-Feb 06-Apr 02-Apr 22-Mar 17-Mar 18-Mar 92.8 80.7 55.0 36.5 32.3

1979 02-Jan 09-Jan 17-Jan 26-Jan 01-Feb 31-Mar 29-Mar 26-Mar 03-Apr 11-Apr 89.6 80.3 69.6 68.4 70.0

1980 19-Jan 29-Jan 08-Feb 08-Feb 15-Feb 24-Mar 22-Mar 18-Mar 16-Mar 10-Mar 64.9 53.3 38.9 36.3 24.1

1981 01-Jan 06-Jan 13-Jan 23-Jan 28-Jan 12-Mar 07-Mar 25-Feb 01-Mar 07-Mar 71.0 61.2 44.1 38.1 38.1

1982 11-Jan 16-Jan 23-Jan 04-Feb 08-Feb 03-Apr 28-Mar 20-Mar 19-Mar 17-Mar 83.5 71.8 57.1 44.0 38.5

1983 18-Jan 20-Jan 21-Jan 29-Jan 31-Jan 02-Mar 23-Feb 10-Feb 16-Feb 24-Feb 43.4 34.9 21.2 18.4 24.8

1984 01-Jan 09-Jan 21-Jan 01-Feb 09-Feb 29-Mar 26-Mar 19-Mar 25-Mar 27-Mar 88.1 77.0 58.9 53.6 46.9

1985 10-Jan 20-Jan 01-Feb 03-Feb 07-Feb 20-Mar 16-Mar 12-Mar 12-Mar 11-Mar 69.8 56.3 40.4 37.9 33.1

1986 29-Dec 07-Jan 28-Jan 04-Feb 13-Feb 26-Mar 23-Mar 17-Mar 19-Mar 20-Mar 88.8 76.1 49.3 43.5 36.6

1987 23-Jan 29-Jan 02-Feb 30-Jan 26-Jan 02-Mar 27-Feb 20-Feb 09-Feb 03-Feb 39.0 30.5 19.8 11.6 9.7

1988 13-Jan 19-Jan 31-Jan 08-Feb 14-Feb 19-Mar 15-Mar 11-Mar 16-Mar 19-Mar 66.2 56.0 40.4 37.4 34.1

1989 09-Jan 26-Jan 07-Feb 14-Feb 19-Feb 04-Apr 31-Mar 03-Apr 07-Apr 11-Apr 85.8 65.0 56.2 53.4 52.4

1990 20-Dec 26-Dec 09-Jan 23-Jan 08-Feb 25-Mar 18-Mar 10-Mar 16-Mar 15-Mar 96.8 84.2 61.2 53.3 35.7

1991 11-Jan 21-Jan 28-Jan 28-Jan 28-Jan 16-Mar 09-Mar 06-Mar 19-Mar 16-Mar 64.9 47.7 38.0 51.1 47.9

1992 13-Jan 24-Jan 09-Feb 23-Feb 02-Mar 30-Mar 22-Mar 22-Mar 25-Mar 24-Mar 76.4 57.3 41.3 31.1 22.8

1993 15-Jan 30-Jan 07-Feb 15-Feb 20-Feb 02-Apr 28-Mar 26-Mar 24-Mar 26-Mar 77.7 58.4 48.0 37.7 34.5

1994 03-Jan 10-Jan 18-Jan 24-Jan 28-Jan 07-Apr 05-Apr 27-Mar 27-Mar 03-Apr 95.3 85.8 69.1 63.5 66.6

1995 23-Jan 05-Feb 16-Feb 25-Feb 26-Feb 20-Mar 17-Mar 12-Mar 10-Mar 13-Mar 57.1 41.3 24.9 14.0 16.1

1996 30-Dec 09-Jan 24-Jan 01-Feb 03-Feb 08-Apr 06-Apr 29-Mar 02-Apr 06-Apr 101.4 88.0 65.0 60.8 62.8

1997 07-Jan 16-Jan 28-Jan 07-Feb 15-Feb 30-Mar 24-Mar 21-Mar 31-Mar 05-Apr 83.2 68.9 53.5 53.1 50.2

1998 10-Jan 18-Jan 26-Jan 23-Jan 14-Jan 04-Mar 01-Mar 19-Feb 05-Feb 28-Jan 53.3 42.4 25.0 13.2 15.2

1999 09-Jan 17-Jan 29-Jan 09-Feb 31-Jan 12-Mar 06-Mar 21-Feb 21-Feb 01-Mar 63.1 49.6 23.4 13.2 30.0

2000 12-Jan 21-Jan 31-Jan 09-Feb 09-Feb 03-Mar 25-Feb 18-Feb 18-Feb 20-Feb 50.6 36.2 19.3 10.1 11.8

2001 30-Dec 07-Jan 30-Jan 21-Feb 28-Feb 24-Mar 19-Mar 08-Mar 21-Mar 27-Mar 86.3 72.1 37.4 28.8 27.9

2002 16-Jan 05-Feb 24-Feb 25-Feb 14-Feb 18-Mar 26-Mar 21-Mar 15-Mar 22-Mar 61.4 49.7 26.0 19.0 37.1

Maximum 23-Jan 05-Feb 24-Feb 25-Feb 02-Mar 08-Apr 06-Apr 03-Apr 07-Apr 11-Apr 101.4 94.9 80.1 76.5 76.6

Minimum 20-Dec 26-Dec 06-Jan 15-Jan 14-Jan 02-Mar 23-Feb 10-Feb 05-Feb 28-Jan 39.0 30.5 19.3 10.1 9.7

Average 08-Jan 17-Jan 28-Jan 05-Feb 09-Feb 22-Mar 18-Mar 12-Mar 14-Mar 16-Mar 74.0 61.0 44.1 37.6 35.7

Median 10-Jan 18-Jan 28-Jan 05-Feb 09-Feb 24-Mar 19-Mar 14-Mar 17-Mar 18-Mar 71.0 57.9 41.6 37.6 34.3

25% of pdf 02-Jan 09-Jan 23-Jan 29-Jan 01-Feb 16-Mar 09-Mar 06-Mar 04-Mar 08-Mar 63.2 49.5 34.5 21.9 23.1

75% of pdf 13-Jan 23-Jan 01-Feb 09-Feb 15-Feb 31-Mar 27-Mar 22-Mar 25-Mar 27-Mar 87.7 75.1 55.9 52.6 46.2

pdf = probability density function of the cumulative frequency distribution.
44 

Table 3.2. Lake Superior statistics for discrete depth ranges for ice cover concentration ≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 25-Dec 02-Jan 12-Jan 02-Feb 13-Feb 22-Mar 16-Mar 11-Mar 06-Mar 02-Mar 88.9 73.9 58.6 32.4 18.7

1974 04-Jan 09-Jan 18-Jan 03-Feb 20-Feb 18-Apr 12-Apr 07-Apr 03-Apr 31-Mar 105.5 93.9 80.1 60.5 39.8

1975 13-Jan 20-Jan 30-Jan 08-Feb 11-Feb 05-Apr 27-Mar 17-Mar 01-Mar 24-Feb 83.0 66.6 47.1 22.0 14.0

1976 04-Jan 13-Jan 27-Jan 16-Feb 28-Feb 01-Apr 22-Mar 18-Mar 16-Mar 17-Mar 88.1 69.0 51.5 29.0 17.9

1977 19-Dec 23-Dec 30-Dec 10-Jan 18-Jan 17-Apr 14-Apr 10-Apr 06-Apr 05-Apr 120.2 113.6 103.5 86.8 78.2

1978 31-Dec 11-Jan 24-Jan 09-Feb 15-Feb 12-Apr 05-Apr 29-Mar 24-Mar 19-Mar 103.3 84.9 65.8 44.4 32.6

1979 30-Dec 05-Jan 10-Jan 21-Jan 31-Jan 01-May 27-Apr 22-Apr 19-Apr 13-Apr 123.6 113.3 103.3 89.2 72.1

1980 12-Jan 21-Jan 29-Jan 04-Feb 17-Feb 04-Apr 29-Mar 24-Mar 18-Mar 11-Mar 83.5 68.4 54.8 42.2 23.3

1981 31-Dec 06-Jan 11-Jan 22-Jan 29-Jan 31-Mar 24-Mar 18-Mar 10-Mar 08-Mar 90.1 78.3 66.8 48.3 38.7

1982 06-Jan 13-Jan 21-Jan 01-Feb 10-Feb 16-Apr 06-Apr 01-Apr 26-Mar 21-Mar 101.5 84.1 71.2 54.2 39.8

1983 08-Jan 17-Jan 21-Jan 28-Jan 31-Jan 19-Mar 04-Mar 18-Feb 18-Feb 23-Feb 71.0 46.3 28.7 21.8 24.4

1984 27-Dec 01-Jan 13-Jan 29-Jan 12-Feb 14-Apr 10-Apr 04-Apr 31-Mar 28-Mar 110.4 100.1 82.7 61.6 45.0

1985 30-Dec 05-Jan 15-Jan 30-Jan 09-Feb 31-Mar 24-Mar 20-Mar 16-Mar 11-Mar 92.0 78.9 65.1 46.1 31.0

1986 26-Dec 03-Jan 15-Jan 30-Jan 13-Feb 03-Apr 29-Mar 27-Mar 24-Mar 22-Mar 99.9 86.2 72.1 54.3 37.9

1987 15-Jan 22-Jan 29-Jan 05-Feb 31-Jan 05-Mar 19-Feb 12-Feb 11-Feb 06-Feb 49.7 29.0 15.6 6.8 7.7

1988 12-Jan 19-Jan 27-Jan 09-Feb 14-Feb 28-Mar 24-Mar 21-Mar 20-Mar 21-Mar 75.9 65.3 54.2 39.8 36.1

1989 28-Dec 05-Jan 15-Jan 05-Feb 20-Feb 23-Apr 19-Apr 17-Apr 13-Apr 12-Apr 117.3 105.2 92.5 68.6 51.5

1990 18-Dec 24-Dec 30-Dec 21-Jan 05-Feb 08-Apr 02-Apr 29-Mar 25-Mar 17-Mar 113.1 101.3 90.6 64.0 41.1

1991 04-Jan 11-Jan 18-Jan 26-Jan 31-Jan 08-Apr 02-Apr 25-Mar 21-Mar 16-Mar 95.0 81.7 67.3 55.4 44.7

1992 23-Dec 07-Jan 29-Jan 22-Feb 04-Mar 14-Apr 05-Apr 01-Apr 28-Mar 24-Mar 113.7 88.9 62.7 35.8 21.0

1993 04-Jan 14-Jan 30-Jan 13-Feb 22-Feb 12-Apr 06-Apr 01-Apr 28-Mar 26-Mar 98.8 82.5 62.6 43.1 33.0

1994 27-Dec 04-Jan 11-Jan 20-Jan 26-Jan 20-Apr 16-Apr 12-Apr 09-Apr 08-Apr 115.7 103.3 92.3 79.6 72.9

1995 13-Jan 31-Jan 15-Feb 26-Feb 27-Feb 04-Apr 25-Mar 17-Mar 11-Mar 14-Mar 81.7 54.3 30.8 13.9 16.4

1996 27-Dec 10-Jan 21-Jan 29-Jan 03-Feb 08-May 01-May 23-Apr 14-Apr 10-Apr 133.7 112.1 92.6 75.9 66.0

1997 30-Dec 12-Jan 23-Jan 05-Feb 17-Feb 22-Apr 16-Apr 13-Apr 08-Apr 06-Apr 114.5 95.4 80.3 62.4 48.3

1998 03-Jan 14-Jan 18-Jan 22-Jan 12-Jan 14-Mar 25-Feb 12-Feb 04-Feb 24-Jan 70.6 42.6 25.7 13.9 12.5

1999 08-Jan 21-Jan 04-Feb 12-Feb 02-Feb 22-Mar 10-Mar 03-Mar 28-Feb 28-Feb 74.6 48.8 27.7 16.5 26.3

2000 05-Jan 18-Jan 30-Jan 11-Feb 06-Feb 11-Mar 01-Mar 24-Feb 20-Feb 20-Feb 65.1 42.4 26.7 9.9 15.1

2001 30-Dec 16-Jan 04-Feb 24-Feb 01-Mar 13-Apr 05-Apr 31-Mar 26-Mar 28-Mar 106.0 80.4 56.5 30.5 28.0

2002 10-Jan 04-Feb 19-Feb 28-Feb 21-Feb 06-Apr 28-Mar 22-Mar 19-Mar 20-Mar 87.5 53.6 32.6 20.0 28.1

Maximum 15-Jan 04-Feb 19-Feb 28-Feb 04-Mar 08-May 01-May 23-Apr 19-Apr 13-Apr 133.7 113.6 103.5 89.2 78.2

Minimum 18-Dec 23-Dec 30-Dec 10-Jan 12-Jan 05-Mar 19-Feb 12-Feb 04-Feb 24-Jan 49.7 29.0 15.6 6.8 7.7

Average 02-Jan 12-Jan 22-Jan 04-Feb 10-Feb 06-Apr 30-Mar 24-Mar 19-Mar 17-Mar 95.8 78.1 62.1 44.3 35.4

Median 02-Jan 11-Jan 21-Jan 04-Feb 11-Feb 07-Apr 31-Mar 26-Mar 23-Mar 19-Mar 96.9 81.1 63.9 43.8 32.8

25% of pdf 27-Dec 05-Jan 15-Jan 28-Jan 01-Feb 31-Mar 24-Mar 17-Mar 11-Mar 08-Mar 83.1 65.6 48.2 23.8 21.6

75% of pdf 07-Jan 18-Jan 29-Jan 11-Feb 19-Feb 16-Apr 09-Apr 04-Apr 30-Mar 28-Mar 112.4 95.0 80.3 61.3 43.8

pdf = probability density function of the cumulative frequency distribution
45

Table 3.3. Lake Michigan statistics for discrete depth ranges for ice cover concentration ≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 02-Jan 08-Jan 19-Jan 28-Jan NA 01-Mar 23-Feb 18-Feb 06-Feb NA 59.5 47.0 30.5 10.4 NA

1974 13-Jan 17-Jan 27-Jan 06-Feb NA 21-Mar 08-Mar 26-Feb 27-Feb NA 68.3 51.2 30.7 21.2 NA

1975 14-Jan 20-Jan 27-Jan 02-Feb 22-Jan 23-Mar 12-Mar 21-Feb 14-Feb 22-Jan 68.6 51.8 25.6 12.8 1.0

1976 03-Jan 12-Jan 31-Jan 16-Feb 29-Jan 12-Mar 06-Mar 22-Feb 22-Feb 07-Feb 68.6 54.1 22.7 7.3 10.0

1977 21-Dec 26-Dec 12-Jan 20-Jan 25-Jan 30-Mar 26-Mar 18-Mar 23-Mar 30-Mar 101.0 91.6 66.3 62.6 65.2

1978 06-Jan 16-Jan 02-Feb 16-Feb 25-Feb 30-Mar 25-Mar 13-Mar 09-Mar 11-Mar 84.1 69.5 39.9 21.3 14.9

1979 31-Dec 06-Jan 16-Jan 28-Jan 14-Feb 30-Mar 25-Mar 14-Mar 15-Mar 24-Mar 89.8 79.3 58.0 46.9 39.2

1980 19-Jan 29-Jan 12-Feb 11-Feb 19-Feb 18-Mar 12-Mar 05-Mar 05-Mar 19-Feb 59.1 43.0 22.1 22.7 1.0

1981 31-Dec 04-Jan 13-Jan 19-Jan 27-Jan 07-Mar 26-Feb 09-Feb 31-Jan 28-Jan 67.6 54.0 28.1 13.1 1.6

1982 11-Jan 15-Jan 25-Jan 07-Feb 10-Feb 21-Mar 15-Mar 04-Mar 04-Mar 17-Feb 69.9 59.2 39.7 26.6 7.9

1983 18-Jan 22-Jan 28-Jan 02-Feb NA 06-Mar 26-Feb 19-Feb 13-Feb NA 47.3 35.8 23.6 11.6 NA

1984 09-Jan 16-Jan 27-Jan 18-Jan 02-Jan 13-Mar 07-Mar 24-Feb 21-Feb 02-Jan 64.5 50.9 28.4 34.4 1.0

1985 12-Jan 24-Jan 11-Feb 24-Feb NA 19-Mar 13-Mar 04-Mar 04-Mar NA 67.0 49.6 21.4 9.1 NA

1986 30-Dec 14-Jan 02-Feb 08-Feb 24-Feb 22-Mar 17-Mar 06-Mar 06-Mar 01-Mar 82.8 62.9 33.4 26.8 6.7

1987 18-Jan 24-Jan 29-Jan 29-Jan NA 23-Feb 28-Feb 19-Feb 19-Feb NA 36.3 35.5 21.7 22.0 NA

1988 14-Jan 20-Jan 22-Jan 26-Jan NA 11-Mar 02-Mar 16-Feb 11-Feb NA 57.8 42.5 26.4 17.9 NA

1989 12-Jan 27-Jan 16-Feb 26-Feb 06-Mar 01-Apr 26-Mar 23-Mar 23-Mar 13-Mar 80.6 59.7 36.0 26.3 7.2

1990 18-Dec 24-Dec 12-Jan 25-Jan 03-Mar 21-Mar 10-Mar 19-Feb 02-Mar 03-Mar 95.9 78.4 39.3 37.1 1.0

1991 05-Jan 17-Jan 31-Jan 17-Feb NA 11-Mar 04-Mar 28-Feb 13-Mar NA 65.4 46.8 28.9 24.1 NA

1992 08-Jan 18-Jan 29-Jan 02-Feb 02-Feb 11-Mar 01-Mar 15-Feb 10-Feb 02-Feb 62.6 43.2 18.3 8.5 1.0

1993 16-Jan 29-Jan 12-Feb 22-Feb 28-Feb 20-Mar 14-Mar 13-Mar 06-Mar 28-Feb 64.3 45.0 29.8 13.3 1.0

1994 04-Jan 13-Jan 26-Jan 30-Jan 06-Feb 30-Mar 25-Mar 13-Mar 10-Mar 10-Mar 86.1 71.6 46.8 39.9 33.2

1995 28-Jan 10-Feb 23-Feb 01-Mar NA 14-Mar 09-Mar 02-Mar 02-Mar NA 45.8 28.4 7.9 1.9 NA

1996 01-Jan 13-Jan 31-Jan 04-Feb 05-Feb 06-Apr 02-Apr 13-Mar 11-Mar 15-Mar 96.7 80.6 41.5 35.7 38.8

1997 01-Jan 11-Jan 24-Jan 10-Feb 17-Feb 24-Mar 15-Mar 24-Feb 01-Mar 17-Feb 83.0 63.2 31.9 19.3 1.0

1998 13-Jan 18-Jan 28-Jan 26-Jan NA 04-Mar 27-Feb 01-Feb 26-Jan NA 51.1 40.9 5.1 1.0 NA

1999 07-Jan 12-Jan 23-Jan 04-Feb NA 28-Feb 24-Feb 11-Feb 19-Feb NA 53.6 44.5 19.9 15.5 NA

2000 11-Jan 20-Jan 27-Jan 29-Jan NA 28-Feb 20-Feb 08-Feb 01-Feb NA 49.3 31.6 12.7 4.1 NA

2001 24-Dec 05-Jan 18-Jan 05-Feb NA 19-Mar 09-Mar 08-Feb 08-Feb NA 87.0 64.0 21.3 4.2 NA

2002 17-Jan 08-Feb 08-Mar 12-Mar NA 19-Mar 25-Mar 20-Mar 12-Mar NA 61.7 46.3 13.4 1.0 NA

Maximum 28-Jan 10-Feb 08-Mar 12-Mar 06-Feb 06-Apr 02-Apr 23-Mar 23-Mar 30-Mar 101.0 91.6 66.3 62.6 65.2

Minimum 18-Dec 24-Dec 12-Jan 18-Jan 06-Mar 23-Feb 20-Feb 01-Feb 26-Jan 02-Jan 36.3 28.4 5.1 1.0 1.0

Average 07-Jan 16-Jan 30-Jan 06-Feb 02-Jan 17-Mar 11-Mar 27-Feb 25-Feb 22-Feb 69.2 54.1 29.0 20.0 13.6

Median 08-Jan 17-Jan 28-Jan 04-Feb 09-Feb 19-Mar 10-Mar 25-Feb 01-Mar 28-Feb 67.3 51.1 28.3 18.6 6.7

25% of pdf 01-Jan 12-Jan 24-Jan 28-Jan 08-Feb 11-Mar 01-Mar 18-Feb 13-Feb 07-Feb 59.2 43.5 21.5 9.4 1.0

75% of pdf 13-Jan 21-Jan 01-Feb 14-Feb 30-Jan 23-Mar 16-Mar 11-Mar 08-Mar 11-Mar 83.0 63.1 35.4 26.5 14.9

pdf = probability density function of the cumulative frequency distribution

NA = no data meeting threshold ice concentration
46 

Table 3.4. Lake Huron statistics for discrete depth ranges for ice cover concentration ≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 30-Dec 13-Jan 06-Feb 13-Feb 19-Feb 14-Mar 12-Mar 07-Mar 02-Mar 26-Feb 76.1 58.8 30.4 18.8 8.0

1974 09-Jan 20-Jan 06-Feb 21-Feb 27-Feb 01-Apr 23-Mar 16-Mar 12-Mar 27-Mar 83.2 63.1 38.6 20.1 29.0

1975 19-Jan 29-Jan 11-Feb 04-Feb 05-Feb 05-Apr 23-Mar 08-Mar 18-Feb 05-Feb 77.3 54.5 26.7 14.6 1.0

1976 30-Dec 05-Jan 26-Jan 20-Feb 02-Mar 27-Mar 21-Mar 15-Mar 07-Mar 02-Mar 87.5 76.2 49.1 15.8 1.0

1977 18-Dec 25-Dec 05-Jan 16-Jan 24-Jan 05-Apr 02-Apr 28-Mar 31-Mar 06-Apr 109.8 99.3 83.6 74.4 72.9

1978 30-Dec 10-Jan 23-Jan 04-Feb 08-Feb 09-Apr 04-Apr 28-Mar 22-Mar 16-Mar 101.4 84.4 64.9 47.8 37.3

1979 30-Dec 06-Jan 17-Jan 31-Jan 06-Feb 04-Apr 28-Mar 27-Mar 26-Mar 25-Mar 96.9 81.9 70.6 55.2 47.5

1980 15-Jan 28-Jan 12-Feb 25-Feb 05-Feb 30-Mar 28-Mar 23-Mar 16-Mar 05-Feb 75.6 60.2 40.1 19.6 1.0

1981 31-Dec 06-Jan 15-Jan 28-Jan 03-Feb 19-Mar 10-Mar 03-Mar 27-Feb 28-Feb 79.5 64.3 47.8 30.8 26.5

1982 09-Jan 16-Jan 23-Jan 07-Feb 18-Feb 12-Apr 03-Apr 27-Mar 18-Mar 17-Mar 93.6 77.7 63.7 39.9 28.1

1983 17-Jan 19-Jan 18-Jan 17-Jan NA 04-Mar 25-Feb 02-Feb 25-Jan NA 47.2 38.0 16.0 9.0 NA

1984 30-Dec 08-Jan 21-Jan 10-Feb 11-Feb 04-Apr 29-Mar 24-Mar 16-Mar 11-Mar 96.7 81.2 63.7 35.4 29.6

1985 07-Jan 19-Jan 04-Feb 14-Feb 13-Feb 27-Mar 20-Mar 13-Mar 28-Feb 22-Feb 80.3 61.3 37.8 15.7 9.3

1986 24-Dec 08-Jan 29-Jan 12-Feb 01-Mar 29-Mar 27-Mar 22-Mar 20-Mar 14-Mar 97.4 79.2 53.6 36.3 13.7

1987 20-Jan 28-Jan 06-Feb 31-Jan NA 09-Mar 04-Mar 26-Feb 21-Feb NA 49.0 36.1 20.8 22.1 NA

1988 10-Jan 21-Jan 07-Feb 16-Feb 06-Feb 27-Mar 24-Mar 19-Mar 10-Mar 06-Mar 76.7 62.9 41.0 23.7 29.0

1989 02-Jan 20-Jan 13-Feb 08-Mar 13-Mar 11-Apr 08-Apr 02-Apr 24-Mar 20-Mar 100.1 78.3 48.8 16.8 8.5

1990 17-Dec 26-Dec 10-Jan 01-Feb 10-Feb 30-Mar 23-Mar 16-Mar 04-Mar 08-Mar 104.6 88.3 65.7 31.7 27.3

1991 08-Jan 17-Jan 31-Jan 07-Feb NA 22-Mar 09-Mar 26-Feb 21-Feb NA 73.8 52.4 26.9 15.4 NA

1992 07-Jan 26-Jan 20-Feb 04-Mar 15-Mar 13-Apr 04-Apr 28-Mar 25-Mar 23-Mar 96.6 68.4 37.4 22.0 9.7

1993 06-Jan 22-Jan 06-Feb 22-Feb 04-Mar 10-Apr 02-Apr 27-Mar 16-Mar 06-Mar 95.2 71.8 49.2 23.2 3.6

1994 01-Jan 07-Jan 14-Jan 24-Jan 26-Jan 15-Apr 12-Apr 06-Apr 01-Apr 27-Mar 104.8 96.4 82.8 67.5 60.7

1995 17-Jan 04-Feb 16-Feb 22-Feb NA 26-Mar 20-Mar 13-Mar 08-Mar NA 69.4 44.9 26.4 14.9 NA

1996 22-Dec 05-Jan 21-Jan 02-Feb 11-Feb 16-Apr 10-Apr 05-Apr 26-Mar 19-Mar 116.3 96.3 75.1 53.2 36.5

1997 04-Jan 17-Jan 30-Jan 11-Feb 19-Feb 11-Apr 01-Apr 26-Mar 17-Mar 26-Feb 97.6 75.3 56.1 34.1 7.3

1998 10-Jan 20-Jan 06-Feb 13-Feb NA 13-Mar 06-Mar 28-Feb 23-Feb NA 63.1 46.3 23.6 11.5 NA

1999 05-Jan 18-Jan 27-Jan 22-Jan NA 16-Mar 08-Mar 15-Feb 27-Jan NA 70.2 49.3 20.1 5.6 NA

2000 07-Jan 21-Jan 03-Feb 25-Jan NA 08-Mar 01-Mar 19-Feb 28-Jan NA 61.2 40.1 16.9 3.5 NA

2001 22-Dec 07-Jan 05-Feb 16-Feb NA 03-Apr 24-Mar 11-Mar 06-Mar NA 103.7 77.5 35.2 19.0 NA

2002 16-Jan 08-Feb 05-Mar 14-Mar NA 31-Mar 26-Mar 21-Mar 14-Mar NA 74.4 47.0 16.3 1.0 NA

Maximum 20-Jan 08-Feb 05-Mar 14-Mar 15-Mar 16-Apr 12-Apr 06-Apr 01-Apr 06-Apr 116.3 99.3 83.6 74.4 72.9

Minimum 17-Dec 25-Dec 05-Jan 16-Jan 24-Jan 04-Mar 25-Feb 02-Feb 25-Jan 05-Feb 47.2 36.1 16.0 1.0 0.0

Average 04-Jan 16-Jan 31-Jan 10-Feb 15-Feb 29-Mar 23-Mar 15-Mar 07-Mar 12-Mar 85.3 67.0 44.3 26.6 22.2

Median 06-Jan 18-Jan 01-Feb 11-Feb 12-Feb 30-Mar 24-Mar 17-Mar 11-Mar 11-Mar 85.4 66.4 40.6 21.1 26.5

25% of pdf 30-Dec 07-Jan 21-Jan 31-Jan 06-Feb 23-Mar 14-Mar 08-Mar 27-Feb 28-Feb 74.7 52.9 26.8 15.5 7.5

75% of pdf 10-Jan 21-Jan 06-Feb 19-Feb 25-Feb 08-Apr 01-Apr 27-Mar 19-Mar 20-Mar 97.6 79.0 61.8 35.1 29.5

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
47

Table 3.5. Lake Erie statistics for discrete depth ranges for ice cover concentration ≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 16-Jan 07-Feb 19-Feb NA NA 02-Mar 04-Mar 05-Mar NA NA 45.6 26.5 15.1 NA NA

1974 13-Jan 31-Jan 22-Jan NA NA 28-Feb 06-Mar 12-Mar NA NA 46.5 35.4 50.3 NA NA

1975 26-Jan 12-Feb 25-Feb NA NA 08-Mar 05-Mar 04-Mar NA NA 41.1 21.8 8.8 NA NA

1976 07-Jan 17-Jan 25-Jan NA NA 23-Feb 26-Feb 08-Mar NA NA 47.8 41.3 43.0 NA NA

1977 21-Dec 28-Dec 29-Dec NA NA 18-Mar 27-Mar 29-Mar NA NA 89.2 91.7 91.0 NA NA

1978 30-Dec 07-Jan 14-Jan NA NA 05-Apr 11-Apr 11-Apr NA NA 96.9 95.2 87.9 NA NA

1979 02-Jan 11-Jan 13-Jan NA NA 19-Mar 26-Mar 30-Mar NA NA 76.6 75.6 77.0 NA NA

1980 23-Jan 03-Feb 03-Feb NA NA 20-Mar 24-Mar 04-Apr NA NA 56.7 50.5 60.8 NA NA

1981 02-Jan 06-Jan 06-Jan NA NA 03-Mar 09-Mar 29-Mar NA NA 61.2 63.2 83.0 NA NA

1982 13-Jan 17-Jan 17-Jan NA NA 28-Mar 02-Apr 11-Apr NA NA 74.7 76.2 85.8 NA NA

1983 27-Jan 23-Jan 17-Jan NA NA 16-Feb 25-Jan 17-Jan NA NA 21.4 3.0 1.0 NA NA

1984 30-Dec 01-Jan 02-Jan NA NA 01-Apr 04-Apr 10-Apr NA NA 94.1 93.9 99.1 NA NA

1985 15-Jan 25-Jan 30-Jan NA NA 10-Mar 15-Mar 28-Mar NA NA 55.1 50.0 58.1 NA NA

1986 25-Dec 27-Dec 27-Dec NA NA 21-Mar 24-Mar 01-Apr NA NA 88.0 88.6 96.3 NA NA

1987 27-Jan 05-Feb 16-Feb NA NA 27-Feb 26-Feb 27-Feb NA NA 31.5 22.0 11.4 NA NA

1988 08-Jan 15-Jan 09-Jan NA NA 14-Mar 18-Mar 03-Apr NA NA 65.9 62.6 85.6 NA NA

1989 17-Jan 06-Feb 03-Feb NA NA 18-Mar 17-Mar 17-Mar NA NA 60.3 39.8 43.2 NA NA

1990 18-Dec 24-Dec 24-Dec NA NA 13-Mar 14-Mar 17-Mar NA NA 86.6 81.6 84.9 NA NA

1991 19-Jan 06-Feb 08-Feb NA NA 02-Mar 01-Mar 04-Mar NA NA 43.1 24.3 24.4 NA NA

1992 23-Jan 03-Feb 07-Feb NA NA 19-Mar 15-Mar 17-Mar NA NA 56.0 41.4 38.9 NA NA

1993 25-Jan 15-Feb 16-Feb NA NA 30-Mar 30-Mar 01-Apr NA NA 64.4 43.4 44.4 NA NA

1994 05-Jan 13-Jan 15-Jan NA NA 28-Mar 04-Apr 17-Apr NA NA 83.5 82.9 92.6 NA NA

1995 21-Jan 07-Feb 11-Feb NA NA 15-Mar 20-Mar 21-Mar NA NA 54.0 41.7 39.4 NA NA

1996 26-Dec 08-Jan 13-Jan NA NA 25-Mar 30-Mar 02-Apr NA NA 91.1 82.0 79.9 NA NA

1997 09-Jan 17-Jan 23-Jan NA NA 06-Mar 12-Mar 23-Mar NA NA 57.0 54.7 59.2 NA NA

1998 13-Jan 28-Jan NA NA NA 28-Jan 28-Jan NA NA NA 16.2 1.0 NA NA NA

1999 07-Jan 15-Jan 24-Jan NA NA 13-Mar 10-Mar 07-Mar NA NA 66.1 55.5 42.8 NA NA

2000 17-Jan 26-Jan 25-Jan NA NA 27-Feb 27-Feb 01-Mar NA NA 42.7 33.5 36.2 NA NA

2001 23-Dec 01-Jan 10-Jan NA NA 08-Mar 17-Mar 09-Apr NA NA 76.3 76.3 90.1 NA NA

2002 10-Jan 12-Feb NA NA NA 02-Feb 12-Feb NA NA NA 24.1 1.0 NA NA NA

Maximum 27-Jan 15-Feb 25-Feb NA NA 05-Apr 11-Apr 17-Apr NA NA 96.9 95.2 99.1 NA NA

Minimum 18-Dec 24-Dec 24-Dec NA NA 28-Jan 25-Jan 17-Jan NA NA 16.2 1.0 1.0 NA NA

Average 10-Jan 21-Jan 23-Jan NA NA 10-Mar 13-Mar 21-Mar NA NA 60.5 51.9 58.2 NA NA

Median 11-Jan 20-Jan 23-Jan NA NA 13-Mar 15-Mar 25-Mar NA NA 58.7 50.3 58.7 NA NA

25% of pdf 02-Jan 09-Jan 12-Jan NA NA 02-Mar 05-Mar 08-Mar NA NA 45.8 34.0 39.3 NA NA

75% of pdf 18-Jan 05-Feb 04-Feb NA NA 19-Mar 26-Mar 03-Apr NA NA 76.5 76.3 85.7 NA NA

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
48 

Table 3.6. Lake Ontario statistics for discrete depth ranges for ice cover concentration ≥ 10%.

Winter

Season

a) Average date of First Ice b) Average date of Last Ice c) Average Duration (days) 

Depth Range (m) Depth Range (m) Depth Range (m)

0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200 0-20 21-50 51-100 101-200 >200

1973 13-Jan 19-Jan 02-Feb 08-Feb NA 28-Feb 26-Feb 21-Feb 18-Feb NA 47.2 38.2 20.1 11.1 NA

1974 13-Jan 19-Jan 22-Jan 27-Jan 20-Feb 24-Feb 18-Feb 02-Feb 04-Feb 20-Feb 42.9 31.4 12.7 8.7 1.0

1975 27-Jan 05-Feb 12-Feb NA NA 05-Mar 18-Feb 12-Feb NA NA 38.0 14.0 1.0 NA NA

1976 09-Jan 27-Jan 25-Jan 31-Jan NA 05-Mar 16-Feb 29-Jan 01-Feb NA 56.0 21.0 4.3 1.6 NA

1977 01-Jan 07-Jan 12-Jan 28-Jan 04-Feb 19-Mar 13-Mar 28-Feb 05-Mar 11-Mar 77.5 66.7 48.4 36.5 35.8

1978 12-Jan 23-Jan 06-Feb 14-Feb 14-Feb 21-Mar 15-Mar 05-Mar 26-Feb 03-Mar 68.6 51.3 28.3 12.9 18.2

1979 17-Jan 24-Jan 01-Feb 10-Feb 02-Feb 08-Mar 01-Mar 26-Feb 22-Feb 20-Feb 50.9 36.5 25.8 12.7 19.3

1980 30-Jan 05-Feb 13-Feb 16-Feb 10-Feb 10-Mar 07-Mar 05-Mar 27-Feb 12-Feb 39.7 31.5 21.4 11.5 2.2

1981 06-Jan 07-Jan 10-Jan 17-Jan 12-Jan 16-Feb 10-Feb 23-Jan 21-Jan 14-Jan 42.3 35.6 14.0 5.5 3.3

1982 16-Jan 17-Jan 20-Jan 04-Feb 04-Mar 19-Mar 14-Mar 02-Mar 26-Feb 08-Mar 62.4 57.0 41.7 22.7 4.6

1983 27-Jan 30-Jan 31-Jan NA NA 15-Feb 09-Feb 01-Feb NA NA 19.4 10.7 2.3 NA NA

1984 10-Jan 15-Jan 24-Jan 04-Feb 07-Feb 09-Mar 12-Mar 21-Feb 11-Feb 07-Feb 58.9 57.5 29.1 8.1 1.0

1985 17-Jan 24-Jan 02-Feb 08-Feb 08-Feb 08-Mar 03-Mar 21-Feb 21-Feb 22-Feb 51.0 38.9 20.3 14.0 15.0

1986 11-Jan 18-Jan 06-Feb 15-Feb 01-Mar 15-Mar 14-Mar 07-Mar 06-Mar 07-Mar 64.1 56.2 30.2 19.8 6.1

1987 05-Feb 12-Feb NA NA NA 07-Mar 23-Feb NA NA NA 30.9 12.4 NA NA NA

1988 12-Jan 18-Jan 27-Jan 18-Feb NA 26-Feb 20-Feb 03-Feb 26-Feb NA 45.7 34.8 7.6 8.8 NA

1989 11-Feb 24-Feb 05-Mar 12-Mar NA 20-Mar 14-Mar 09-Mar 14-Mar NA 38.3 18.8 4.7 3.5 NA

1990 31-Dec 07-Jan 27-Jan 13-Jan 23-Dec 16-Mar 10-Mar 27-Feb 02-Feb 23-Dec 76.9 62.9 32.8 21.6 1.0

1991 15-Jan 23-Jan 28-Jan 26-Jan NA 27-Feb 19-Feb 29-Jan 26-Jan NA 43.9 28.8 1.3 1.0 NA

1992 24-Jan 31-Jan 04-Feb 12-Feb 15-Feb 11-Mar 05-Mar 18-Feb 21-Feb 15-Feb 47.0 34.7 14.8 9.7 1.0

1993 24-Jan 09-Feb 21-Feb 01-Mar 04-Mar 26-Mar 20-Mar 08-Mar 14-Mar 16-Mar 62.1 40.5 16.0 14.1 13.4

1994 06-Jan 11-Jan 21-Jan 01-Feb 05-Feb 21-Mar 16-Mar 27-Feb 24-Feb 06-Mar 74.6 64.6 37.8 23.8 29.9

1995 02-Feb 07-Feb 14-Feb 18-Feb 19-Feb 07-Mar 27-Feb 19-Feb 18-Feb 19-Feb 33.7 20.4 6.4 1.0 1.0

1996 12-Jan 14-Jan 20-Jan 11-Feb 14-Feb 08-Mar 03-Mar 15-Feb 23-Feb 19-Feb 56.0 49.5 27.0 13.5 5.8

1997 18-Jan 24-Jan 11-Feb 18-Feb NA 17-Mar 10-Mar 17-Feb 18-Feb NA 59.2 46.0 7.2 1.0 NA

1998 19-Jan 27-Jan 29-Jan 29-Jan NA 19-Feb 04-Feb 29-Jan 29-Jan NA 31.9 9.7 1.0 1.0 NA

1999 08-Jan 24-Jan 15-Feb 20-Feb NA 03-Mar 03-Mar 28-Feb 02-Mar NA 55.4 39.4 14.1 11.4 NA

2000 16-Jan 23-Jan 30-Jan 07-Feb NA 19-Feb 14-Feb 06-Feb 07-Feb NA 34.9 22.6 7.1 1.0 NA

2001 31-Dec 11-Jan 10-Feb 17-Feb NA 02-Mar 23-Feb 18-Feb 17-Feb NA 62.1 44.1 9.2 1.0 NA

2002 14-Jan 13-Jan NA NA NA 19-Feb 25-Jan NA NA NA 37.6 12.6 0.0 0.0 NA

Maximum 11-Feb 24-Feb 05-Mar 12-Mar 04-Mar 26-Mar 20-Mar 09-Mar 14-Mar 16-Mar 77.5 66.7 48.4 36.5 35.8

Minimum 31-Dec 07-Jan 10-Jan 13-Jan 23-Dec 15-Feb 25-Jan 23-Jan 21-Jan 23-Dec 19.4 9.7 1.0 1.0 1.0

Average 16-Jan 23-Jan 01-Feb 09-Feb 09-Feb 06-Mar 28-Feb 18-Feb 18-Feb 18-Feb 50.3 36.3 17.4 10.7 9.9

Median 14-Jan 23-Jan 31-Jan 09-Feb 12-Feb 07-Mar 02-Mar 20-Feb 21-Feb 20-Feb 49.1 36.1 14.5 10.4 5.2

25% of pdf 10-Jan 15-Jan 25-Jan 31-Jan 05-Feb 27-Feb 18-Feb 05-Feb 08-Feb 14-Feb 38.7 21.4 6.9 2.1 1.0

75% of pdf 22-Jan 29-Jan 10-Feb 16-Feb 19-Feb 16-Mar 12-Mar 28-Feb 26-Feb 06-Mar 61.4 48.6 27.3 13.9 15.8

pdf = probability density function of the cumulative frequency distribution.

NA = no data meeting threshold ice concentration.
49

Table 4. Frequency of Winters Without Freeze-up 

at the west arm of Grand Traverse Bay**.

Grand Traverse Bay, Lake Michigan

Five 30-year periods

Start End Frequency*

1853 1882 5

1883 1912 2

1913 1942 5

1943 1972 5

1973 2002 16

*Number of winters during the 30-winter period that the 

 bay did not freeze-up

** Date updated from Assel 2001