Flash Flood Warning Issued for Boone, Lake, and McHenry Counties in Illinois
This alert is no longer in effect.
NOAA issued it on April 25, 2026, 4 months ago. Warnings of this kind stay in effect for hours to a few days, so this page is a historical record of what was issued, not a current warning. For conditions where you are right now, check weather.gov (US), weather.gc.ca (Canada), the Met Office (UK), or the Bureau of Meteorology (Australia).
Areazine synthesizes this NWS weather alert directly from NOAA's official public data feed. See our methodology for full source attribution and refresh cadence.
The National Weather Service has issued a Flash Flood Warning for Boone, Lake, and McHenry counties in Illinois until 2:00 AM CDT on April 18, 2026, due to heavy rain causing rapid-onset flooding.
Read this weather record in 30 seconds
- Record type
- Flash Flood Warning
- Affected area
- Northern Illinois
- Issued
- April 25, 2026
- Issuing authority
- NWS Chicago IL
Flood notices turn on location and timing. Treat the named area as this record's scope; do not assume nearby counties, parishes, or waterways were included.
Record status: historical. It was issued 4 months ago; use the issuing agency's live warning service for current conditions in Northern Illinois.
Flash Flood Warning in Northern Illinois
Alert Details
A Flash Flood Warning has been issued by the National Weather Service (NWS) Chicago IL. It is effective from April 17, 2026, at 8:12 PM CDT until April 18, 2026, at 2:00 AM CDT.
Affected Areas
The warning affects Boone County, Lake County, and McHenry County in Illinois. Specific locations that may experience flash flooding include Waukegan, Arlington Heights, Palatine, Buffalo Grove, Crystal Lake, Wheeling, Northbrook, North Chicago, Gurnee, Mundelein, Algonquin, Highland Park, Lake in the Hills, Round Lake Beach, McHenry, Belvidere, Vernon Hills, Woodstock, Zion, and Huntley.
What You Should Do
Persons along creeks, drainage ditches, and other waterways should take immediate precautions to protect life and property. Avoid areas prone to flooding as rapid-onset flooding is imminent or may already be occurring.
Expected Conditions
Thunderstorms are producing extremely heavy rain with rainfall rates up to an inch in less than 30 minutes. Additional rainfall amounts of 1 to locally over 2 inches are expected, leading to flash flooding in creeks, streams, drainage ditches, streets, underpasses, low-lying areas, and other poor drainage areas.
Timeline
The alert is effective from April 17, 2026, at 8:12 PM CDT and ends on April 18, 2026, at 2:00 AM CDT.
Original source: NOAA Official Notice ↗
Related Weather Alerts
All Weather Alerts →Nationwide notices with similar length or severity timing 8
Two Areazine-derived peer sets for this NWS weather alert: nearest notices by body length and by same severity near the same agency date. Peers come from other categories so they are not the same-feed Related list above.
Similar body length
Nearest notices by article body length (1,345 characters here).
Similar severity timing
Same severity (high) notices issued closest in time to April 25, 2026.
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