The month’s 11th excursion above 70° Thursday—the most of any April since 1977—lasted just an hour before a back-door cold front swept the area. Such fronts derive the “back-door” label because their motion is opposite the norm—some would say “backwards.” Thursday’s front approached from the east rather than the west. By nightfall, the westbound front had cleared the Fox Valley and was continuing its westward trek.
The area’s precipitous return to chilly temperatures resulted from a vigorous post-frontal temperature plunge, which first commenced on Lake Michigan’s western shore around midday from Waukegan south to Chicago’s lakefront. By 2:05 p.m. Thursday, it had reached O’Hare. Readings there fell the remainder of the afternoon and evening, reaching 54° at 6 p.m. and 45° at 10 p.m. The 26-degree plunge over 10 hours rendered Thursday’s 71° high the city’s shortest spell of 70° warmth so far this month.
--Tom Skilling, WGN-TV Meteorologist
WGN-TV Chief Meteorologist Tom Skilling and the WGN Weather Center staff provide daily coverage of weather in the Chicago area.
