I bought some ankle booties to potentially wear, although my pumps are so comfortable (
Michael Kors Dorothy flex pump, literally cannot recommend these enough) my plan is to wear these exclusively onsite. Depending on the weather, I might wear ankle booties to the interview and then change into my pumps once inside. I was in both the Northeast and Midwest earlier this week and there was snow on the ground but not on the sidewalks or road so I haven't yet had an issue. As a fellow Southern gal, I know the struggle!
edit: I should also add, the ankle booties I bought were by no means "winter boots." They were just more sturdy and warmer than a pump haha