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.

Current Weather in the Isle Royale Region

Averages and Records at Isle Royale

Month	Avg High	Avg Low	Record High	Record Low	Avg Precip
January	19	-3	48	-39	2.58
February	24	2	55	-43	1.41
March	35	14	63	-25	1.56
April	47	27	82	-4	1.84
May	61	38	88	22	2.50
June	69	46	95	28	2.58
July	75	51	94	38	2.49
August	73	52	94	34	2.41
September	64	43	86	24	3.45
October	52	34	78	13	2.99
November	37	20	71	-17	2.13
December	24	4	52	-28	1.89

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