Flat Rock, IL Hail Storm – September 2026

Flat Rock, IL on September 18, 2026 saw late-afternoon hail that reached 1.77 inches. The multi-zone thunderstorm produced radar-detected hail swaths and two National Weather Service alerts during the event.

What Happened

The storm moved through the Flat Rock area in the late afternoon of September 18, 2026 and has since concluded. The NWS issued two alerts covering the event. At 3:31 PM CDT (20:31 UTC) officials issued a warning noting 1.00-inch hail with an NWS warning only designation. At 4:09 PM CDT (21:09 UTC) dual-polarization radar detected 1.17-inch hail across the warning area. Radar and subsequent field information indicate a peak hail size of 1.77 inches along parts of the swath.

Radar-detected hail signatures tracked across multiple zones within the warning area. The alert sequence shows initial warning coverage followed by radar confirmation of elevated hail diameters as the storm intensified in late afternoon.

Damage Assessment

Hail between 1.00 and 1.77 inches can produce vehicle body dents and surface damage to metal trim. Expect door and hood dimpling on unprotected cars parked in the open. This size range commonly removes shingle granules and causes bruising to asphalt shingles, reducing expected roof life and accelerating wear where impacts concentrated.

At 1.50 inches and larger, impacts can dent soffits, gutters, and air-conditioning condenser fins. Windows and skylights are at increased risk when hail reaches or exceeds 1.75 inches. Exterior vinyl siding and fiber-cement panels may show cosmetic cracking or pitting where strikes were frequent.

What Contractors Should Know

Prioritize safety and documentation on initial visits. Perform exterior inspections from the ground and from a stable ladder; avoid unsafe roof walks until a full safety assessment is complete. Photograph hail impacts with scale references and multiple angles. Note timestamps and GPS coordinates when possible. Inspect roof edges, valleys, and south-facing slopes first. Check HVAC condensers, vehicle surfaces if on-site, gutters, and exposed trim for impact patterns that indicate strike concentration.

Measure and record hail diameter where remaining fragments or indent impressions are found. Evaluate shingles for granule loss and bruise patterns that indicate filed replacement rather than spot repairs. Provide clients with a clear scope and photographic evidence for claims. Where roof openings or exposed interiors exist, recommend temporary tarping and coordinate with insurers before permanent repairs.

See the Strike Map for the radar-confirmed hail swath for this event.