While the point of that map is certainly accurate, the numbers are skewed up because of the stations that they are using. Locally, KPDK was +1.8, Fulton County was +1.5, Dallas, GA was +1, and Gainesville was +2.That 3 above in Atlanta is UHI driven for sure. It's surrounded by 1 and 2 above which is really close to average. December felt like a very typical December of my youth.
So basically that map is not all that accurate for our area.