I looked up averages for Green Bay, I am south of that and the other Wisconsin based poster is north of that, for January the averages are -4C as a HIGH and -13C as a low that is average keeping in mind here January is the coldest month because we have winter at the right time of year.
Far as...
I presume when you are saying sub-zero you mean Celcius, stateside we use Fahrenheit. I live in Wisconsin like blucoondawg but I believe a bit further south, -25C happens just about every single winter and I have seen -32C, we can have a week at a time where the highs are -13C.
In a car it is...