In the last 24 hours, Chicago's temperature has plunged from an asphalt-melting 35°C to a shiver-inducing 12°C:
(The chart shows degrees Celsius along the left and local time along the bottom.)
The drop right before 9am caught me by surprise. When I left the house (and it was 19°C outside), the polo and jeans I have on seemed appropriate. Three hours later, with Weather Bug reporting 10°C at the nearest station and O'Hare reporting 12°C, I really wish I'd brought a jacket to work.
WGN points out that the last three days comprise the hottest early-season heat wave since 1933.
Glad that's over...
Update, 12:39 CT: Weather Bug now reports 9°C at the Latin School, but O'Hare is holding steady at 12°C.