Rob Mifsud wrote a nice, readable explanation of the Northern Cities vowel shift that’s happening in the United States:
American dialects are actually diverging.
There are multiple examples of such divergence. But none is as dramatic, as baffling to linguists, and as mysteriously under the collective radar as what’s happening in the cities that ring the Great Lakes. From Syracuse, N.Y., in the east to Milwaukee in the west, 34 million Americans are revolutionizing the sound of English.
Language is weird and fascinating.