My furnace has reached the limits of its ability to keep my apartment warm as the delta between inside and outside temperatures has hovered around Δ40°C for 48 hours now. Even though the temperature has started going up, and will continue to do so until hitting the nearly-tropical 10°C by mid-day Sunday, the outside air still hurts my face.
Yesterday's official high was -23.3°C, and the low was -30.6°C. So we missed setting the all-time record cold high by Δ0.6°C, and we're a few degrees from the all-time record cold low set 20 January 1985. Overall, yesterday was the 5th-coldest day in Chicago history.
Here are the temperatures since noon Wednesday (with room for the chart to grow through the weekend):

Compare that with the last polar vortex in January 2014. This one is colder but shorter, and will have a much warmer denouement. And if we get up to 10°C, the Δ42.8°C warm-up will break the all-time warm-up record set from 25-29 December 1984 (Δ40°C).
I recommend listening to Brendel and Fischer-Dieskau performing Schubert's "Winterreise" while you absorb these other facts:
- Officials in the Midwest blame only six deaths on the record cold, which speaks to the seriousness with which people are taking this crap.
- With particular derision directed at the President, this cold snap barely registers globally as scientists report that 2018 was the 4th-hottest year in recorded history—after 2015, 2016, and 2017.
I'm looking forward to the warm-up, even though its leading edge brings some snow with it.