Lars Jensen photo
Lake Superior greatly ameliorates temperature extremes, slowing spring warming and the onset of winter. The average date of the last freezing temperature in spring is June 8, and the average first fall freeze is September 23; however, freezing can occur during any month. The freeze-free period, or growing season, averages 107 days annually.
The big lake's presence also increases precipitation in the lakeshore. Annual precipitation averages 79 cm (31 inches); annual snowfall is 320 cm (126 inches). Snow generally covers the ground from late November through late April.
The area is within the second-most cloudy region of the United States, characterized by an annual mean cloud cover of 70 percent. Much of the cloudiness occurs in autumn and winter and can be attributed to cool air flowing over Lake Superior being warmed along the shore and forming clouds. This condition also often results in rain, fog, and snow. Spring is relatively clear due to the cold water surface of the lake.
The prevailing wind is from the west, with average velocities ranging from 12 to 15 kilometers per hour (7 to 9 mph). High winds and storm conditions on Lake Superior are not uncommon. The highest recorded one-minute wind speed is 98 kilometers per hour (59 mph).
For more information
Climate Change (website)
Climate Change in National Parks (pdf)
Climate Change and the Great Lakes (pdf)
National Park Service Climate Friendly Parks (website)
National Park Service Great Lakes Inventory and Monitoring Network (website)
National Weather Service Forecast Office, Marquette, Michigan (website)
Did You Know?
Several species of plants in the Buttercup Family are aquatic, growing underwater in lakes and ponds. A few are even amphibious, meaning that a single plant lives partly on sand along a shoreline and partly submerged. Such plants have runners, like a strawberry plant, and grow roots along the runners. The submerged leaves appear quite different from the ones growing in air.