Not all of these characteristics are unique to the North Central region.
Vowels
Monopthongization occurs in words such as boat, so, etc. such that /oʊ/ is often pronounced as a nearly pure close-mid back rounded vowel [o]. Monopthongization also occurs in /eɪ/, bringing its pronunciation closer to a pure [e] in words such as day, play, etc.
The words roof and root may be variously pronounced with either /ʊ/ or /u/; that is, with the vowel of foot or boot, respectively. This is highly variable, however, and these words are pronounced both ways in other parts of the country.
The Mary-marry-merry merger: Words containing /æ/, /ɛ/, or /eɪ/ before an "r" and a vowel are all pronounced "/eɪ/-r-vowel," so that Mary, marry, and merry all rhyme with each other, and have the same first vowel as Sharon, Sarah, and bearing. This merger is widespread throughout the Midwest, West, and Canada.
The words cot and caught are distinct in some areas of this region, and are the same in other parts; see cot-caught merger for more information.
For some people, /æ/ merges with /eɪ/ before /g/, so that flag rhymes with plague; both words are pronounced with the vowel sound of the word face. Even in speakers that do not have the merger, there is noticeable raising of /æ/ before g, such that bag and bat have different vowel sounds.
Canadian raising can be found in the speech of some people in this area. This means that the word like can have a different diphthong than the word line, and (although less commonly in this region) about can have a different diphthong than the word loud. The former offers distinction between the pronunciation of "writer" and "rider," as well as between "hire" and "higher."
The Northern cities vowel shift has an influence over much of this region. Accents in which /ʌ/ is more retracted than /ɑ/ (whether by backing of /ʌ/, fronting of /ɑ/, or both) can be found in southeastern North Dakota, northeastern South Dakota, much of northern Iowa, much of Minnesota, and the vast majority (if not all) of Wisconsin. The diphthongization of /æ/ before oral consonants is found in parts of Minnesota (St. James to the south, Minneapolis-St. Paul, and Brainerd to the north). Indeed, Labov et al. introduced a narrower definition of the "North Central" region as a residual region distinct from both the West and the North, thus excluding the area affected by the Northern Cities Shift.
The conservative character of the region is best exemplified by the speakers of northern Iowa, who come as close to Labov's initial position as any in the country. The more northerly parts of this region show the well-known monophthongal character of the long high and mid vowels. The stereotype of Minnesota speech, for example, is expressed in the pronunciation of Minnesota with a long, monophthongal o: [ˌmɪnəˈsoːɾə].
