We've been several times in January. The crowds are definitely quiet, just avoid President's Weekend as that one usually attracts bigger crowds. But still much, much better compared to summer season, Christmas, Spring, Break, etc. The weather is a difficult variable to predict. One year, it was shorts the entire time, 70+, beautiful. The next, winter clothes. Average experience has been cool in the mornings and evenings and warmer during the day. So you just have to watch the weather reports before you go and plan to bring lots of layers.