Multiple rounds of heavy rain fell between July 2 and July 4, leading to flash flooding in streets and rising river levels across the greater Chicago region, with some municipalities reporting 8 to 10 inches of rain over the 48-hour period.

According to the Metropolitan Water Reclamation District of Greater Chicago, its two largest Deep Tunnel reservoirs are nearly at capacity. 

The McCook reservoir, serving central Chicago and 36 municipalities, was approximately 98% full and holding 3.4 billion gallons of water as of Monday morning. The Thornton reservoir, serving the South Side of Chicago and 13 south suburban municipalities, was 94% full and holding 7.3 billion gallons.

If the Thornton reservoir reaches capacity, the MWRD warned that communities in the south suburbs could face an increased risk from overbank flooding.

The first of four rounds of storms struck the evening of July 2, followed by two rounds on July 3 that also saw damaging winds. Some of the heaviest rains fell on July 4, at a point when soils were already nearly completely saturated, leading to a “significant flash flood event across the western Chicago suburbs,” the National Weather Service said.

Official gauges at Chicago's airports recorded 3.53 inches and 3.05 inches at O'Hare and Midway, respectively. Further south in Cook County, Flossmoor recorded 6.37 inches. To the west, the Aurora airport notched 8.2 inches of rain.

Drier and cooler weather is expected through mid-week, with the chance for more rain returning on Thursday, according to the weather service.