It was difficult enough to find a day warm enough to shed a sweater or jacket last summer—let alone run an air conditioner. Statewide, the season was the 5th coolest since 1895. But across Illinois—and Chicago in particular—the opening days of June 2005 couldn’t be more different. Hot weather has arrived—and early too! At Midway Airport, not only have this month’s first nine days averaged 8° above normal and 6° above last year, but together, they rank 6th warmest of all June 1-10 periods at the South Side site since 1928.
While rainfall here continues sub-par overall, drenching downpours erupted beneath 52,000 ft. high t-storms in the Plains Thursday along with a swarm of more than three dozen twisters. By late evening, 200 reports of severe weather had flooded into NOAA’s Storm Prediction Center. Rains exceeded 2.50” in an hour over parts of Missouri.
Midway airport’s 91° high on Wednesday, the 4th consecutive day of 90°+, tied the seasonal total of four 90° days for all of last year’s chilly summer. Midway’s 77-year normal tallies 24 days of 90°+. O’Hare topped out at 89°, cooled by an afternoon thunderstorm and nearly a quarter inch of rain. These widespread storms of recent days should increase in areal coverage Thursday, when a cold front attempts to break east from the chilly Rockies toward the Midwest, stalling west of Chicago.
However, remnants of the decaying boundary should push into the Chicago area for the best chance of needed rains Thursday and to a lesser extent on Friday.
Heat and humidity retain their grip on the region into next week, but models now present a convincing case for solid cold frontal passage Tuesday with temperature settling back to normal Wednesday.
The mercury touched 92° at O’Hare on Tuesday for the first official 90° reading in Chicago this year. Midway’s 93° was the third consecutive day of 90° or better, while the high for the state was Pontiac’s 97°. A lake breeze kept the lakefront a little cooler, with only 84° reported at Northerly Island. Consecutive model runs get hotter and hotter each day and now forecast no significant relief from the heat and humidity for the next seven days and beyond. If the forecast verifies, it would develop into an unprecedented heat wave so early in the season.
Amidst this heat and humidity is and unstable atmosphere. Thunderstorms in this environment have developed somewhere in the Chicago area the past four afternoons, and this aspect of the forecast should also remain through the period. The best moisture and instability gather Thursday and Friday, and hence best chance for needed rain then.