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Average daytime high temperatures range from 60 degrees Fahrenheit in May, to the upper 80s in mid-summer, to the mid-60s in September. Average lows vary from 40 degrees in May, to the upper 50s in mid-summer, to 50 degrees in September. Average water temperatures in May and June are only in the 40s. Even in late summer, surface temperatures rarely exceed 60 degrees, except in protected bays. Average summer winds blow at from 5 to 20 knots with waves of from one to four feet. Winds of 30 to 40 knots and 6 to 12 foot seas are possible.
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The Apostle Islands National Lakeshore is open year round, however accessing the islands during the winter months can pose many challenges and is not very common due to unstable lake conditions. Average temperatures during the winter range from 20ºF to 6ºF and into the negatives depending on wind chill. Average snowfall is around 99 inches a year. Be sure to check the Current Conditions in the park before you visit.
Last updated: April 1, 2021