Lake Ice Climatic Atlas for the Great Lakes 1981 to 2010: chapter 2


The Ice Regime

Lake Superior

Ice Regime

Initial ice formation begins in harbours and bays along the north shore, in the western portion of the lake, and over the shallow waters of Whitefish Bay normally near the end of November to early December. The amount and thickness of ice increases so that the entire perimeter of the lake becomes covered and then extends many kilometres out into the lake by mid-winter. At the peak of the season at the last half of February, ice typically covers 75% of the lake. The eastern portion of the lake between Stannard Rock and Caribou Island will usually remain open water throughout the winter.

Break-up normally begins in March and the ice is in a state of deterioration by the end of the month. Most of the lake is open water by mid April; however, winds and water currents can cause the ice to drift into the southeastern end of the lake.

Variations

Ice conditions can vary greatly from year to year. In a mild winter, the maximum ice coverage in Lake Superior may attain only about 12% (1997-98) while during a severe winter coverage may reach 100%. Ice has formed as early as the first week of November and persisted as late as the last week in May.

Ice Thickness

In sheltered harbours and bays, ice tends to grow to 45 to 85 cm during a normal winter. Rafting can create ice thicknesses up to a metre or so. Windrows of grounded ice in Whitefish Bay can pile up to 7-8 metres or more above sea level. Offshore ridges of ice can result in total ice thicknesses reaching 25 metres.

Lake Michigan

Ice Regime

Lake Michigan’s north-south orientation and length mean that it can have ice formation and deterioration occurring simultaneously. Initial ice formation begins in Green Bay normally during the first half of December. The next areas to become ice covered are the Straits of Mackinac and the shallow areas north of Beaver Island. In these areas ice starts to develop in the first week of January. The ice forms and accumulates in a southerly direction with a rapid build-up along the Fox Islands and a slower growth rate around the southern perimeter. Maximum ice cover occurs about the middle of February with usual maximum coverage around 25%. The central portion of the lake south of 45º North latitude usually remains open water throughout the winter.

Break-up normally begins the second half of February and progresses from south to north. Most of the lake is open water by the first half of April. The strait and island areas of Mackinac usually produce formidable ice ridges which linger into late in the season.

Variations

Ice conditions can vary greatly from year to year. In a mild winter, maximum ice coverage in Lake Michigan may be only 12% while during a severe winter it may increase to near 85%. Ice has formed as early as the last week of November and persisted as late as the second week of May.

Ice Thickness

In sheltered harbours and bays, ice typically grows to 45 to 75 cm over winter. Rafting can create ice thicknesses up to a metre or more. Areas of ridges of ice in the Straits of Mackinac can reach up to 9 metres above sea level with depth up to 2 or 3 times greater.

Lake Huron

Ice Regime (Lake Huron and Georgian Bay)

The orientation and patterns of ice formation of Lake Huron are similar to those of Lake Michigan; however, temperature differences between north and south are not as great. Initial ice formation begins in North Channel and along the east coast of Georgian Bay during the second half of December. As the winter progresses, ice expands around the coastal areas and then extends out into the lake. Maximum ice cover occurs around the middle of February with about 50% coverage in Lake Huron and 90% coverage in Georgian Bay. The deep central and north portion of Lake Huron usually remain open water throughout the winter.

Break-up normally begins in March with the entire lake clearing by the second week of April. Large volumes of ice can drift into the southern portion of Lake Huron resulting in a heavy concentration of ice at the entrance to the St. Clair River.

Variation (Lake Huron and Georgian Bay)

Ice conditions can vary greatly from year to year. In a mild winter, the maximum ice coverage on Lake Huron and Georgian Bay may be as low as 26% (winter 2001-02) while during a severe winter, the coverage on Lake Huron and Georgian Bay can be more than 95%. Ice has formed as early as the last week of November and has persisted as late as the third week of May.

Ice Thickness (Lake Huron and Georgian Bay)

In sheltered harbours and bays, lake ice typically grows to 45 to 75 cm during a normal winter. Areas of ridging can contain ice thicknesses of up to 18 metres.

Lake Erie

Ice Regime (Lake Erie and Lake St. Clair)

Ice formation begins in the western end of the lake and in Long Point Bay normally during the second week of December. Elsewhere the amount of ice cover begins to accelerate in early January and is usually at its maximum extent (70%) in February. Lake St. Clair is normally completely ice covered or consolidated from the middle of January until March.

Break-up for Lake Erie normally begins near the end of February with the lake becoming mostly open water by the first week of April. The eastern end of the lake is usually the last area to clear.

Variations (Lake Erie and Lake St. Clair)

In a mild year, the maximum extent of the ice cover could be as little as 8% of the lake's surface. During severe winters, 100% coverage can occur. Ice has formed as early as the first week of December and has persisted in the Buffalo area as late as the middle of May.

Ice Thickness (Lake Erie and Lake St. Clair)

In sheltered bays, ice typically grows to 25 to 45 cm over winter. Rafting and ridging of ice can create aggregate ice thicknesses in excess of 20 metres during a single winter storm.

Lake Ontario

Ice Regime

Ice formation begins in the Bay of Quinte normally during the third week of December. Ice begins to form in the bays at the eastern end of the lake and in the approaches to the St. Lawrence River during the first week of January. An extensive ice cover does not appear until the last week of January and is usually confined to the eastern end of the lake. Maximum ice cover which usually occurs during the first half of February totals about 17%.

Break-up normally starts late in February with the lake becoming generally open water in late March. Ice may be found below Niagara Falls, in protected bays and in the approach to the St. Lawrence River somewhat later.

Variation

In a mild winter, ice coverage on Lake Ontario is only about 10% while in a severe winter it can increase to 65%. Lake Ontario will rarely reach complete ice cover; one year this happened was in 1979. . Ice has formed as early as the third week of November and has persisted as late as the last week of April.

Ice Thickness

In the sheltered bays, ice typically grows to 20 to 60 cm over winter. Ridging, rafting and hummocking can significantly increase these thicknesses.

Variability of Total Ice Coverage

In this atlas, there is a new parameter that depicts an entire ice season as a single value known as “Total Accumulated Coverage (TAC)”.This parameter permits comparisons of one season to another.

In order to calculate the TAC, each polygon area is multiplied by the associated total ice concentration, summed up for the entire chart, and then normalized by the total area to arrive at a single value for each chart.  This value is then summed for the entire season and finally normalized by the number of weeks in a season to arrive at the single value for the season. 

The most ice encountered in a single season in the Great Lakes for the period occurred in 1993/94 and represents (on average) approximately 28% ice coverage throughout the entire season; the least amount of ice occurred in 1997/98 and represents approximately 3% ice coverage; and the median amount of ice is approximately 13% ice coverage. From 1981 to 2010 there was no statistically significant trend in the amount of ice coverage.

The most ice encountered in a single season in Lake Ontario for the period occurred in 1981/82 and represents (on average) approximately 12% ice coverage throughout the entire season; the least amount of ice occurred in 2001/02 and represents near 0% ice coverage; and the median amount of ice was approximately 4% ice coverage.

The most ice encountered in a single season in Lake Erie for the period occurred in 1981/82 and represents (on average) approximately 39% ice coverage throughout the entire season; the least amount of ice occurred in 1997/98 and represents near 0% ice coverage; and the median amount of ice was approximately 21% ice coverage.

The most ice encountered in a single season in Lake Huron for the period occurred in 1993/94 and represents (on average) approximately 35% ice coverage throughout the entire season; the least amount of ice occurred in 1997/98 and represents approximately 7% ice coverage; and the median amount of ice was approximately 18% ice coverage.

The most ice encountered in a single season in Lake Michigan for the period occurred in 1993/94 and represents (on average) approximately 17% ice coverage throughout the entire season; the least amount of ice occurred in 1997/98 and represents approximately 3% ice coverage; and the median amount of ice was approximately 8% ice coverage.

The most ice encountered in a single season in Lake Superior for the period occurred in 1995/96 and represents (on average) approximately 33% ice coverage throughout the entire season; the least amount of ice occurred in 1997/98 and represents approximately 2% ice coverage; and the median amount of ice was approximately 14% ice coverage.

Examples of minimum and maximum ice conditions for the entire Great Lakes region are provided to illustrate the spatial extent of such ice conditions

Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: