According to this Milwaukee Journal Sentinel article, "Wisconsin is at the epicenter of a linguistic collision."

"The unusual vowel sounds are hallmarks of a change coming at us from the Southeast, the so-called Northern Cities Shift in which "aa" and "eh" sounds are being reversed.

This change, however, is moving head-on toward another vowel change coming from the West, the so-called Low-Back Merger. In this second change, words such as caught are being pronounced increasingly like the word cot."