Chill hours are basically accumulations of the time that an area experiences a temperature below 45 degrees F, although there are several variations on this basic idea. Fruit trees need a certain amount of cold weather while they are dormant to set a good crop of fruit for the next growing season. This year, because of the warm December, chill hours have been lagging. This has been a worry for the farmers who need good yields to pay the bills. The cold outbreak we had late in the month really helped farmers catch up on lagging chill hour accumulations.
The graph below shows the chill hour accumulation for Tifton GA using the Agroclimate web site from the University of Florida. Note that not many chill hours accumulated in the first half of December but that there was a sharp increase in the total after that. The area in blue shading shows the range of possible accumulations based on previous La Nina winters. Since the next two weeks should be fairly warm, the curve is likely to follow the low end of that blue shading, but cooler temperatures are expected to return by mid-January, although they will not be as cold as during the outbreak.
I spoke to a blueberry producer down in South Georgia today, and he tells me that Southern Highbush blueberries already have nearly enough chill hours to bloom in spring when the first warm spell occurs, although the rabbit-eyes are farther behind and could use some more cold. That could be a problem if we go back into a pattern of colder conditions after that, but it is too far out to predict at this point. Note that it is hard to get to the level of the historic average now because winters have been getting warmer, reducing the number of hours below 45 F.