I ran an analysis of the growing degree day accumulation for Auburn, AL for this year and 2015 up until February 6. I used a 0 degree base temperature to keep it simple. The figure inset is very telling of what has occurred– basically over the first ~35 days of the year the number of growing degree days in 2017 is almost double 2015 with approximately 450 accumulating in 2017 and 250 in 2015. Basically the two weeks in January of warm-weather experienced across the US are the cause for the high accumulation up to this point.
Here is one last thing to think about — what if we experience a two to three cold period or if we dip below freezing? Does that mean all growing degree days should reset? Even worse, what if we do not dip below freezing again? Does this mean we should not reset and we should count all growing degree days since January 1? This is why, in my opinion, that accumulation of growing degree days starting January 1 in the Southeastern US and other similar regions might need to be rethough.