It turns out, I only got half the story about today's weather. The 13.3°C figure is only the high maximum record for O'Hare, whose records only go back to November 1958. But the official record for Chicago goes back to 1871. The offical record high maximum was 17.1°C, set in 1876. O'Hare didn't break that record today, but Midway—where our official weather station was from the 1930s until 1958—might have tied it.
We might, however, get the high minimum temperature tonight. That record, 6.1°C, has lasted since 1886. Last evening's low was 8.9°C, around what tonight's forecast calls for.