Wednesday evening, June 28, saw strong to severe storms redevelop and track across far northern Illinois. Some of the initial storms were supercells, bringing low-level rotation and a tornado threat to parts of Winnebago and Boone Counties. There were also areas of straight-line wind damage, including into Lake County Illinois.
The main story though was the significant flash flooding in Winnebago and Boone Counties due to 3 to 6+ inches of rain, mainly in less than four hours. The flash flooding was extreme enough to cause dozens of roads to be flooded and impassable across the two counties, include parts of the cities of Rockford and Belvidere. There were reports from Emergency Management of numerous vehicles stranded and drivers having to be rescued, as well as creeks over their banks including Kent Creek in Rockford.
Prior to the event, the NWS had been noting potential for heavy rain in Weather Story graphics for a few days in advance, and had issued a Flash Flood watch early Wednesday evening. This was shortly followed by a Flash Flood Warning at 8:24 p.m., updated to a Flash Flood Emergency at 9:32 p.m. given the flooding magnitude
PRELIMINARY LOCAL STORM REPORT...SUMMARY NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL 204 AM CDT THU JUN 29 2017 ..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... ..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... ..REMARKS.. 0740 PM TSTM WND DMG DURAND 42.44N 89.33W 06/28/2017 WINNEBAGO IL PUBLIC 5 TREES AND NUMEROUS TREE BRANCHES REPORTED DOWN. 3 INCHES OF RAINFALL REPORTED IN 2 HOURS. REPORT FROM SOCIAL MEDIA. 0759 PM TSTM WND DMG MACHESNEY PARK 42.36N 89.04W 06/28/2017 WINNEBAGO IL PUBLIC NUMEROUS TREE BRANCHES DOWN AND 1 FT DIAMETER TREE UPROOTED. CEMENTED FLAG POLE ALSO BENT FROM WIND GUST 0800 PM TSTM WND GST WINNEBAGO 42.27N 89.24W 06/28/2017 E60.00 MPH WINNEBAGO IL PUBLIC TORRENTIAL RAINFALL AND WIND, ESTIMATED GUST GREATER THAN 60 MPH 0806 PM TSTM WND DMG MACHESNEY PARK 42.36N 89.04W 06/28/2017 WINNEBAGO IL BROADCAST MEDIA PART OF HOUSE ROOF BLOWN OFF. 0810 PM TSTM WND DMG ROCKFORD 42.27N 89.06W 06/28/2017 WINNEBAGO IL TRAINED SPOTTER 8 DIAMETER TREE LIMBS, POWER LINES ON 11TH STREET NEAR SANDY HOLLOW 0822 PM TSTM WND DMG BELVIDERE 42.25N 88.85W 06/28/2017 BOONE IL EMERGENCY MNGR NEAR TOWN HALL ROAD, POWER POLES DOWN 0825 PM FLASH FLOOD BELVIDERE 42.25N 88.85W 06/28/2017 BOONE IL EMERGENCY MNGR EAST ROAD BETWEEN 4TH AND 8TH IS CLOSED DUE TO FLASH FLOODING 0835 PM FUNNEL CLOUD MARENGO 42.25N 88.60W 06/28/2017 MCHENRY IL LAW ENFORCEMENT OBSERVED BY MARENGO POLICE. 0845 PM TSTM WND DMG ANTIOCH 42.47N 88.08W 06/28/2017 LAKE IL EMERGENCY MNGR TREES DOWN ON ILLINOIS ROUTE 173 0910 PM TSTM WND GST 5 SSE BEACH PARK 42.36N 87.81W 06/28/2017 M52.00 MPH LMZ740 IL C-MAN STATION 45 KT. 0930 PM FLASH FLOOD ROCKFORD 42.27N 89.06W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR REPORTS OF NUMEROUS CARS STRANDED ON FLOODED ROADWAYS ESPECIALLY NEAR ROCKFORD VIADUCTS. KENT CREEK IS ALSO OUT OF ITS BANKS. 0930 PM FLOOD GURNEE 42.38N 87.94W 06/28/2017 LAKE IL TRAINED SPOTTER 1.05 INCHES OF RAIN HAD FALLEN BY 930 1000 PM HEAVY RAIN LOVES PARK 42.34N 89.01W 06/28/2017 M5.69 INCH WINNEBAGO IL PUBLIC REPORT FROM SOCIAL MEDIA. 1000 PM FLASH FLOOD ROCKFORD 42.27N 89.06W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR PEAK OF WATER RESCUES FROM STALLED VEHICLES DUE TO FLASH FLOODING IN THE CITY. NUMEROUS ROADS IMPASSABLE DUE TO WATER. 1000 PM HEAVY RAIN WINNEBAGO 42.27N 89.24W 06/28/2017 M5.21 INCH WINNEBAGO IL PUBLIC REPORT FROM SOCIAL MEDIA. 1000 PM HEAVY RAIN ROCKFORD 42.27N 89.06W 06/28/2017 M2.37 INCH WINNEBAGO IL OFFICIAL NWS OBS 2 HOUR AMOUNT AND STILL RAINING. 1000 PM FLASH FLOOD PECATONICA 42.31N 89.36W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR NUMEROUS RESIDENTIAL ROADS IMPASSABLE DUE TO WATER. 1000 PM FLASH FLOOD MACHESNEY PARK 42.36N 89.04W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR NUMEROUS RESIDENTIAL ROADS IMPASSABLE DUE TO WATER. 1000 PM FLASH FLOOD LOVES PARK 42.34N 89.01W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR NUMEROUS RESIDENTIAL ROADS IMPASSABLE DUE TO WATER. 1000 PM FLASH FLOOD 4 ESE ROCKFORD 42.25N 88.99W 06/28/2017 WINNEBAGO IL EMERGENCY MNGR WATER ACROSS A PARKING LOT AT A PHARMACY. CARS STRANDED AND PEOPLE TEMPORARILY UNABLE TO LEAVE THE BUILDING. 1000 PM HEAVY RAIN ROCKFORD 42.27N 89.06W 06/28/2017 M5.48 INCH WINNEBAGO IL PUBLIC 5.48 INCHES MEASURED AT ROCKFORD INTERNATIONAL GOLF COURSE. 3.48 INCHES MEASURED IN DOWNTOWN ROCKFORD. REPORT FROM SOCIAL MEDIA. 1008 PM HEAVY RAIN PECATONICA 42.31N 89.36W 06/28/2017 M5.00 INCH WINNEBAGO IL TRAINED SPOTTER STORM TOTAL SO FAR. DITCHES ON FULL. 1030 PM FLASH FLOOD MARENGO 42.25N 88.60W 06/28/2017 MCHENRY IL LAW ENFORCEMENT WATER OVER PART OF ILLINOIS ROUTE 23. 1035 PM HEAVY RAIN ROCKFORD 42.27N 89.06W 06/28/2017 M4.25 INCH WINNEBAGO IL TRAINED SPOTTER 0.45 ICHES OF RAIN FELL THIS MORNING WITH AN ADDITIONAL 3.80 INCHES THIS EVENING 1100 PM FLASH FLOOD BELVIDERE 42.25N 88.85W 06/28/2017 BOONE IL LAW ENFORCEMENT SIGNIFICANT FLOODING ON MANY ROADWAYS IN BELIVDERE WHERE THERE WERE WATER RESCUES FROM STRANDED VEHICLES. NUMEROUS ROADS CLOSED DUE TO FLOODING THROUGHOUT THE COUNTY. 1100 PM FLASH FLOOD ALGONQUIN 42.16N 88.30W 06/28/2017 MCHENRY IL LAW ENFORCEMENT ALGONQUIN ROAD IMPASSABLE DUE TO WATER. 1140 PM TSTM WND DMG GLENDALE HEIGHTS 41.92N 88.08W 06/28/2017 DUPAGE IL PUBLIC SEVERAL POWERLINES DOWN AND A FEW SMALL TREES DOWN. SUSPECTED MICROBURST. TIME ESTIMATED FROM RADAR. 1200 AM HEAVY RAIN ROCKFORD AIRPORT 42.20N 89.10W 06/29/2017 M4.11 INCH WINNEBAGO IL OFFICIAL NWS OBS DAILY TOTAL MOST OF WHICH FELL IN THE EVENING. 1200 AM HEAVY RAIN 3 ENE ROSCOE 42.43N 88.95W 06/29/2017 M2.67 INCH WINNEBAGO IL TRAINED SPOTTER 1255 AM NON-TSTM WND GST PONTIAC 40.88N 88.64W 06/29/2017 M61.00 MPH LIVINGSTON IL AWOS DUE TO A WAKE LOW. 0130 AM FLASH FLOOD 4 SE BELVIDERE 42.21N 88.79W 06/29/2017 BOONE IL BROADCAST MEDIA DITCHES OVERFLOWED AND WATER ONTO GENOA ROAD.