Just west of Charlotte, and slightly southeast of Asheville, you'll find Rutherford and Polk Counties. In this two-county region, give or take a sliver from surrounding counties, you'll find what's referred to as the "Thermal Belt Region/Zone"
The thermal belt region is an area in NC that will often have a temperature inversion which results in milder temperatures for the thermal belt zone.
It's a region that thrives with a longer growing season, and that has been good news for North Carolina's wine industry and our states apple growers.
The thermal belt phenomenon occurs on the southern slopes of mountains and foothills that are protected from frost and freezing temperatures by higher mountains to the north and northwest. The land can't be flat, and it generally has to be a mountainside for this to form.
Heat is absorbed by the ground during the day, and the heat energy radiates up from the soil at night. As the warm air rises, the radiation of the heat causes the air closest to the ground to cool.
Cold air is heavier than warm air, and this cooler air sinks down the side of the mountain into the valley below. As the cooler/colder air fills the lower valley, this forces the warm valley air upwards.
With a continuous movement of air on the mountain ridge tops, the warm air becomes trapped between the movement of winds above and the cold air filling the valley below. This layer of warmer trapped air is referred to as a thermal belt.
As mentioned above, a longer growing season can be found in these areas that have thermal belt development. Because of the phenomenon, killing frosts are held until later in the fall, and they are generally over earlier in the spring.
Frost can damage grapevines and other plants but with the thermal belt, several rounds of plantings can take place because of the extended growing season.
If you have never been to Polk or Rutherford Counties, there are a large number of wineries in the region; just google! Also, check out the Thermal Belt Rail Trail. It's 13.5 miles of hiking, biking, or walking enjoyment!