Multiple rounds of heavy rain producing storms moved across the region during the day and evening of June 15th, with an especially intense area of extreme rainfall rates during the mid-afternoon through early evening centered on the I-88 and I-290 corridors from the IL/IA state line through Chicago.
This rain resulted in widespread flash flooding, including the closure of a portion of I-290 (Eisenhower Expressway). In addition, the heavy rainfall and widespread storm coverage resulted in the cancellation or delays of hundreds of commerical flights in and out of Chicago.
While the environment was not conducive for long-lived or powerful tornadoes, a brief tornado threat existed with a few rotating storms known as supercells. This included with two storms in central Cook County, primarily west of downtown Chicago. Each of these had funnel cloud reports. There was also a brief tornado reported near the Will/Kanakakee County border, not far from I-57. It is still being verified if a tornado actually occurred, although it likely did based on reports and photos. We will be working with Will County Emergency Management today. A tornado warning was in effect for this storm.
The highest rainfall amounts reported were two and a half to five inches in parts of Cook, DuPage, Kane, and Will Counties, which include a large majority of Chicago and the metropolitan area.
The 2.56 inches observed at Chicago O'Hare International Airport on June 15th was a record for the calendar day, surpassing the old one of 0.96 inches in 1982. This was the highest daily rainfall amount since August 4, 2014 (2.76 inches). The five day total of rain from June 11th-15th is 3.96 inches and is the highest since April 15-19, 2013 (5.93 inches).
The 3.09 inches measured at Chicago DuPage Airport on Monday, June 15th, and the 2.86 inches at Aurora Airport in Sugar Grove, were the highest calendar day precipitation totals in their nearly complete data-set since September 13, 2008
The threat of an active pattern with heavy rain and flooding had been mentioned in NWS outlooks as early as Tuesday, June 9th. A Flash Flood Watch was issued at 4 a.m. Monday morning, and Flash Flood Warnings were issued at 4:24 pm (I-88 corridor), 6:09 pm (I-80 corridor).