This is it.
The Dakotas/Nebraska/Oklahoma are Great Plaines, which is culturally distinct. Missouri is southern, although I understand southerners consider them Midwestern. They are a confused state.
Even if you want to argue that, there's no way one can argue that Fargo, Grand Forks and Sioux Falls are Great Plains and not Midwestern. I actually grew up in a rather "confused" city, Bismarck at times feels like the Midwest and at times like the Great Plains. Personally I consider the Bismarck-Mandan metro to be where the Midwest ends, but the influence otherwise is undeniable, Bismarck does unquestionably have a different "feel" than Fargo or St. Cloud. Even Minot I'd put in the same category, but I'd be willing to concede Dickinson. And for South Dakota, Rapid City.
My map is the same plus Missouri, and the string running for the Dakotas to Kansas.