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Summer Weather

Lake Superior is renowned for its cold temperatures, rough seas, fog, and sudden squalls. Boaters and paddlers should monitor marine weather forecasts, check the WISC-Watch buoy network, and be constantly alert to changing conditions.

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.

We do not recommend any travel on Lake Superior during Small Craft Advisories or Gale Warnings. A Small Craft Advisory is issued by the National Weather Service when sustained winds or frequent gusts are between 22 and 33 knots (25 and 38 mph) inclusive, and/or waves are greater than 4 feet. A Gale Warning is issued when sustained surface winds, or frequent gusts, in the range of 34 knots (39 mph) to 47 knots (54 mph) inclusive, are predicted or occurring.

As you prepare for your trip, it never hurts to plan for an unexpected weather delay, monitor weather forecasts, and be alert to changing conditions.

Check for an up-to-date weather on Lake Superior:

A color coded wind chill chart with wind speed, temperature, and wind chill in Fahrenheit.


Winter Weather

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.

There is limited outdoor recreation during the winter. The trail head for the Lakeshore Trail located on the mainland unit at Meyers Beach is a common place to hike and snowshoe during the winter.

Not every year, but when the weather conditions are just right there is a possibilty of ice cave formations at the mainland sea caves. As ice starts forming on Lake Superior, waves splash against the rock and began to freeze on the sandstone cliffs. Water seeps between sandstone rock layers and freezes forming a variety of features similar to limestone caves. There can be large icicles and formations hanging off of the cliffs, curtains and columns of ice, and abundant ice crystals.

Ice is never considered completely safe. Ice conditions can change rapidly, so keep safety in mind at all times. Park staff monitor ice conditions at the Mainland Ice Caves to determine when the ice is Low Risk enough for visitor traffic. Temperature, high wind speeds and direction can quickly change ice conditions. Images of the ice conditions at the caves can be found on the sea caves watch website. Satellite imagery of ice cover on Lake Superior can be found on NOAA's CoastWatch-Great Lakes Region website.

Be prepared for any winter visit. Make sure to bundle up and dress in layers. Take something that will allow you to cover your face – a neck gaiter, balaclava, or scarf. Bring water and a snack. Pay attention to weather and wind chill factor. The caves are very exposed to wind, especially from the west. Spiked footwear, such as Stabilicers or Yaktrax, is highly recommended. The entire area tends to be very slippery. You may encounter slush or wet areas. Wear waterproof boots with non-skid soles and cleats. Tennis shoes are not recommended.

A rocky cliff covered in ice and snow near a lake with large chunks of ice floating.
Ice conditions are variable and subject to change on a daily basis during the winter. Please use caution when visiting the park this time of year!

NPS Photo/ N. Howk

A graphic with the words "Ambassador, WRN, Weather-Ready Nation".

Graphic / NOAA

We're pleased to join our partners at the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service (NWS) as a Weather-Ready Nation Ambassador. We regularly utilize the NWS Apostle Islands Marine Forecasts as we plan our work. We encourage anyone traveling on the lake to check those forecasts early and often throughout a trip, to avoid being surprised by sudden changes in Lake Superior weather.

Last updated: February 22, 2022

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415 Washington Avenue
Bayfield, WI 54814


715 779-3397

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