For the 30th time in 2005, temperatures at Midway Airport exceeded 90° Tuesday. The day’s high of 95° at both Midway and O’Hare—just 2 degrees shy of the 1913 record of 97°—tied as the city’s fourth warmest temperature to date. The warmest here has been 102° on July 24. An Aug. 9 hasn’t been warmer in 61 years—since a 97° high in 1944.
Tuesday’s heat pushes the average temperature at Midway Airport since June 1 to 77.4°, a reading 4.4 degrees above normal and advances the Meteorological Summer 2005 season to a ranking of 2nd warmest since 1928. Though heat relief is on the way, history strongly suggests Chicagoans haven’t seen the last of 90° temperatures. In previous comparably dry summers, an average of seven additional 90s have occurred beyond Aug. 10.
Every reporting station in the metro area reached or exceeded 90° Tuesday. Interestingly, the hottest area readings were at Rockford and Kenosha—both 97°.

Not since 1983 have the opening eight days of August failed to produce measurable rain at either of the city’s official weather observation sites. And while there are growing signs rain may appear on the scene over the coming week, Chicago’s rain deficit has grown to 10.12” since March 1. The dry weather’s impact has been devastating on the region’s corn crop. While some pockets of timely rainfall put some fields in better shape than others across northern and central Illinois, the latest USDA crop condition report rates 61% of Illinois’ corn crop in “poor” or “very poor” condition—the worst of any state in the Midwest.
Limited soil moisture contributed to low humidities amid Monday’s soaring Chicago readings. The area’s average daytime relative humidity of 54% was lower than the 69% average in perennially dry Phoenix, Ariz. The mercury climbed past 90° for the 29th time in 2005 at Midway (93°) and the 20th time at O’Hare (93°) Monday.

Yesterday, Midway hit 90° for the fifth time this month, and it looks like three more 90° days will be added to that total by midweek. Humidity will also slowly be on the rise. Showers and thunderstorms appear in the forecast each day starting Wednesday through next weekend. While the core of the jet stream still resides far to the north across southern and central Canada, light westerly winds aloft at this latitude allow low-level southerly flow to feed warm, moist air into northern Illinois. A cool front will sag south through Wisconsin, drifting through Chicago on the heels of a thunderstorm-producing low pressure center Friday. From that point on, the front will become quasi-stationary, with the potential to fluctuate north or south of the metro area. Current computer model projections have the front situated just south of Interstate 80 next weekend, but a slight repositioning to the north could radically change temperature and rainfall forecasts.