What thickness of OSB board should be used on a roof in Tennessee?

Our house currently has 7/16 inch OSB on it. We are going to replace the shingles, and my father-in-law (who lives in Minnesota) says that we should have 5/8 inch. Upon talking to some other people who have had their roofs done in the area, they say that they think 7/16 inch is standard for Tennessee. Anyone have any expert advice in the area?