Isle Royale National Park
Michigan, USA
Long-term weather forecast
Long-term weather forecast

Monthly weather forecast and climate
Isle Royale National Park, MI

Calm evening waters at the Rock Harbor in Isle Royale National Park, Michigan
Calm evening waters at the Rock Harbor in Isle Royale National Park, Michigan
Isle Royale National Park has a mild summer humid continental type of climate (Köppen climate classification Dfb) with warm, humid summers and cold, snowy winters. The park includes Isle Royale and hundreds of surrounding islands in the northwest part of Lake Superior in the American state of Michigan. The temperate latitudes and proximity to the abundant water is a significant influence on the climate of the park.

Isle Royale National Park is a remote wilderness with access only by air and water. The largest island is 45 miles long and 9 miles wide at its farthest points. The landscape consists of many ridges that slope gently to the south and steeply to the northern side.
The vegetation consists of spruce, fir, pines, and red cedars along with deciduous trees such as aspen, oak, birch, and maple. The park has a thriving ecosystem of plants and animals.

Summers are warm, humid, and wet in Isle Royale National Park, but the days rarely progress to hot weather. The nights can be cold as the average low temperature during the warmest month of July barely reaches 51.1°F (10.6°C). Winters are cold with the lowest temperatures in January going significantly below the average of -18°F (-27.8°C) during the month. Fog is prevalent in the morning during the majority of the year, which is a navigational risk for ferries and boats. Spring and autumn have mild days with cold nights.

Lake Superior moderates the climate of Isle Royale National Park, yet the annual sunshine registers for 2160 hours. The precipitation is 30" (762mm), which occurs throughout the year, with a peak period during the summer season. Snowfall is heavy during the winter and averages 80" (2032mm) during the year. Prevailing westerly winds average speeds of 15 to 20 miles per hour. Isle Royale National Park reaches frigid temperatures, and the park remains closed during the winter due to the harsh weather.
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The best time to visit Isle Royale National Park is from late spring to early autumn from May to September. The days are warm, while the nights are mild to cold as the park comes to life. The summer has brilliant sunshine and marks the peak of the tourist season. The lake waters are calm, and probably the only time for a comfortable swim is during the warm summer months.

December to February is the worst time to visit Isle Royale National Park and its surroundings in the icy winter. Temperatures drop to extreme lows below -0.9°F (-18.3°C) with heavy snowfall during Christmas and New Year. The thick snowpack hardens on the ground, while the dense fog and strong winds keep the park out of bounds. The park remains closed during the winter from November to mid-April with the freezing of the lake.

Isle Royale National Park is prone to thunderstorms during the summer and snowstorms during the winter. Late spring and summer experience sudden thunderstorms with lightning and heavy rain that can cause discomfort, especially for people who plan to camp during the night. Snowstorms occur regularly during the winter, and there are many instances when a single day accumulates a vast amount of snow. Fog restricts visibility to a few hundred meters during extreme weather.

January is usually the coldest and snowiest month in Isle Royale National Park, with an average low temperature at -0.9°F (-18.3°C). Snowfall is abundant, the lake remains frozen. Weather in January »

February is a cold winter in Isle Royale National Park with average temperatures in the icy zone of 3°F (-16.1°C) to 24.1°F (-4.4°C). The weak sun remains on the horizon for 5 hours a day. Weather in February »

March is windier in Isle Royale National Park as the landscape is still in the grip of the winter. The days are mild and above freezing as the sunlight lasts for a daily 5 hours. Weather in March »

April sees the arrival of the mild spring season in Isle Royale National Park that brings warm days in the region. The average temperatures are in the cold 26.1°F (-3.3°C) to mild 46°F (7.8°C). Weather in April »

The temperatures average in the 36°F (2.2°C) to 57.9°F (14.4°C) as the peak of the spring season is the first time when the night temperatures rise above freezing. Weather in May »

June has the longest days in US National Park Isle Royale, with 9 hours of glorious sunshine. It is a far cry from the harsh winter as the lake and park exhibit many animals, plants, and fish. Weather in June »

July is the warmest and sunniest month of the year in Isle Royale National Park, but the temperatures rarely go above the average high of 72°F (22.2°C). Weather in July »

The average temperatures are in the 51.1°F (10.6°C) to 72°F (22.2°C) zone, but it is rare for days to cross 80.1°F (26.7°C). The lake waters are at their warmest of the year at 55°F (12.8°C). Weather in August »

The beautiful autumn season approaches the region. The lake waters are calm, as the park temperatures average in the 44.1°F (6.7°C) to 63°F (17.2°C) range. Weather in September »

October gets cold during the autumn season in Isle Royale National Park as the first snowflakes register in the region. The landscape is hard, while the lake waters are cold for swimming. Weather in October »

The average temperatures plummet to register in the cold range of 21°F (-6.1°C) to 35.1°F (1.7°C). Heavy fog and strong winds increase the effect of cold in Isle Royale National Park in November. Weather in November »

December is the beginning of the icy winter with substantial snowfall around the island and lake area. The average temperatures are in the bone-chilling 7°F (-13.9°C) to 23°F (-5°C) range. Weather in December »

Months with the highest number of rainy days are June and September (13 days).
Months with the lowest number of rainy days are February and April (8 days).

The best month for swimming (with the highest average sea temperature) is August (55°F).
Coldest months (with the lowest average sea temperature) are January, February, March and April (36°F).