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Weather in Isle Royale

Isle Royale National Park is the only national park that is closed in the off season. This is due to bitterly cold weather experienced outside of the summer. Lake Superior weather is cool even in summer, causing often dense fog. The lake’s water temperature rarely exceeds 52°F. Thunderstorms and rain occur throughout the summer, causing frequent and major changes in wind. Because of this, rough seas can be an issue on Lake Superior at any time. The statistics below are taken from the town of Grand Portage, Minnesota, the closest area on the mainland to the park.

Averages and Records at Isle Royale

MonthAvg HighAvg LowRecord HighRecord LowAvg Precip
January19-348-392.58
February24255-431.41
March351463-251.56
April472782-41.84
May613888222.50
June694695282.58
July755194382.49
August735294342.41
September644386243.45
October523478132.99
November372071-172.13
December24452-281.89

All temperatures are reported in Fahrenheit. All precipitation is reported in inches.

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