Clouds trapped beneath inversion to deny Chicago 70°

It’s not easy for the atmosphere to produce a 70° temperature this time of the year. Days are shorter, clouds more extensive (November is the city’s 2nd cloudiest month) and the sun traverses Chicago skies farther and farther south with each passing day, reducing the amount of energy that sunlight delivers. It’s no accident only 47 of the 11,097 temperatures above 70° at Midway Airport since observations began there in 1928 have occurred beyond Nov. 8. Complicating chances for such warmth Wednesday are fog and clouds trapped beneath a temperature inversion—an atmospheric set-up in which warm air aloft extinguishes the normal vertical mixing of air which might eradicate clouds. Though 10 states as close as Nebraska and South Dakota hosted near 80° highs Tuesday-readings 30° above normal-the lack of significant sunshine here Wednesday will inhibit the warm air’s eastward expansion. -Tom Skilling