On July 27, 2026, a powerful multi-cell thunderstorm complex swept across the Great Lakes region, producing 95 confirmed severe weather reports across Illinois, Indiana, Michigan, and Ohio. The system generated baseball-sized hail in Will County, peak wind gusts of 74 mph at Chicago Midway Airport, two confirmed tornadoes in DuPage and Vermilion Counties, and a trail of structural damage that extended from the Chicago suburbs all the way to the Dayton, Ohio metro area. THOR Storm Intelligence captured every report in real time from NOAA/SPC data feeds.
Executive Summary
This was a textbook progressive derecho-like event that organized across Wisconsin in the early afternoon and intensified as it moved southeast into the Chicago metro. The storm's peak intensity window — roughly 4:00 PM to 7:00 PM CDT — produced the most significant hail and wind reports across northern Illinois. A secondary wave then pushed east-southeast into Indiana and Ohio through the evening hours, generating widespread tree and structure damage from the Michiana corridor down through central Indiana and into the Dayton metro.
| State | Hail Reports | Wind Reports | Tornadoes | Peak Hail | Peak Wind |
|---|---|---|---|---|---|
| Illinois | 23 | 26 | 2 | 3.00" (baseball) — Shorewood | 74 mph — Midway Airport |
| Indiana | 0 | 29 | 0 | — | 60 mph — Rochester, Marion, Grissom AFB |
| Michigan | 2 | 3 | 0 | 1.50" — Oscoda area | Damaging (est.) |
| Ohio | 0 | 10 | 0 | — | Damaging — Dayton metro |
Timeline of Events
12:06 PM CDT — First reports, Upper Michigan. The day's first confirmed hail report came from Ontonagon County, Michigan, where a DNR ranger reported quarter-sized hail (1.00") near Lake of the Clouds. Time was estimated by radar. This was an isolated precursor cell well ahead of the main complex.
3:56 PM CDT — Northern Illinois ignites. The first Illinois hail report arrived from West Dundee in Kane County — quarter-sized hail (1.00"). Within 20 minutes, the storm was producing significantly larger stones. By 4:04 PM, Carol Stream in DuPage County was logging 1.75" hail. At 4:55 PM, a trained spotter in Clarendon Hills reported 2.00" diameter hail — hen-egg size — with the report relayed via NWS Chicago (LOT).
4:55–5:30 PM CDT — DuPage and Cook County peak intensity. This was the most active hail window for the Chicago metro. Westmont logged 2.50" hail at 5:18 PM. Willowbrook reported golf ball-sized hail (1.75") at 5:20 PM. Wind reports began stacking simultaneously: 72 mph at Oakbrook Terrace at 5:04 PM, 74 mph at Midway Airport at 5:40 PM (confirmed ASOS), and a peak gust of 74 mph recorded 3 miles offshore at the Harrison-Dever Crib weather buoy at 5:58 PM CDT. O'Hare Airport (ORD) logged a 62 mph gust at 9:37 PM as a second wave moved through.
4:55 PM CDT — Tornado confirmed, Glen Ellyn. NWS Chicago issued a tornado report for 1 NNW Glen Ellyn in DuPage County at 4:55 PM CDT. A photo passed along by spotters showed a tornado near the location of a radar-indicated Tornadic Debris Signature (TDS). Survey was ongoing as of the initial report. This is the same storm cell that produced the 2.00" hail in Clarendon Hills minutes earlier.
6:00–8:00 PM CDT — Storm pushes into Indiana. As the primary Illinois cells weakened, a reorganized line pushed into northwest Indiana. La Porte County reported a large tree down onto a car in La Porte city at 6:55 PM. By 7:10 PM, Walkerton in St. Joseph County had trees down on SR 104. The line continued southeast: Rochester in Fulton County logged a trained spotter report of 60 mph gusts at 7:30 PM, with multiple tree limbs 3–6 inches in diameter downed. Argos in Marshall County had siding ripped off a house at 7:35 PM. Utility poles were snapped in Valparaiso (Porter County) at 9:59 PM.
8:00–10:00 PM CDT — Central Indiana damage corridor. The storm complex continued tracking southeast through central Indiana. Alexandria in Madison County reported trees, power poles, and power lines downed across the northern part of the county at 9:10 PM. Marion in Grant County logged 60 mph gusts at 8:40 PM with trees downed on the south side of the city. Hartford City in Blackford County reported a very large tree down onto a home at 9:05 PM. Grissom Air Reserve Base (AWOS station KGUS) confirmed 60 mph gusts at 8:14 PM.
10:00 PM CDT — Ohio impact, Dayton metro. The system's eastern flank reached southwest Ohio late in the evening. New Paris in Preble County (west of Dayton) reported several trees downed at 10:07 PM. Arcanum in Darke County had trees down at 10:08 PM. The damage corridor tracked through Montgomery County (Brookville, Northridge), Warren County (Lebanon), and into Hamilton County (Silverton, Finneytown) — all reporting trees on structures and wires down between 10:24 PM and 11:35 PM CDT.
11:14 PM CDT — Second Illinois tornado, Hoopeston. Storm spotters captured video evidence of a tornado that briefly touched down 1 mile west of IL-1 near Hoopeston in Vermilion County. A power pole and street sign were damaged. This was a separate, later-developing cell well to the south of the primary complex, reported by NWS Lincoln (ILX).
Hail Impact Analysis — Priority Zones for Roofing Crews
The hail footprint was concentrated almost entirely in northern Illinois, with the Will County / Cook County corridor representing the highest-priority deployment zone. The Shorewood report of 3.00" (baseball-sized) hail at 8:41 PM CDT is the single most significant roof damage indicator from this event. Baseball-sized hail at terminal velocity produces kinetic energy sufficient to crack asphalt shingles, dent metal flashing, and fracture tile — even on newer roofs. The Westmont (2.50") and Clarendon Hills (2.00") reports from earlier in the afternoon indicate a broad hail swath across DuPage and Will Counties.
| Priority | Location | County | Hail Size | Time (CDT) | Notes |
|---|---|---|---|---|---|
| 1 | Shorewood / Four Seasons Park | Will, IL | 3.00" | 8:41 PM | Photo confirmed; hail collected and frozen |
| 2 | Westmont | DuPage, IL | 2.50" | 5:18 PM | NWS LOT confirmed |
| 3 | Clarendon Hills | DuPage, IL | 2.00" | 4:56 PM | Trained spotter; time estimated by radar |
| 4 | Willowbrook / Tinley Park | Cook, IL | 1.75" | 5:20–5:30 PM | Golf ball; amateur radio relay |
| 5 | Minooka / Shorewood (early) | Grundy/Kendall, IL | 1.50" | 8:38–8:46 PM | Ping pong ball; public reports |
| 6 | Watseka | Iroquois, IL | 1.75" | 10:35 PM | Multiple reports; golf ball size |
The Shorewood / Minooka / Grundy County corridor is particularly notable because it received two separate hail events — one in the late afternoon and a second, larger event in the evening — meaning cumulative roof exposure was higher than any single report suggests. Contractors working this area should expect to find damage on both the primary storm-facing slopes and secondary exposures.
Wind Damage Assessment
Wind damage was the dominant hazard for Indiana and Ohio. The 74 mph gusts recorded at Chicago Midway Airport represent near-damaging thunderstorm wind territory — sufficient to snap branches, damage soffits and fascia, and in some cases lift poorly-secured roofing materials. The offshore buoy reading of 74 mph at the Harrison-Dever Crib confirms the gust was not a localized station anomaly.
In Indiana, the damage was more diffuse but covered a large geographic area. Utility poles were snapped in Valparaiso (Porter County). A gas station canopy partially collapsed in Frankfort (Will County, IL). A large tree fell onto a home in Hartford City, Indiana. Power poles and lines were downed across Madison County. The pattern is consistent with a bowing line segment producing 55–65 mph winds across a 150-mile-long corridor from Lake County, Indiana to Delaware County (Muncie area).
In Ohio, the damage was primarily tree-related — large limbs and full trees downed across the Dayton northern suburbs. No structural collapses were reported, but the pattern of trees-on-structures in Northridge and Silverton suggests wind speeds in the 50–60 mph range at the leading edge of the system.
Tornado Activity
Two tornadoes were confirmed from this event, both in Illinois. The Glen Ellyn tornado (DuPage County, 4:55 PM CDT) occurred near a radar-indicated Tornadic Debris Signature, which is a strong indicator of ground contact. Survey work was ongoing as of the initial report. The Hoopeston tornado (Vermilion County, 11:14 PM CDT) was captured on video by storm spotters and caused minor infrastructure damage — a snapped power pole and street sign. Both are rated EF-unknown pending ground surveys.
THOR Storm Intelligence — How This Data Was Captured
Every event in this report was sourced from NOAA/SPC storm reports and ingested by THOR Storm Mapper within minutes of publication. The platform's regional impact view displayed county-level severity boundaries for DuPage, Cook, Will, and Grundy Counties while the storm was still active. The hail swath overlay — generated from SPC report coordinates — showed the geographic footprint of the hail corridor in real time, allowing contractors to identify which neighborhoods fell inside the damage zone before the storm had even cleared the area.
The AI Storm Intelligence Report feature used in generating this analysis is available to all THOR subscribers. It parses raw SPC event data — including NWS spotter comments, measured magnitudes, and confirmed locations — and produces a structured field intelligence report in under 60 seconds. Reports can be downloaded as Markdown for use in client proposals, insurance documentation, or internal crew briefings.
Data source: NOAA/SPC Storm Reports for July 27, 2026. All times converted to CDT (UTC-5). Report generated via THOR Storm Intelligence using verified SPC spotter reports. © 2026 THOR Storm Mapper. All rights reserved.