It happened around Labor Day weekend, the spiritual end of Midwestern summer. School was about to go back in session and those waking up early found that it was no longer sunny and sweltering at 7 a.m. While there were still several weeks left before autumn, there was a creeping cold in the upper Midwest over the holiday weekend, a reminder to everyone that, before you know it, it’ll be time to pull out parkas and trade noisy window air-conditioning