The situation right now
The National Weather Service in Chicago has issued a Flash Flood Warning for southern De Kalb County, northern La Salle County, and Lee County in north central Illinois, effective 2:12 AM CDT Sunday, September 20, and running until 8:00 AM CDT. Doppler radar shows thunderstorms producing heavy rain across the warned area — up to 3 inches have already fallen, with rainfall rates of 1.5 to 2.5 inches per hour and another 1 to 3 inches possible. Flash flooding is ongoing or expected to begin shortly. This is the exact interior-flooding profile restoration teams see most: fast water in homes, not rising rivers. This is a live snapshot as of early Sunday morning. Conditions change fast — always verify with the National Weather Service for your specific county or ZIP code.
De Kalb, La Salle & Lee Counties, IL — Flash Flood Warning
Issued by NWS Chicago at 2:12 AM CDT; expires 8:00 AM CDT. Hazard, verbatim from the alert: flash flooding caused by thunderstorms, radar-indicated. At 2:12 AM CDT, Doppler radar indicated thunderstorms producing heavy rain; up to 3 inches of rain have fallen, expected rainfall rates of 1.5 to 2.5 inches per hour, with additional amounts of 1 to 3 inches possible in the warned area.
Locations in the warning path, per NWS: Sandwich, Mendota, Amboy, Sheridan, Shabbona, Lake Holiday, Hinckley, Somonauk, Earlville, Waterman, Serena, Leland, Paw Paw, Sublette, Woodhaven Lakes, Millington, Lee, Compton, Troy Grove, Nelson, West Brooklyn, Harmon, Triumph, Prairie Center, and Lee Center.
Expected impacts, verbatim: rapid-onset flooding of creeks, streams, drainage ditches, streets, underpasses, low-lying areas, and other poor drainage areas. Persons along creeks, drainage ditches, and other waterways should take immediate precautions to protect life and property.
Sources: NWS Chicago, weather.gov.
Stay safe tonight
Turn around, don’t drown when encountering flooded roads — most flood deaths occur in vehicles. Never drive through flooded roadways; 6 inches of moving water can knock you down, 12 inches can carry away a car. It is harder to recognize the dangers of flooding at night — be especially cautious. If water enters your home: stay out of standing water where electricity may be present, avoid the basement until water recedes and power is confirmed off, and photograph everything before any cleanup — documentation matters for insurance. Then call a local restoration contractor; water left sitting starts a second wave of damage within a day.
What this means for restoration teams
Rates of 1.5 to 2.5 inches per hour on already-saturated ground mean rapid-onset interior flooding: water intrusion through doors and window wells, saturated drywall and insulation, and sewage backup in low-lying pockets of the warned area. With flash flooding ongoing at 2 AM, first water-intrusion calls typically start within hours of water receding and keep coming for days as people discover damage. Mold risk begins within 24 to 48 hours — the drying play starts now.
The play: stage equipment now — air movers, dehumidifiers, extraction units — and pre-position drying assets across the De Kalb / La Salle / Lee triangle before first light. Keep an on-call rotation through the morning; Sunday-morning water events generate calls all day as residents wake to standing water. Capture address, water source, and affected areas on the very first call. Field discipline: photo-document before mitigation, moisture-map every affected room, and keep the homeowner’s payment responsibility clear in writing before work starts.
FEMA & federal assistance
If the flooding damages your home, the FEMA Helpline is 1-800-621-3362 (7 a.m.–10 p.m. local time, 7 days a week). You can also apply at DisasterAssistance.gov, through the FEMA mobile app, or find a recovery center at fema.gov/drc. Basic eligibility generally requires citizenship or qualified status, identity verification, proof of occupancy or ownership, and unmet needs not covered by insurance. Apply as soon as it is safe to do so.
Looking ahead
This warning runs until 8:00 AM CDT. Overnight, watch for additional rounds of thunderstorms training over the same counties, and creeks and drainage ditches that crest later even after rain stops. The NWS will update or extend the warning if conditions warrant; check the NWS Chicago page for the latest. For restoration operators, the demand window is Sunday: calls start as water recedes and run for days as damage is discovered.
Sources & how to verify
NWS Chicago alert (issued 2:12 AM CDT Sept 20, 2026): weather.gov — NWS Chicago office: weather.gov/lot/. To verify for your county or ZIP, go to weather.gov and enter your ZIP, or check your local NWS office page.
This post is for informational purposes and is not an official weather warning. Always follow instructions from local authorities and the National Weather Service.
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