Pretty pitiful that Atlanta couldn't manage to get below 37 the last 2 mornings. I guess the heat island only applies to Atlanta and not Nashville, Charlotte, or Raleigh.
With the airport sitting on a ridge at around 1000', completely surrounded by three large interstates, and being so close to the main part of the city, the UBI effect is just that more exponential. Lower areas that are farther out like La Grange and Newnan area always colder at night. The coldest I got was 34F at 1140' when all the lower areas a hundred or two feet lower hit freezing. I was driving back through western North Carolina last night and when I was going over a ridge top the temp was at least 5 degrees warmer than the valleys.