1

NOAA Technical Memorandum GLERL-134 

________________________________________________________________________ 

Conditional Probability of 

December and January Ice Cover 

at Selected Great Lakes Shore Sites 

Raymond A. Assel 

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

Great Lakes Environmental Research Laboratory 

Ann Arbor, Michigan 

June 2005 

________________________________________________________________________ 

UNITED STATES NATIONAL OCEANIC AND 

DEPARTMENT OF COMMERCE ATMOSPHERIC 

 ADMINISTRATION

Carlos M. Gutierrez Conrad C. Lautenbacher, Jr. 

Secretary Administrator 
2

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. 1360. 

This publication is available as a PDF 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. 
3

TABLE OF CONTENTS 

INTRODUCTION-----------------------------------------------------------------------------------6

METHODS-------------------------------------------------------------------------------------------7

RESULTS --------------------------------------------------------------------------------------------8

DISCUSSION----------------------------------------------------------------------------------------9

Site 1, West Tip of Lake Superior-----------------------------------------------------------------9

Site 2, North St. Marys River -------------------------------------------------------------------- 10

Site 3, Straits of Mackinac ----------------------------------------------------------------------- 10

Site 4, Big Bay De Noc --------------------------------------------------------------------------- 10

Site 5, Little Bay De Noc------------------------------------------------------------------------- 10

Site 6, Southern Green Bay ---------------------------------------------------------------------- 10

Site 7, Saginaw Bay ------------------------------------------------------------------------------- 11

Site 8, West Lake Erie ---------------------------------------------------------------------------- 11

CONCLUDING REMARKS -------------------------------------------------------------------- 11 

REFERENCES ------------------------------------------------------------------------------------ 28 

APPENDIX SUMMARY OF REGRESSION ANALYSIS --------------------------------- 29 

LIST OF FIGURES 

 1. Location of Ice Cover Sites------------------------------------------------------------------- 6 

 2. Site 1, West Tip of Lake Superior, December FDDs at Duluth, MN -------------------12 

 3. Site 1, West Tip of Lake Superior, January FDDs at Duluth, MN ----------------------13 

 4. Site 2, North St. Marys River, December FDDs at Sault Ste. Marie, MI --------------14 

 5. Site 2, North St. Marys River, January FDDs at Sault Ste. Marie, MI -----------------15 
4

 6. Site 3, Straits of Mackinac, December FDDs at Alpena, MI ----------------------------16 

 7. Site 3, Straits of Mackinac, January FDDs at Alpena, MI -------------------------------17 

 8. Site 4, Big Bay De Noc, December FDDs at Green Bay, WI ---------------------------18 

 9. Site 4, Big Bay De Noc, January FDDs at Green Bay, WI ------------------------------19 

10. Site 5, Little Bay De Noc, December FDDs at Green Bay, WI -------------------------20 

11. Site 5, Little Bay De Noc, January FDDs at Green Bay, WI ----------------------------21 

12. Site 6, South Green Bay, December FDDs at Green Bay, WI --------------------------22 

13. Site 6, South Green Bay, January FDDs at Green Bay, WI -----------------------------23 

14. Site 7, Saginaw Bay, December FDDs at Alpena, MI -----------------------------------24 

15. Site 7, Saginaw Bay, January FDDs at Alpena, MI --------------------------------------25 

16. Site 8, West Lake Erie, December FDDs at Toledo, OH --------------------------------26 

17. Site 8, West Lake Erie, January FDDs at Toledo, OH -----------------------------------27 

LIST OF TABLES 

 1. Ice Sites, FDD Stations, and Median Water Depth--------------------------------------- 8 

 2. Site 1, West Tip of Lake Superior, December FDDs at Duluth, MN -------------------12 

 3. Site 1, West Tip of Lake Superior, January FDDs at Duluth, MN ----------------------13 

 4. Site 2, North St. Marys River, December FDDs at Sault Ste. Marie, MI --------------14 

 5. Site 2, North St. Marys River, January FDDs at Sault Ste. Marie, MI -----------------15 

 6. Site 3, Straits of Mackinac, December FDDs at Alpena, MI ----------------------------16 

 7. Site 3, Straits of Mackinac, January FDDs at Alpena, MI -------------------------------17 

 8. Site 4, Big Bay De Noc, December FDDs at Green Bay, WI ---------------------------18 

 9. Site 4, Big Bay De Noc, January FDDs at Green Bay, WI ------------------------------19 
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10. Site 5, Little Bay De Noc, December FDDs at Green Bay, WI -------------------------20 

11. Site 5, Little Bay De Noc, January FDDs at Green Bay, WI ----------------------------21 

12. Site 6, South Green Bay, December FDDs at Green Bay, WI --------------------------22 

13. Site 6, South Green Bay, January FDDs at Green Bay, WI -----------------------------23 

14. Site 7, Saginaw Bay, December FDDs at Alpena, MI -----------------------------------24 

15. Site 7, Saginaw Bay, January FDDs at Alpena, MI --------------------------------------25 

16. Site 8, West Lake Erie, December FDDs at Toledo, OH --------------------------------26 

17. Site 8, West Lake Erie, January FDDs at Toledo, OH -----------------------------------27 
6

CONDITIONAL PROBABILITY OF DECEMBER 

AND JANUARY ICE COVER AT SELECTED 

GREAT LAKES SHORE SITES

Raymond A. Assel 

INTRODUCTION 

The National Weather Service (NWS) in Cleveland, Ohio requested improved 

information on ice cover for use in making outlooks of early winter ice cover at eight 

locations in the shore region of the Great Lakes (Fig. 1) (personal communication, Will 

Kubina). Bilello (1964) developed an empirical water temperature decline model to 

simulate the date of initial ice formation on bays and harbors. Greene (1983) applied the 

Billelo model to several sites along the St. Marys River. Assel and Norton (unpublished) 

applied the model to several additional Great Lakes shore sites, modified it for 

operational use, and provided it to the NWS in the mid-to-late 1980s. In this paper, 

empirical freezing degree-day (FDD) conditional probability and linear regression 

models of spatial average ice cover are described and discussed. These models are 

applied to the eight sites of interest to the NWS to estimate early winter (December and 

January) spatial average ice cover. 

Figure 1. Location of ice cover sites. 
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METHODS 

Accumulated freezing degree-days were related to spatial average ice cover. The FDDs 

were calculated at stations that the NWS currently maintains for operational applications 

each winter. FDDs are calculated as the difference between the mean daily air 

temperature and the freezing point of fresh water. Positive (negative) FDDs accumulate 

for a given day when the mean daily air temperature is below (above) 320

F. The daily 

FDD values are summed to keep a cumulative value through each day from October 1 to 

May 31. If the cumulative value becomes negative on a given date, a new value is started 

the next day. FDDs have been found to correlate with spatial average ice cover (Assel 

1991). 

In this study the spatial averaged ice cover was calculated at the eight sites of interest to 

the NWS (Table 1). Spatial variations of ice cover on a given date in some of the sites 

can vary from open water to 100%, because winds can compact the ice cover or move it 

out of an area. Also some of these areas have sufficient variations in water depths so the 

shallower areas form ice earlier. For these reasons the spatial average ice cover is most 

likely to be representative of the entire area of a given site only if it is less than 25% (i.e., 

the site is mostly open water) or it is over 76% (i.e., the site is mostly ice covered). 

Spatial averaged ice cover was calculated using original ice cover data, which is on a 5 x 

5 km grid cell spatial resolution, and was obtained from digitized ice chart observations 

given in Assel (2003) over 30 winters:1973-2002. Accumulations of FDDs at selected 

stations (Table 1) were calculated from October 1 to the date of the observed ice cover at 

each site for each of the 30-winter seasons. The FDD stations were chosen based on 

continuity of data record for the 30-winter period of the study and were also based on a 

statistical correlation analysis between FDD and ice cover. 

These data were partitioned into months for further analysis. The empirical conditional 

probability of 4 ranges of spatial averaged ice cover (≤ 25%, 26-50%, 51-75%, and ≥

76%) was calculated for 10 discrete FDD accumulation ranges (< 200, 200-399, 400-599, 

600-799, 800-999, 1000-1199, 1200-1399, 1400-1599, 1600-1799, and1800-1999) for the 

months of December and January for each of the 8 sites. 

These data are presented as ranges of FDD and ranges of spatial averaged ice cover. The 

FDD on a given date in December or January is used to calculate the conditional 

probability (see Chapter 3 of Meyer 1966) of a spatial average ice cover being in one of 

the four ranges: 0-25%, 26-50%, 51-75%, 76-100% given a range of FDD values, e.g. 

200 - 399 FDD. As an example (from Table 2), the total number of observations for 

December (at Duluth, Minnesota) for FDD between 200 and 399 is 45. Of this number, 0 

occurred for ice cover between 76%-100%, 4 occurred for ice cover between 51%-75%, 

9 occurred for ice cover between 26%-50%, and 32 occurred for ice cover between 0%-

25%. Therefore the conditional probability of ice cover between 76%-100% for FDD 
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between 200 and 399 at Duluth in December is 0% [(0/45) x 100), the conditional 

probability of ice cover between 51%-75% for FDD between 200 and 399 at Duluth in 

December is 8.9% [ (4/45) x 100], the conditional probability of ice cover between 26%-

50% for FDD between 200 and 399 at Duluth in December is 20% [(9/45) x 100], and 

the conditional probability of ice cover between 0%-25% for FDD between 200 and 399 

at Duluth in December is 71.1% [(32/45) x 100]. If you add all of the partial conditional 

probabilities for FDD between 200 and 399 at Duluth for December you get 100% (0% + 

8.9% + 20% + 71.1%). In the table 0% conditional probability is replaced by “*” to 

simplify readability. 

Simple linear regression models of FDD vs. ice cover were also developed for each site 

for December and January. The FDD regression provides an alternative method for 

estimating spatial average ice cover. Regression equations were calculated using Quattro 

Pro. Operational application of regression equations are constrained to operate in the 

range of FDD values for which they will not produce negative ice cover or ice cover 

greater than 100%. For FDD at the lower limit, the regression output’s 0% ice cover and 

for the upper limit of FDD, the regression output’s 100% ice cover. Results are 

summarized in an Appendix. 

Table 1 Ice Sites, FDD Stations, and Site Median Water Depth

Site No. Name FDD Station Depth (m) 

1 West Tip of Lake Superior Duluth, MN 20 

2 Northern St. Marys River Sault Ste. Marie, MI 1 

3 Straits of Mackinac Alpena, MI 13 

4 Big Bay De Noc Green Bay, WI 2 

5 Little Bay De Noc Green Bay, WI 1 

6 Southern Green Bay Green Bay, WI 3 

7 Saginaw Bay Alpena, MI 4 

8 West Basin Lake Erie Toledo, OH 7 

RESULTS 

The probability of spatial average ice cover falling into one of four ranges (0-25%, 26- 

50%, 51-75%, 76-100%) conditional on a given FDD range is summarized below for 

each site for December and January (Table 2 through Table 17). For example, Table 2, 

for the west tip of Lake Superior, the conditional probability of ice cover in the 0-25% 

range given FDD accumulations at Duluth, Minnesota in the 0-199 range is 100%. 

Supplemental information in the table includes the: 1) average of the spatial average ice 

cover, 2) the average of the FDD, and 3) the number of observations for each spatial ice 

cover and FDD range. For example in the above case where there was a 100% 

conditional probability, the ice cover range for the west tip of Lake Superior is 0-25% 

when the FDD range is 0-199, the average of the spatial average ice cover is 1.2%, the 

average FDD accumulations is 82.9, and there were 17 observations. This supplemental 

information is useful for evaluating the degree of confidence one wants to place in the 
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conditional probability value of ice cover for each table entry. In the above case, one 

would place a high degree of confidence since the number of observations was relatively 

large. However, this is not always the case, e.g., in Table 2, the probability of ice cover 

being between 76% and 100% for FDD between 1000 and 1199 is 71.4%, but this is 

based on only five observations, so that this conditional probability is tenuous. 

 

Graphs of the spatial average ice cover vs. FDDs for each site for December and January 

(Figs. 2-17) supplement the data given in Table 2 through Table 17. The graphs also 

contain a plot (the straight line) of the linear trend in the data. The interval between 

consecutive axis labels on the graph corresponds to the ice cover and FDD ranges in 

Table 2 through Table 17. Thus, these graphs provide additional detail about the 

distribution of the data within each FDD range not given in the Tables. This can be 

important. For example even though Table 16 indicates that there is a 79% probability 

that the spatial average ice cover in western Lake Erie will be between 0% and 25% when 

the FDD at Toledo, Ohio are between 0 and 199, a close look at Figure 16 shows that the 

probability of 0-25% ice cover between 0 and 100 FDD is much higher than is the 

probability for 0-25% ice cover between 100 and 199 FDD. These graphs also show 

where the linear regression model (the straight line) is likely to over-estimate or underestimate the ice cover. 

DISCUSSION 

Highlighted entries in Table 2 through Table 17 show where there is a high conditional 

probability for a given combination of ice cover and FDD ranges. These highlighted 

entries provide a visual aid for the identification of shifts from a high probability of low 

spatial average (≤ 25%) to a high probability of high spatial average (≥ 76%) ice cover 

and for the associated FDD ranges at which they occur. The discussion below briefly 

describes the highlighted entries for each site and related ancillary information. 

Site 1, West Tip of Lake Superior. 

This site is exposed to the open expanse of Lake Superior to the east and to a deep near 

shore trough along the northwest shore. Thus, wind and currents can significantly affect 

the timing of ice formation and movement independent of air temperature trends as 

evidenced by the high frequency of ice cover in the 0 - 25% range for FDDs in the 400-

599 range (Figs 2-3, Tables 2-3). Assel (1991) found that approximately 1300 FDD were 

needed for fall cooling of lake waters in the entire west basin of Lake Superior, mean 

depth 139 m, prior to ice formation in mid-basin areas of that lake. 

The probability of low spatial averaged ice cover (0-25%) is high when FDD < 600 occur 

in both December and January. In December, 67 (17 + 32 + 18) of 97 (17+ 45+ 35) 

observations were in the 0-25% ice cover range (Table 2), in January, 12 (1+11) of 18 

(1+17) were in the 0-25% ice cover range when FDD were < 600 (Table 3). At the other 

extreme there is a high probability of spatial averaged ice cover ≥ 76% in December for 

FDD ≥ 1000 and in January for FDD ≥ 800. 
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Site 2, North St. Marys River. 

This site reacts more rapidly to changes in air temperature than site 1 because of its 

shallower water depth (Table 1). Ice cover is usually ≤ 25% when December FDD is < 

200 (Table 4, Fig. 4). Extensive ice cover forms about 46% of the time when FDD are 

between 200 and 399 (spatial average ice ≥ 76%), but extensive ice cover is more likely 

to occur when FDD are over 400 (84% of the time). This is also true for January (Table 5, 

Fig. 5); spatial average ice ≥ 76% occurs about 58% of the time for FDD between 200 

and 399, 88% of the time when January FDD are between 400 and 599, and virtually all 

the time for FDD ≥ 600. 

Site 3, Straits of Mackinac. 

The Straits of Mackinac area has a median water depth of 13 m. The east-west orientation 

of the Straits provides a fetch limited environment that is favorable for ice formation. The 

probability of ice cover ≤ 25% is 96% for FDD < 200 (Fig. 6, Table 6). The average of 

the spatial average ice cover is 1.8%. This area has a high probability of ice cover ≥ 76% 

in December when FDD are ≥ 400. The same holds true for January. The probability of 

ice cover ≤ 25% is 90% for FDD < 200, (Fig. 7, Table 7), and the average of the spatial 

average ice cover is 5%. At the other extreme, there is a high probability of ice cover ≥

76% in January when FDD are ≥ 400. 

Site 4, Big Bay De Noc. 

This is a shallow, protected site (median depth 2 m) at the northern end of Green Bay. 

There is a 73.8% probability for ice cover ≤ 25% when the FDD accumulation < 200 

(Table 8), although there are a few observations with ice cover ≥ 76% for FDD between 

100 and 200 (Fig. 8). There is a high probability (79% in December, 71% in January) of 

extensive ice cover (average of spatial average > 97%) when FDDs ≥ 200 (Table 8, Table 

9, Figs. 8-9). 

Site 5, Little Bay De Noc. 

This site is similar to Big Bay De Noc, i.e., a very shallow protected site that responds 

rapidly to low FDD accumulations. There is a 77.5% probability for ice cover ≤ 25% 

when FDD is between 0 and 199 (Table 10). However, there is also a 10% chance of ice 

cover ≥ 76% when FDD are between 100 and 199 (Fig. 10). There is high probability 

(66.7% in December, 71.7% in January) of extensive ice cover (average of spatial 

average > 90%) when FDDs ≥ 200 at Green Bay (Table 10, Table 11, Figs. 10-11). 

Site 6, Southern Green Bay. 

Water depths are similar to the two sites at the north end of Green Bay (sites 4 and 5). Air 

temperatures are milder. There is a 78.8% probability for ice cover ≤ 25% when FDD at 

Green Bay, Wisconsin is between 0 and 199 (Table 12) and an almost a 100% chance of 

ice cover ≤ 25% for FDD ≤ 100 (Fig. 12) . There is a relatively high probability (62.5% 

in December, 65% in January) of extensive ice cover (average of spatial average > 90%) 

when FDDs ≥ 200 at Green Bay (Table 12, Table 13, Figs. 12-13). The probability of ice 

cover ≥ 76% increases to 100% (December) and 98.6% (January) for FDD ≥ 400. 
11

Site 7, Saginaw Bay. 

Saginaw Bay has a median depth of 4 m. For December, it can be seen (Fig. 14) that the 

frequency of ice cover < 25% is large for FDD ≤ 100, and the frequency of ice cover ≥

76% becomes large when FDD are between 100 and 200. Saginaw Bay has a high 

probability of ice cover ≥ 76% for FDD ≥ 200 (Table 14). Thus, the transition between 

lower amounts of ice cover and extensive ice cover occurs between 100 and 200 FDD. 

The same pattern holds true for January (Table 15, Fig. 15). 

Site 8, West Lake Erie. 

Western Lake Erie has a median depth of 7 m. In December, there is a high probability 

of low ice cover, ≤ 25%, when FDD are ≤100 (Fig. 16). (This is consistent with Assel 

(1991) who found approximately 50 FDD were associated with fall cooling of west basin 

waters prior to ice formation.) The transition to a probability of higher ice cover, ≥ 76%, 

occurs for FDDs between 100 and 200. Ice cover ≥ 76% is virtually certain for FDD ≥

200 (Table 16). There is a greater probability of ice cover ≥ 76% for FDD < 200 in 

January compared to December and a lower probability of ice cover ≤ 25% (Table 17, 

Fig. 17). The low ice cover for FDD between approximately 300 and 500 in January (Fig. 

17) is due to winters with anomalous declines in ice cover in January (for example: 1974, 

1988, 1990, 1999). Of these winters, 1990 is perhaps most notable. In that winter, (Assel 

and Norton, 1991) an unusually cold December (1989) was followed by a mild January 

(1990) resulting in a large ice loss in Lake Erie in January, preceded by an anomalous 

high ice cover in the last half of December. Never the less there is a high probability of 

high ice cover (≥ 76%) in January for FDD ≥ 200). 

CONCLUDING REMARKS 

If either regression or conditional probability model is to be used in a forecast mode, the 

user (NWS) needs air temperature forecasts in order to calculate FDDs. Monthly air 

temperature forecasts are available from NOAA’s Climate Prediction Center’s Monthly 

and Seasonal Forecasts at: 

http://www.cpc.ncep.noaa.gov/products/forecasts/month_to_season_outlooks.html . 

In any case, the modeled ice cover should be used in conjunction with all other pertinent 

information (e.g., water temperature anomaly, antecedent ice conditions) that is available 

at the time the ice cover outlook is being formulated. As the user becomes familiar with 

these tables, graphs, and regression equations, it is hoped that he / she will gain insight 

and judgment for the appropriate application and interpretation of these data. 

The author wishes to thank Will Kubina at WFO Cleveland for reviewing this report and 

making comments relative to its application in developing improved operational forecast 

of early-winter ice cover. 
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Table 2. Site 1, West Tip of Lake Superior, December FDDs At Duluth MN.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 * * 20.0 45.7 46.7 71.4 100.0 * * * 

51 - 75 * 8.9 8.6 20.0 6.7 14.3 * * * * 

26 - 50 * 20.0 20.0 8.6 * 14.3 * * * * 

 0 - 25 100.0 71.1 51.4 25.7 46.7 * * * * * 

 Average Ice Cover (%) 

76 - 100 * * 89.0 88.4 90.1 94.6 100.0 * * * 

51 - 75 * 56.3 56.0 61.1 58.0 62.0 * * * * 

26 - 50 * 36.2 41.4 41.0 * 38.0 * * * * 

 0 - 25 1.2 8.4 9.2 9.6 10.6 * * * * * 

 Average FDD (o

F) 

76 - 100 * * 498.6 691.1 916.7 1083.4 1220.0 * * * 

51 - 75 * 316.8 571.0 694.0 826.0 1001.0 * * * * 

26 - 50 * 314.4 484.1 673.0 * 1021.0 * * * * 

 0 - 25 82.9 322.3 495.9 723.4 889.7 * * * * * 

 Number of Observations 

76 - 100 * * 7.0 16.0 7.0 5.0 1.0 * * * 

51 - 75 * 4.0 3.0 7.0 1.0 1.0 * * * * 

26 - 50 * 9.0 7.0 3.0 * 1.0 * * * * 

 0 - 25 17.0 32.0 18.0 9.0 7.0 * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 17. 45. 35. 35. 15. 7. 1. 0. 0. 0. 

Figure 2. Site 1, West Tip of Lake Superior, December FDDs At Duluth MN. 
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Table 3. Site 1, West Tip of Lake Superior, January FDDs At Duluth MN.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 * * 5.9 25.7 61.2 69.7 75.0 74.1 84.6 100.0 

51 - 75 * * 5.9 28.6 20.4 7.6 2.3 18.5 7.7 * 

26 - 50 * * 23.5 20.0 6.1 7.6 13.6 7.4 7.7 * 

 0 - 25 * 100.0 64.7 25.7 12.2 15.2 9.1 * * * 

 Average Ice Cover (%) 

76 - 100 * * 98.0 89.0 87.3 94.4 97.6 95.7 99.3 99.6 

51 - 75 * * 64.0 65.1 60.1 67.6 66.0 65.4 55.0 * 

26 - 50 * * 38.8 37.4 35.3 40.6 38.5 41.0 44.0 * 

 0 - 25 * 8.0 8.2 8.7 9.0 11.4 10.3 * * * 

 Average FDD (o

F) 

76 - 100 * * 424.0 741.1 902.7 1103.4 1303.2 1497.5 1671.8 1887.4 

51 - 75 * * 582.0 720.9 869.5 1128.4 1343.0 1514.8 1779.0 * 

26 - 50 * * 491.3 711.0 937.7 1073.0 1307.0 1458.0 1722.0 * 

 0 - 25 * 391.0 506.5 669.2 895.0 1083.5 1267.5 * * * 

 Number of Observations 

76 - 100 * * 1.0 9.0 30.0 46.0 33.0 20.0 11.0 5.0 

51 - 75 * * 1.0 10.0 10.0 5.0 1.0 5.0 1.0 * 

26 - 50 * * 4.0 7.0 3.0 5.0 6.0 2.0 1.0 * 

 0 - 25 * 1.0 11.0 9.0 6.0 10.0 4.0 * * * 

--------------------------------------------------------------------------------------- 

Total No. 0. 1. 17. 35. 49. 66. 44. 27. 13. 5. 

Figure 3 Site 1, West Tip of Lake Superior, January FDDs At Duluth MN.
14

Table 4. Site 2, North St. Marys River, December FDDs at Sault Ste. Marie, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 4.1 46.0 84.2 100.0 100.0 * * * * * 

51 - 75 4.1 26.0 10.5 * * * * * * * 

26 - 50 8.2 4.0 5.3 * * * * * * * 

 0 - 25 83.6 24.0 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 86.7 91.7 94.6 96.1 97.5 * * * * * 

51 - 75 63.0 65.2 60.0 * * * * * * * 

26 - 50 34.3 40.0 45.0 * * * * * * * 

 0 - 25 1.6 5.7 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 151.3 299.2 494.7 658.6 857.0 * * * * * 

51 - 75 103.0 291.6 437.5 * * * * * * * 

26 - 50 83.5 302.0 414.0 * * * * * * * 

 0 - 25 94.7 248.3 * * * * * * * * 

 Number of Observations 

76 - 100 3.0 23.0 16.0 9.0 4.0 * * * * * 

51 - 75 3.0 13.0 2.0 * * * * * * * 

26 - 50 6.0 2.0 1.0 * * * * * * * 

 0 - 25 61.0 12.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 73. 50. 19. 9. 4. 0. 0. 0. 0. 0. 

Figure 4 Site 2, North St. Marys River, December FDDs at Sault Ste. Marie, MI. 
15

Table 5. Site 2, North St. Marys River, January FDDs at Sault Ste. Marie, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 40.0 58.3 88.5 98.6 100.0 100.0 100.0 100.0 * * 

51 - 75 20.0 14.6 9.6 1.4 * * * * * * 

26 - 50 * 12.5 * * * * * * * * 

 0 - 25 40.0 14.6 1.9 * * * * * * * 

 Average Ice Cover (%) 

76 - 100 87.5 91.8 95.9 97.7 98.8 100.0 100.0 100.0 * * 

51 - 75 70.0 64.0 70.0 73.0 * * * * * * 

26 - 50 * 41.7 * * * * * * * * 

 0 - 25 2.5 7.7 5.0 * * * * * * * 

 Average FDD (o

F) 

76 - 100 173.0 338.4 505.6 699.3 896.0 1091.5 1295.2 1511.0 * * 

51 - 75 141.0 337.9 446.4 685.0 * * * * * * 

26 - 50 * 324.8 * * * * * * * * 

 0 - 25 159.0 300.6 439.0 * * * * * * * 

 Number of Observations 

76 - 100 2.0 28.0 46.0 72.0 35.0 30.0 13.0 1.0 * * 

51 - 75 1.0 7.0 5.0 1.0 * * * * * * 

26 - 50 * 6.0 * * * * * * * * 

 0 - 25 2.0 7.0 1.0 * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 5. 48. 52. 73. 35. 30. 13. 1. 0. 0. 

Figure 5 Site 2, North St. Marys River, January FDDs at Sault Ste. Marie, MI. 
16

Table 6. Site 3, Straits of Mackinac, December FDDs at Alpena, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 * 6.7 80.0 100.0 * * * * * * 

51 - 75 1.8 10.0 20.0 * * * * * * * 

26 - 50 1.8 30.0 * * * * * * * * 

 0 - 25 96.4 53.3 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 * 85.0 84.8 96.4 * * * * * * 

51 - 75 55.5 58.7 67.5 * * * * * * * 

26 - 50 41.5 39.7 * * * * * * * * 

 0 - 25 1.8 6.1 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 * 357.0 455.0 659.6 * * * * * * 

51 - 75 187.5 338.7 493.0 * * * * * * * 

26 - 50 169.0 293.1 * * * * * * * * 

 0 - 25 71.8 256.5 * * * * * * * * 

 Number of Observations 

76 - 100 * 2.0 8.0 5.0 * * * * * * 

51 - 75 2.0 3.0 2.0 * * * * * * * 

26 - 50 2.0 9.0 * * * * * * * * 

 0 - 25 106.0 16.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 110. 30. 10. 5. 0. 0. 0. 0. 0. 0. 

Figure 6 Site 3, Straits of Mackinac, December FDDs at Alpena, MI. 
17

Table 7. Site 3, Straits of Mackinac, January FDD at Alpena, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 2.4 42.2 93.8 95.2 100.0 100.0 * * * * 

51 - 75 2.4 16.9 4.6 4.8 * * * * * * 

26 - 50 4.9 15.7 1.5 * * * * * * * 

 0 - 25 90.2 25.3 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 81.0 92.5 93.6 96.7 98.2 100.0 * * * * 

51 - 75 65.0 65.6 72.3 63.5 * * * * * * 

26 - 50 27.5 43.8 40.0 * * * * * * * 

 0 - 25 5.0 10.6 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 197.0 330.2 488.9 717.5 860.1 1086.5 * * * * 

51 - 75 188.0 300.1 520.0 688.5 * * * * * * 

26 - 50 150.0 276.9 525.0 * * * * * * * 

 0 - 25 143.9 254.4 * * * * * * * * 

 Number of Observations 

76 - 100 1.0 35.0 61.0 40.0 24.0 2.0 * * * * 

51 - 75 1.0 14.0 3.0 2.0 * * * * * * 

26 - 50 2.0 13.0 1.0 * * * * * * * 

 0 - 25 37.0 21.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 41. 83. 65. 42. 24. 2. 0. 0. 0. 0. 

Figure 7 Site 3, Straits of Mackinac, January FDDs at Alpena, MI.
18

Table 8. Site 4, Big Bay De Noc, December FDDs at Green Bay WI.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 13.8 79.2 88.2 100.0 100.0 * * * * * 

51 - 75 6.3 8.3 5.9 * * * * * * * 

26 - 50 6.3 4.2 5.9 * * * * * * * 

 0 - 25 73.8 8.3 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 88.5 91.6 97.9 97.9 100.0 * * * * * 

51 - 75 58.2 65.5 60.0 * * * * * * * 

26 - 50 33.8 27.5 40.0 * * * * * * * 

 0 - 25 3.7 6.5 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 159.3 293.8 500.7 683.8 873.0 * * * * * 

51 - 75 127.2 260.5 496.0 * * * * * * * 

26 - 50 145.2 271.5 462.0 * * * * * * * 

 0 - 25 72.2 268.5 * * * * * * * * 

 Number of Observations 

76 - 100 11.0 38.0 15.0 9.0 1.0 * * * * * 

51 - 75 5.0 4.0 1.0 * * * * * * * 

26 - 50 5.0 2.0 1.0 * * * * * * * 

 0 - 25 59.0 4.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 80. 48. 17. 9. 1. 0. 0. 0. 0. 0. 

Figure 8 Site 4, Big Bay De Noc, December FDDs at Green Bay WI.
19

Table 9. Site 4, Big Bay De Noc, January FDDs at Green Bay WI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 33.3 71.7 97.3 100.0 100.0 100.0 100.0 100.0 100.0 * 

51 - 75 22.2 13.3 * * * * * * * * 

26 - 50 33.3 10.0 2.7 * * * * * * * 

 0 - 25 11.1 5.0 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 89.3 97.1 98.4 99.6 99.9 100.0 100.0 100.0 100.0 * 

51 - 75 62.0 59.8 * * * * * * * * 

26 - 50 37.7 36.7 45.0 * * * * * * * 

 0 - 25 3.0 9.7 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 182.3 313.9 504.7 706.2 867.3 1075.6 1285.0 1518.0 1642.0 * 

51 - 75 180.0 294.3 * * * * * * * * 

26 - 50 169.0 318.5 486.5 * * * * * * * 

 0 - 25 127.0 288.3 * * * * * * * * 

 Number of Observations 

76 - 100 3.0 43.0 71.0 50.0 47.0 13.0 3.0 1.0 1.0 * 

51 - 75 2.0 8.0 * * * * * * * * 

26 - 50 3.0 6.0 2.0 * * * * * * * 

 0 - 25 1.0 3.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 9. 60. 73. 50. 47. 13. 3. 1. 1. 0. 

Figure 9 Site 4, Big Bay De Noc, January FDDs at Green Bay WI.
20

Table 10. Site 5, Little Bay De Noc, December FDDs at Green Bay WI.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 11.3 66.7 88.2 100.0 100.0 * * * * * 

51 - 75 5.0 8.3 5.9 * * * * * * * 

26 - 50 6.3 12.5 5.9 * * * * * * * 

 0 - 25 77.5 12.5 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 88.1 91.9 96.3 97.6 100.0 * * * * * 

51 - 75 59.0 64.8 60.0 * * * * * * * 

26 - 50 33.6 34.5 40.0 * * * * * * * 

 0 - 25 4.7 11.5 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 153.7 293.1 500.7 683.8 873.0 * * * * * 

51 - 75 158.3 271.8 496.0 * * * * * * * 

26 - 50 91.6 276.0 462.0 * * * * * * * 

 0 - 25 79.0 283.5 * * * * * * * * 

 Number of Observations 

76 - 100 9.0 32.0 15.0 9.0 1.0 * * * * * 

51 - 75 4.0 4.0 1.0 * * * * * * * 

26 - 50 5.0 6.0 1.0 * * * * * * * 

 0 - 25 62.0 6.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 80. 48. 17. 9. 1. 0. 0. 0. 0. 0. 

Figure 10 Site 5, Little Bay De Noc, December FDDs at Green Bay WI. 
21

Table 11. Site 5, Little Bay De Noc, January FDDs at Green Bay WI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 11.1 71.7 98.6 100.0 100.0 100.0 100.0 100.0 100.0 * 

51 - 75 33.3 11.7 1.4 * * * * * * * 

26 - 50 22.2 11.7 * * * * * * * * 

 0 - 25 33.3 5.0 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 100.0 94.3 97.8 99.3 99.7 100.0 100.0 100.0 100.0 * 

51 - 75 62.0 59.1 70.0 * * * * * * * 

26 - 50 38.0 40.4 * * * * * * * * 

 0 - 25 8.7 10.0 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 169.0 321.1 504.0 706.2 867.3 1075.6 1285.0 1518.0 1642.0 * 

51 - 75 187.3 278.4 521.0 * * * * * * * 

26 - 50 153.5 286.3 * * * * * * * * 

 0 - 25 167.7 288.3 * * * * * * * * 

 Number of Observations 

76 - 100 1.0 43.0 72.0 50.0 47.0 13.0 3.0 1.0 1.0 * 

51 - 75 3.0 7.0 1.0 * * * * * * * 

26 - 50 2.0 7.0 * * * * * * * * 

 0 - 25 3.0 3.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 9. 60. 73. 50. 47. 13. 3. 1. 1. 0. 

Figure 11 Site 5, Little Bay De Noc, January FDDs at Green Bay WI.
22

Table 12. Site 6, South Green Bay, December FDDs at Green Bay, WI.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 7.5 62.5 100.0 100.0 100.0 * * * * * 

51 - 75 6.3 20.8 * * * * * * * * 

26 - 50 7.5 6.3 * * * * * * * * 

 0 - 25 78.8 10.4 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 82.3 90.4 96.5 98.2 100.0 * * * * * 

51 - 75 63.2 67.2 * * * * * * * * 

26 - 50 36.0 41.0 * * * * * * * * 

 0 - 25 2.7 2.6 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 158.5 301.0 498.1 683.8 873.0 * * * * * 

51 - 75 140.0 276.6 * * * * * * * * 

26 - 50 170.0 257.7 * * * * * * * * 

 0 - 25 74.6 250.6 * * * * * * * * 

 Number of Observations 

76 - 100 6.0 30.0 17.0 9.0 1.0 * * * * * 

51 - 75 5.0 10.0 * * * * * * * * 

26 - 50 6.0 3.0 * * * * * * * * 

 0 - 25 63.0 5.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 80. 48. 17. 9. 1. 0. 0. 0. 0. 0. 

Figure 12 Site 6, South Green Bay, December FDDs at Green Bay, WI. 
23

Table 13. Site 6, South Green Bay, January FDDs at Green Bay, WI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 33.3 65.0 98.6 100.0 100.0 100.0 100.0 100.0 100.0 * 

51 - 75 22.2 13.3 1.4 * * * * * * * 

26 - 50 11.1 6.7 * * * * * * * * 

 0 - 25 33.3 15.0 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 90.0 93.2 97.1 99.4 99.0 100.0 100.0 100.0 100.0 * 

51 - 75 71.5 63.6 72.0 * * * * * * * 

26 - 50 36.0 33.5 * * * * * * * * 

 0 - 25 2.3 10.7 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 186.0 321.3 505.3 706.2 867.3 1075.6 1285.0 1518.0 1642.0 * 

51 - 75 176.5 291.8 428.0 * * * * * * * 

26 - 50 180.0 277.0 * * * * * * * * 

 0 - 25 150.0 294.8 * * * * * * * * 

 Number of Observations 

76 - 100 3.0 39.0 72.0 50.0 47.0 13.0 3.0 1.0 1.0 * 

51 - 75 2.0 8.0 1.0 * * * * * * * 

26 - 50 1.0 4.0 * * * * * * * * 

 0 - 25 3.0 9.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 9. 60. 73. 50. 47. 13. 3. 1. 1. 0. 

Figure 13 Site 6, South Green Bay, January FDDs at Green Bay, WI. 
24

Table 14. Site 7, Saginaw Bay, December FDDs at Alpena, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 12.7 83.3 100.0 100.0 * * * * * * 

51 - 75 5.5 6.7 * * * * * * * * 

26 - 50 11.8 * * * * * * * * * 

 0 - 25 70.0 10.0 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 88.6 92.7 97.3 97.0 * * * * * * 

51 - 75 59.0 64.0 * * * * * * * * 

26 - 50 35.8 * * * * * * * * * 

 0 - 25 1.8 14.3 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 147.6 292.7 462.6 659.6 * * * * * * 

51 - 75 129.2 216.0 * * * * * * * * 

26 - 50 140.2 * * * * * * * * * 

 0 - 25 47.6 241.0 * * * * * * * * 

 Number of Observations 

76 - 100 14.0 25.0 10.0 5.0 * * * * * * 

51 - 75 6.0 2.0 * * * * * * * * 

26 - 50 13.0 * * * * * * * * * 

 0 - 25 77.0 3.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 110. 30. 10. 5. 0. 0. 0. 0. 0. 0. 

Figure 14 Site 7, Saginaw Bay, December FDDs at Alpena, MI.
25

Table 15. Site 7, Saginaw Bay, January FDDs at Alpena, MI. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 61.0 86.7 100.0 100.0 100.0 100.0 * * * * 

51 - 75 12.2 8.4 * * * * * * * * 

26 - 50 9.8 1.2 * * * * * * * * 

 0 - 25 17.1 3.6 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 90.7 94.5 97.4 98.5 98.5 100.0 * * * * 

51 - 75 64.0 62.3 * * * * * * * * 

26 - 50 37.3 29.0 * * * * * * * * 

 0 - 25 4.4 4.0 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 155.4 305.4 490.9 716.1 860.1 1086.5 * * * * 

51 - 75 149.6 263.1 * * * * * * * * 

26 - 50 177.8 229.0 * * * * * * * * 

 0 - 25 94.9 214.0 * * * * * * * * 

 Number of Observations 

76 - 100 25.0 72.0 65.0 42.0 24.0 2.0 * * * * 

51 - 75 5.0 7.0 * * * * * * * * 

26 - 50 4.0 1.0 * * * * * * * * 

 0 - 25 7.0 3.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 41. 83. 65. 42. 24. 2. 0. 0. 0. 0. 

Figure 15 Site 7, Saginaw Bay, January FDDs at Alpena, MI.
26

 Table 16. Site 8, West Lake Erie, December FDDs at Toledo, OH.

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 7.5 93.8 100.0 * * * * * * * 

51 - 75 3.7 * * * * * * * * * 

26 - 50 9.7 * * * * * * * * * 

 0 - 25 79.1 6.3 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 88.2 91.8 95.8 * * * * * * * 

51 - 75 60.2 * * * * * * * * * 

26 - 50 35.8 * * * * * * * * * 

 0 - 25 2.9 24.0 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 134.4 278.2 451.6 * * * * * * * 

51 - 75 101.8 * * * * * * * * * 

26 - 50 89.6 * * * * * * * * * 

 0 - 25 24.1 202.0 * * * * * * * * 

 Number of Observations 

76 - 100 10.0 15.0 5.0 * * * * * * * 

51 - 75 5.0 * * * * * * * * * 

26 - 50 13.0 * * * * * * * * * 

 0 - 25 106.0 1.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 134. 16. 5. 0. 0. 0. 0. 0. 0. 0. 

Figure 16 Site 8, West Lake Erie, December FDDs at Toledo, OH.
27

Table 17. Site 8, West Lake Erie, January FDDS at Toledo, OH. 

FDD RANGE 

--------------------------------------------------------------------------------------- 

 0 200 400 600 800 1000 1200 1400 1600 1800 

 199 399 599 799 999 1199 1399 1599 1799 1999 

--------------------------------------------------------------------------------------- 

ICE COVER 

 RANGE 

 Ice Cover Range Probability (%) Contingent on FDD Range 

76 - 100 34.8 78.8 94.2 100.0 100.0 * * * * * 

51 - 75 14.9 11.5 5.8 * * * * * * * 

26 - 50 14.2 3.8 * * * * * * * * 

 0 - 25 36.2 5.8 * * * * * * * * 

 Average Ice Cover (%) 

76 - 100 89.2 93.6 95.2 98.6 99.7 * * * * * 

51 - 75 62.4 67.3 63.3 * * * * * * * 

26 - 50 38.7 41.0 * * * * * * * * 

 0 - 25 8.0 19.0 * * * * * * * * 

 Average FDD (o

F) 

76 - 100 120.9 298.0 473.9 632.3 878.7 * * * * * 

51 - 75 103.0 285.0 438.0 * * * * * * * 

26 - 50 113.7 391.0 * * * * * * * * 

 0 - 25 54.2 384.0 * * * * * * * * 

 Number of Observations 

76 - 100 49.0 41.0 49.0 9.0 3.0 * * * * * 

51 - 75 21.0 6.0 3.0 * * * * * * * 

26 - 50 20.0 2.0 * * * * * * * * 

 0 - 25 51.0 3.0 * * * * * * * * 

--------------------------------------------------------------------------------------- 

Total No. 141. 52. 52. 9. 3. 0. 0. 0. 0. 0. 

Figure 17 Site 8, West Lake Erie, January FDDs at Toledo, OH.
28

REFERENCES 

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

Atlas. NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI, 2 CDROM Set or DVD. (2003). http://www.glerl.noaa.gov/data/ice/atlas/

Assel, R.A., Implications of CO2 global warming on Great Lakes ice cover. Climate 

Change 18:377-395 (1991). 

Assel, R.A., and Norton, D.C., A comparison of Great Lakes winter severity and ice 

cover - winter 1989-90 vs. the historical record. In Proceedings of the 47th Annual 

Meeting of the Eastern Snow Conference, June 7 1990, Bangor, ME. pp. 143-154 (1991). 

Bilello, M. A. Method for predicting river and lake ice formation. J. Appl. Meteorol.

3:38-44. (1964). 

Greene, G.M. Forecasting ice-cover freeze-up, growth, and breakup on the St. Marys 

River. NOAA Technical Memorandum ERL GLERL-47, Great Lakes Environmental 

Research Laboratory (PB83-262097) 82 pp. (1983). 

Meyer P. L. Introductory probability and statistical applications. Addison-Wesley, 

Reading, MA. (1966). 
29

APPENDIX SUMMARY OF REGRESSION ANALYSIS. 

Following is a tabular summary of a linear regression analysis of spatial average ice 

cover for each of the eight ice sites and the FDD stations used for the regressions. Note 

that the regression equations should be used only between the upper and lower bound of 

the FDD values given for each site. For values above the upper limit, the spatial average 

ice cover is assumed to be 100%, for values below the lower limit, the ice cover is 

assumed to be zero in December, and the value it would have had at the lower limit in 

January. 

The regression equation coefficients, B and C in the table below, are artifacts of the 

combination of meteorological station location relative to the ice site and local ice site 

conditions (water depth, water motion [currents, springs, and river outlets], shore 

configuration and topography, and possibly others). The December regression intercept 

term, B, is zero at five of the eight (Straits of Mackinac, Big Bay De Noc, and Little Bay 

De Noc being the exceptions). A zero intercept means that when FDDs are zero, the ice 

cover is also zero. The intercept terms for the January regression equations are not zero 

because there is extensive ice cover at these eight sites during January most winters. The 

fact the January intercept term is > 65 at five of the eight sites indicates that these sites 

usually have an extensive ice cover even in early January for most winters. Exceptions 

occur for the West Tip of Lake Superior, Straits of Mackinac, and West Lake Erie. These 

three sites have deeper waters then the other sites and so contain more heat to retard ice 

formation. The proximity of deeper off-shore waters [and milder air temperatures and the 

Detroit River in the case of west Lake Erie] are contributing factors for observed lower 

intercept term. The other regression equation coefficient, C, in the table below, is a 

measure of the rate of increase in spatial average ice cover relative to the rate of increase 

in FDDs. In December, it is largest for West Lake Erie and smallest for West Superior 

(Fig. A-1). In January, it is largest for Saginaw Bay (West Lake Erie a close second) and 

again smallest for West Lake Superior (Fig. A-2). 

SE = the standard error of estimate, R2 is the square of the variance accounted for by the regression 

equation adjusted for the number of variables in the regression equation. Regression coefficients were 

significant at the 95% confidence level. 

December January 

B C SE R2 FDD Range B C SE R2 FDD Range 

Ice Site 

No. and Name 

FDD 

Station used for 

Regression Analysis 

Ice = B + C x FDD Lower Upper Lower Upper

1. West Superior Duluth 0 0.0711 28.2 0.34 0 1406 17.1 0.04916 28.9 0.24 391 1686 

2. North St. Marys River Sault Ste Marie 0 0.1655 27.9 0.55 0 604 67.1 0.03438 18.1 0.23 141 957 

3. Straits of Mackinac Alpena -8.7 0.1549 14.3 0.74 57 701 17.9 0.1144 25.4 0.53 38 716 

4. Big Bay De Noc Green Bay 12.9 0.1640 29.1 0.54 0 530 76.2 0.02839 16.4 0.17 127 838 

5. Little Bay De Noc Green Bay 10.6 0.1592 28.7 0.53 0 561 72.3 0.03338 16.6 0.22 127 829 

6. Green Bay Green Bay 0 0.1898 26.3 0.61 0 526 67.5 0.03866 19.1 0.22 127 840 

7. Saginaw Bay Alpena 0 0.2281 26.4 0.6 0 438 71.1 0.04147 18.7 0.21 38 696 

8. West Lake Erie Toledo 0 0.2881 19.1 0.71 0 347 40.1 0.1125 27.8 0.38 0 476 
30

Fig A-1. Note that Site 1 (West Tip of Lake Superior) and Site 8 (West Lake Erie) make 

the extremes. Western Lake Erie reacts the most rapidly to increasing FDD 

accumulations and West Tip of Lake Superior reacts the least rapidly to increasing FDD 

accumulations. 
31

Fig. A-2. There is tight packing of the regression lines for sites 2, 4, 5, and 6. Site 1 still 

has the slowest change in ice cover relative to increasing FDDs, but Site 7 now has the 

most rapid reaction to increasing FDDs, with Site 8 virtually the same as Site 7 in rate of 

increase relative to FDD increase.