Maybe it is hard to find inspiration? And it's easy to slip into a pattern of staying indoors, cranking up the heating, sitting in front of a warm fire and turning on the TV. Wrap up, drink wine and hibernate (which is pleasant for a while).
But there is something envigorating about the morning frosts and icy breezes. It wakes you up and feeds creativity.
So, get outside, take a pad and pencil (or phone) and experience the cold. Write about how that makes you feel. Go somewhere wild and look at the light - December's low sun makes for fabulous shadows.
And once you'd written something (and got cold enough). Use the long, dark nights to redraft your material. Make winter your best season for writing.