Lake Superior greatly moderates temperature extremes, slowing spring warming as well as delaying the onset of winter. The coldest months average well below 32°F (0°C) and the warmer months average about 70°F (22°C).
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 at the lakeshore. Annual precipitation averages 31 inches; annual average snowfall ranges from 140 to 160 inches with some years over 200 inches. Snow generally covers the ground from late November through late April.
The area is 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 often results in rain, fog, and snow. Spring is relatively clear due the cold water surface of the lake.
The prevailing wind is from the west, with average velocities ranging from 7 to 9 miles per hour. High winds and storm conditions on Lake Superior are not uncommon. In summer, temperatures can vary dramatically throughout the day when northwest winds (off the cool lake) switch back and forth with southwest winds (off the warm land).
The lakeshore is located approximately 46 degrees north latitude and 86 degrees west longitude.