The Artic gyre is now stronger than ever, the Rocky Mountains still loom high in the west, and blasts of below zero F temps should be suspected and braced for through mid February. The real cold weather often doesn't really arrive until weeks after the winter solstice. So a good quality parka could yet turn out to be a good investment. I've longed for mild winters like that of 1998 for 20 years, and I have been regularly disappointed.
Recently deep cold in southern WI seems to come in shorter outbreaks, 1-3 days in duration, pushed by dips in the arctic gyre that haven't been stalled by extended Omega blocks (I expect that's subject to variability, and also undependable). These deep freeze episodes seem to come rather regularly, maybe 3-5 weeks apart. Across winter and spring there is often cold looming in the near term future.
So, I say enjoy the mild weather but keep that good winter coat and the double lined gloves/mittens handy, especially if you ride public transit and need to stand at bus-stops and train platforms.