Coolest temp here in 28 days—only a week after deadly heat

Few here would have thought Tuesday’s official 78° Chicago high temperature was possible so soon after last week’s deadly intense heat. There’s been only one daytime reading in the past 28 days—a 77° high back on July 21—which has been lower. The cooler air arrived within a Canadian high pressure responsible for producing nighttime temperatures in the low 40s in northwest Wisconsin.
Careful observers here no doubt note the first subtle signs that summer is maturing and that autumn draws closer. Wednesday hosts 67 fewer minutes of daylight after six weeks during which days have grown shorter. Days, once 913 minutes in length as summer commenced on June 21, have shrunk to 846 minutes and the sun treks across Chicago skies 8% lower in the sky. This reduces the solar energy August sunlight delivers by 11% compared to June, the month with the most energetic sunlight.
-Tom Skilling