It turns out I'm still right about two things I said yesterday: First, yesterday did set the record in Chicago for the coldest January 1st on record when the temperature only managed to get up to -17°C. (The previous low-maximum record was -15°C set in 1969.)
Second, last night's overnight minimum temperature was a full half-degree C warmer than the overnight low on January 1st. So far, then, January 1st is still the coldest day of 2018.
That said, I did not enjoy my commute this morning.