Dec. 10, 2004 | Weather | WGNTV.com | WGN TV

Dec. 10, 2004

Dear Tom, When (and why) was the largest temperature difference between readings at O'Hare and Midway? Rick Burdsall, Palatine, Ill. Dear Rick, The magnitude of temperature variations that can occur across Chicagoland invariably surprises even our most weather-seasoned residents. During the 46 years (1959-2004) for which comparative temperature data are available for Midway and O'Hare, Jan. 18, 1987, stands as the day that produced the greatest temp variance between the two sites: 20°. Radiational cooling was the culprit. A snowstorm that put down five inches of snow ended by noon on Jan. 18, but an insulating overcast persisted. Temperatures under the clouds held in the 20s and Midway's low was 24°. At O'Hare, however, the sky cleared at night and radiational cooling sent temperatures crashing to a frigid 4°.