Could be 85 for a high, could be 45 for a high, could be both in the same week! We have been in December several times, and we learned that you have to pack to be prepared for everything. The weather changes fast, and you can't trust the weather predictions. I'm pretty sure January is about the same. In December, we have spent part of the week in t-shirts and shorts day and night, and another part of the same week in heavy coats and gloves. It is very unpredictable. We do enjoy the fact that it isn't sweltering hot every day!