Alert archive / Illinois / Flash Flood Warnings in 2026
Flash Flood Warning 9, NWS Chicago, IL
NWS Chicago, IL issued this flash flood warning at Apr 15, 2026, 8:27 PM CDT for Boone County, Winnebago County, Illinois. It was in force for 4 hr. No storm report in the archive falls inside the area while it was in force.
The area
The counties it named.
The facts
- Issued
- Apr 15, 2026, 8:27 PM CDT (01:27 UTC)
- Expired
- Apr 16, 2026, 12:51 AM CDT
- In force
- 4 hr
- Issued by
- NWS Chicago, IL
- Area
- Storm-based polygon
- Flood severity
- None
Counties Boone County, IL, Winnebago County, IL
The radar
The Milwaukee radar (KMKX), 80 km from the middle of the area, began a volume at 01:31 UTC, the scan nearest the moment this went out.
Open the radar archive at this moment
The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.
The nearest sounding before it
Davenport, (KDVN), launched 00:00Z, 1.5 hours before the alert went out and 148 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.
- Mixed-layer CAPE
- 1272 J/kg
- Mixed-layer CIN
- -5 J/kg
- Mixed-layer LCL
- 1003 m above ground
- 0-6 km bulk shear
- 64 kt
- 0-1 km storm-relative helicity
- 167 m²/s²
- 0-3 km storm-relative helicity
- 209 m²/s²
- Significant tornado parameter
- 1.7
- Supercell composite
- 10.4
What forecasters said that day
The local office's own words before this flash flood warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Chicago, IL wrote its last area forecast discussion before this flash flood warning went out at Apr 15, 6:46 PM CDT, 1 hour 41 minutes earlier.
Area forecast discussion, Apr 15, 6:46 PM CDT, 1 hour 41 minutes before
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</html>Hazardous weather outlook, Apr 15, 3:21 PM CDT, 5 hours 6 minutes before
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Local storm report, Apr 15, 6:17 PM CDT, 2 hours 10 minutes before
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</html>Local storm report, Apr 15, 6:19 PM CDT, 2 hours 8 minutes before
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</html>Local storm report, Apr 15, 6:22 PM CDT, 2 hours 5 minutes before
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</html>The office that day
Everything else NWS Chicago, IL issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 15, 7:56 PM CDT | Tornado Warning | LOT | Ogle, Winnebago | 34 min |
| Apr 15, 8:19 PM CDT | Severe Thunderstorm Warning | LOT | Winnebago | 24 min |
| Apr 15, 9:20 PM CDT | Special Marine Warning | LOT | 115 min | |
| Apr 15, 9:38 PM CDT | Severe Thunderstorm Warning | LOT | DuPage, Kane, Kendall, Will | 55 min |
| Apr 15, 9:48 PM CDT | Special Marine Warning | LOT | 117 min | |
| Apr 15, 9:51 PM CDT | Severe Thunderstorm Warning | LOT | Cook, DuPage | 40 min |
| Apr 16, 3:03 AM CDT | Marine Dense Fog Advisory | LOT | 6 hr | |
| Apr 16, 3:29 AM CDT | River Flood Warning | LOT | Kane, Kendall | 13 days |
| Apr 16, 7:30 AM CDT | River Flood Warning | LOT | Boone, Winnebago | 3 days |
| Apr 16, 7:58 AM CDT | River Flood Warning | LOT | Winnebago | 14 days |
| Apr 16, 11:01 AM CDT | River Flood Warning | LOT | Winnebago | 13 days |
| Apr 16, 11:17 AM CDT | River Flood Warning | LOT | Ogle | 21 days |
| Apr 16, 11:24 AM CDT | River Flood Warning | LOT | Winnebago | 4 days |
| Apr 16, 11:29 AM CDT | River Flood Warning | LOT | Winnebago | 10 days |
| Apr 16, 3:03 PM CDT | Marine Dense Fog Advisory | LOT | 19 hr |
Nearby
Flash Flood Warnings in Illinois, 2026Every flash flood warning in 2026
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.