Riding 100 km during these cold days is a huge achievment, at least for me! I regularly ride 200 to 300 km a day during the long and warm summer days, but when the weather gets cold and rainy, its another story. I seldom find enough will to ride 100 km in december.
Don't worry too much about hand numbness: its always worse during cold weather, and its often problematic during your first long rides. Combining both factors is asking for trouble!