The New USDA Hardiness Zone Map Is Here
The looooooooooooong awaited new official USDA hardiness zone map is here! Looks like most of Tennessee is now officially rated as 7a and there's a range from 6a (only some really small pockets) to 8a (right around Memphis). I think the way they've used the data may represent a very conservative representation (showing ratings lower than what most of us would consider accurate), but it's still hopefully much more useful than the old map.
Here is a link that might be useful: New USDA Plant Hardiness Zone Map