The temperature finally got down to freezing at O'Hare, which is the latest freeze recorded there since records started in 1958:
With widespread freezing temperatures across the Chicago metro area, Friday's official low temperature reading at the O'Hare observation site should bottom out well below 0°C --- marking the first time readings there have dropped below that mark since April 1st. It also marks the latest in the season the first 0°C temperature has been observed at that site since it was established in 1959.
(Tom Skilling errs in two places here. First, the O'Hare site opened on 1 November 1958; second, while he's correct that the temperature last dropped below 0°C on April 1st, it only reached 0°C last night.)
The forecast calls for temperatures as high as 16°C this weekend, followed by...winter.