Michigan has a temperate climate with well-defined seasons. The warmest temperatures and longest frost-free period are found most generally in the southern part of the lower peninsula; Detroit has a normal daily mean temperature of 49°F (9°C), ranging from 23°F (–5°C) in January to 72°F (22°C) in July. Colder temperatures and a shorter growing season prevail in the more northerly regions; Sault Ste. Marie has a normal daily mean of 40°F (4°C), ranging from 13°F (–11°C) in January to 64°F (18°C) in July. The coldest temperature ever recorded in the state is –51°F (–46°C), registered at Vanderbilt on 9 February 1934; the all-time high of 112°F (44°C) was recorded at Mio on 13 July 1936. Both sites are located in the interior of the lower peninsula, away from the moderating influence of the Great Lakes.

Detroit had an average annual precipitation (1971–2000) of 32.9 in (83.6 cm). The greatest snowfall is found in the extreme northern areas, where cloud cover created by cold air blowing over the warmer Lake Superior waters causes frequent heavy snow along the northern coast; Houghton and Calumet, on the Keweenaw Peninsula, average 183 in (465 cm) of snow a year, more than any other area in the state. Similarly, Lake Michigan's water temperatures create a snow belt along the west coast of the lower peninsula.

Cloudy days are more common in Michigan than in most states, in part because of the condensation of water vapor from the Great Lakes. Detroit has sunshine, on average, only 32% of the days in December and January, and only 49% year-round. The annual average relative humidity at Detroit is 81% at 7 AM, dropping to 60% at 1 PM; at Sault Ste. Marie, the comparable percentages are 85% and 67%, respectively. The southern half of the lower peninsula is an area of heavy thunderstorm activity. Late spring and early summer are the height of the tornado season.