A useful page
If you follow the links in this web page
you will get to a calculator which will give you a more accurate hardiness zone for your site, compared to the 2012 USDA map.
I, for example, am warmer by 2.6 F compared to the USDA map, and of course my observations tend to agree with that assessment. Add a little heat due to buildings, and voila', it' s asian persimmons next year.