My Big Fat Northern Cities Vowel Shift

Watched My Big Fat Greek Wedding last night, and a great thing about it is that it's a Chicago movie where most side characters actually sound like they're from Chicago. Too many 'Chicago' movies/TV shows have characters say things like, "Mawm and Dahd drove bahck from Rawkford." Gimme those nasally vowels!

P.S. What Chicago accent?? From Slate: