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Biggest day to next Sept temp drop here in 31 yrs giving way to warming, windy, wet fall storm coming

by Tom Skilling Today at 1AM

Happy Wednesday all!  Sunshine’s welcome return sets the stage for warming temperatures—and not a moment too soon. Chicagoans were forced to deal with a jarring 25-degree Monday to Tuesday high temperature plunge—the biggest to occur here in a September in 31 years.  Such a pullback is the equivalent of going from July weather in Chicago to Halloween level temps in just a day.

There have been 7 comparably sharp, day-to-next September temp pullbacks since observations began at O’Hare in 1959–the most recent back in 1983.  That chill swept into parts of the Chicago metro late Monday and has fanned out into other areas of the Midwest.  It turns out  Monday evening has been beaten only once before to 53-degrees Sept. 20-21, 2014.

The temporary warming underway in Wednesday’s southeast flow—a wind regime sure to at least modestly cool Chicago beaches holding air temperatures in the 60s there— is to accelerate Thursday as south winds associated with the developing fall storm over the Plains take hold and strengthen across the region. Just how high Thursday’s temps end up going then will depend a great deal on how much rain falls with a developing autumn storm predicted to sweep into the area.  Both the areal coverage and the intensity of the new storm system’s rainfall will have to be monitored, but early indications point to a  potentially significant rainfall event in which anywhere from 0.50″ (on the low side) and 2.57″ on the high side of computer rainfall projections on this system fall and other forecast tools which suggest big rains are entirely possible

A storm intensifies when the air ascending into it does so with increasing speed. This sets into motion a chain of atmospheric events which increase a storm’s winds while allowing a generous supply of moisture to floods into it.  Precipitation increases  when this happens—but so does the supply of colder air wrapping into the back side of the storm and eventually riding its counterclockwise into the Chicago area early Thursday.

Tom Skilling

Tom Skilling

Tom Skilling, WGN-TV chief meteorologist, appears weekdays on WGN Midday News, WGN Evening News and WGN News at Nine. He celebrated his 30th anniversary with WGN-TV in August 2008. Since 1997, Skilling has masterminded the weather page in the Chicago Tribune. In the city of Chicago and beyond, he has become the superman of meteorology: when in doubt, it is Tom that the city turns to when figuring out the mysteries of nature. WGN-TV received the 2005 Environmental Reporting Award from the Audubon Society, an accomplishment that is due to Tom's performance.

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