About Isle Royale Weather

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 52F. 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.



Month Avg High Avg Low Record High Record Low Avg Pcpt
January 19-348/2003-39/19961.33"
February 24255/1991-43/19960.80"
March 351463/2003-25/19891.55"
April 472782/1965-4/19952.22"
May 613888/197722/19892.86"
June 694695/199528/19983.19"
July 755194/196638/19683.45"
August 735294/200134/19763.10"
September 644386/197824/19653.68"
October 523478/200313/19763.25"
November 372071/1999-17/19762.37"
December 24452/1962-28/19671.56"
Disclaimer about the stats


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