There are a few ways to classify climates. The plant hardiness zones often published with seed packages are one way to group climates. That approach is based on minimum wintertime temperatures but is limited in its usefulness because a good climate map should include reference to more than one weather variable.
Between 1918 and 1936 Vladimir Köppen (pronounced KEPP-in) devised the climate classification scheme that is most widely used today. He used vegetation and temperature as natural indications of the climate of a region. Climate scientists have made improvements to the original Köppen scheme, most recently in 2007; it is now called the Köppen-Geiger map.
The current Köppen-Geiger classification scheme has five main groups, each designated with a letter: Tropical Moist (A), Dry (B), Moist with Mild Winters (C), Moist with Severe Winters (D) and Polar (E).
Some groups are described by two- and three-letter designations. The second letter usually refers to whether and when a dry season occurs, and the third letter denotes differences in temperatures. The dominant climate classification over land is arid B (about 30 percent) followed by cold D (about 25 percent) and tropical A (19 percent). The moist and mild C climate only occupies about 13 percent, about the same as polar E zones. Following this major classification, denoted by a capital letter, is a second letter that is not capitalized that usually refers to whether and when a dry season occurs.
Wisconsin is a “Df” climate type. The “D” part of this classification means the climate includes variable weather patterns with a large variation in seasonal temperatures. The average temperature of the coldest month is less than 32 degrees F, and the warmest month has an average temperature exceeding 50 degrees. These climate types usually have snow on the ground for extended periods. The “f” designation indicates that there is no dry season.