From The weather Vane Wiki
CAD is an acronym term that stands for Cold Air Damming. Cold air damming is shallow cold air being funneled across an area due to topography. The cold air usually travels down the spine of the Appalachian Mountains into upstate South Carolina, then west into northern Georgia and if the "Wedge" is strong enough, sometimes even as far south as northeastern Alabama.
Local Affects from Cold Air Damming
A CAD typically will cause cool rainy conditions with low dewpoints during the early spring and late winter. These CAD's can sometimes inhibit severe weather from affecting CAD prone regions. In the winter a lot of times a strong CAD can cause an ice storm in certain regions, such as Northeast Georgia and upstate South Carolina and western Northern Carolina. CAD's typically or almost always have cool shallow air associated with them, so this shallow layer of cold air is what allows freezing rain to develop.