Which states qualify as culturally Southern?

[Orser67]

If you're along or south of U.S. 60, you're in the South, period. If you're along or north of U.S. 50, you're NOT in the South, period. Between U.S. 50 and U.S. 60 is where the North and the South blend, with the culture becoming more Southern closer to U.S. 60, and more Northern closer to U.S. 50. This rule applies as far west as the 96th meridian. Nowhere west of the 96th meridian is in the South.

This seems like a pretty solid definition of the South.