Emily Badger for The Atlantic:

Sometime around the 1960s and ’70s, people in Philadelphia began slowly, subtly to change how they speak. The sound of their vowels started a gradual shift consciously imperceptible to the very people who were driving it. A’s evolved to bump into E’s. The sound of an O lost some of its singsong twang. After decades of speaking with what was in effect a southern dialect, Philadelphians were becoming – linguistically, that is – more northern.

Fascinating piece, and helps explain why my Linguistics professor and teaching assistants back in college loved hearing my accent and encouraged me to write about it.