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Climate of the Northern Lake States

Climate refers to the synthesis of day-to-day weather conditions in a given region. Both climate and weather are important for biodiversity because precipitation, temperature, wind, and related environmental conditions affect species over both long term and short term periods.

Regional Climate

The Northern Lake States lie in a humid, continental climatic region with mild to cool summers and generally snowy, cold winters. A rather narrow transition zone extends northwest to southeast from north central Minnesota to southeastern Wisconsin and then east across lower Michigan (Eichenlaub 1979, Stearns 1997). This climatic transition coincides with the "tension zone" (Curtis 1959) between prairie-savanna vegetation to the southwest and northern forests to the north and east.

Upper atmosphere. Weather patterns in the Northern Lake States are influenced by the movement of warm, humid air masses from the Gulf of Mexico and cold, dry air from the Arctic. These air masses generally move from west to east and may shift suddenly in position to create changeable weather conditions.

Additional variations in climate are caused by the Great Lakes themselves. During autumn and winter, Lakes Superior, Michigan, and Huron are rarely covered with ice, and heat stored in the lakes tends to moderate the climate near shores. During spring and summer, the lakes are slower to warm than adjacent land and shoreline areas tend to be cooler than areas farther inland. The cooling effect of the lakes delays the bud and leaf development of plants, minimizing the chances of damage from occasional late frosts. As a result, frost-sensitive plants from warmer climates (e.g., wine-making grapes, apple trees) survive better near the lakes.

In winter, cold air from the Arctic becomes moister while moving over the warmer lakes. When this moist air reaches the lee (usually east) side of the lakes it cools and the moisture condenses, creating "snowbelts" or "lake-effect" snowfalls. In summer, the lakes tend to promote more stable weather in adjacent land areas.

Climatic conditions are important for native plants and animals just as they are critical for farming and other human activities. Regional information about climate as it relates to agriculture is provided by the Wisconsin-Minnesota Cooperative Extension Program and the National Aeronautics and Space Administration (NASA).

Climate Summary (Wisconsin)

(adapted from Climatography of the United States No. 60, NOAA)

The average temperature in Wisconsin ranges from 39 F in the north to about 50 F in the south. The frost-free period ranges from about 80 days in the extreme northwest and north-central lowlands to about 180 days in the southeast. Growing seasons in the central part of the state tend to be shorter than in the Lake Michigan coastal regions and southwestern Wisconsin. The average date of the last spring freeze ranges from early May along Lake Mighican to early June in some of the northern counties. The first freeze during August usually occurs in late August and early September in the north and central lowlands to mid-October along the Lake Michigan coast.

Average precipitation ranges from 30-34 inches annually over the western and northern highlands to about 28 inches along most of the central plain and Lake Superior coastal areas. Higher annual precipitation generally coincides with higher elevation.

Average snowfall ranges from about 30 inches at Beloit (southeastern Wisconsin) to well over 100 inches in northern Iron County. Average annual duration of snow cover ranges from 85 days in southern Wisconsin to more than 140 days along Lake Superior.

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects