I know of pool owners in central and eastern North Carolina that keep their pools open, but I believe you are in a colder part of the state.
This link shows maps of normal daily minimum temperatures for each month in North Carolina. I'm assuming that the "foothills" region you are referring to is in the western part of the state where it looks like January and February are the coldest months with temperatures below freezing in the 20-25 and 25-30 range depending on where you live. These are averages so particular days (nights) could be far colder. I'm going to guess that it would be difficult to keep it open through the coldest part of the winter, but the best way to know for sure is to talk to others in the same area to see what they do. The day temperatures (see
this link) are generally above freezing so technically if you ran the circulation pump at night you would probably prevent freezing, but if the power went out for any reason (and winter storms sometimes knock out power) and it was a particularly cold night, you'd be in real trouble.