Alert archive / Illinois / Flash Flood Warnings in 2024
Flash Flood Warning 21, NWS Chicago, IL
NWS Chicago, IL issued this flash flood warning at Jul 23, 2024, 5:38 PM CDT for Boone County, McHenry County, Illinois. It was in force for 3 hr. 2 reports came from inside the area while it was in force.
The area
The outline as issued, with what was reported inside it.
The facts
- Issued
- Jul 23, 2024, 5:38 PM CDT (22:38 UTC)
- Expired
- Jul 23, 2024, 8:45 PM CDT
- In force
- 3 hr
- Issued by
- NWS Chicago, IL
- Area
- Storm-based polygon
- Flood severity
- None
Counties Boone County, IL, McHenry County, IL
The radar
The Milwaukee radar (KMKX), 78 km from the middle of the area, began a volume at 22:40 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.
What was reported inside it
| Time | Report | Where | Remark |
|---|---|---|---|
| Jul 23, 6:00 PM CDT | FLOOD | 3 Nw Garden Prairie, IL | Several roads and fields flooded northeast of Belvidere and north of Garden Prairie. Some roads had several inches of standing water on them and had to be closed. |
| Jul 23, 6:30 PM CDT | RAIN 4.21 | 3 Ne Garden Prairie, IL | Measured rainfall of 4.21 inches in 2 hours at a personal weather station. |
Local storm reports filed while the alert was in force, from inside its polygon or its counties.
The nearest sounding before it
Davenport, (KDVN), launched 12:00Z, 10.6 hours before the alert went out and 165 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
- 451 J/kg
- Mixed-layer CIN
- -58 J/kg
- Mixed-layer LCL
- 979 m above ground
- 0-6 km bulk shear
- 12 kt
- 0-1 km storm-relative helicity
- -8 m²/s²
- 0-3 km storm-relative helicity
- 18 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
013
WGUS53 KLOT 232238
FFWLOT
ILC007-111-240145-
/O.NEW.KLOT.FF.W.0021.240723T2238Z-240724T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Chicago IL
538 PM CDT Tue Jul 23 2024
The National Weather Service in Chicago has issued a
* Flash Flood Warning for...
East Central Boone County in north central Illinois...
West Central McHenry County in northeastern Illinois...
* Until 845 PM CDT.
* At 538 PM CDT, Doppler radar indicated thunderstorms producing
heavy rain across the warned area. Between 2 and 3 inches of rain
have fallen. Additional rainfall amounts of 1 to 2 inches are
possible in the warned area. Flash flooding is ongoing or expected
to begin shortly.
HAZARD...Flash flooding.
SOURCE...Radar.
IMPACT...Rapid-onset flooding of creeks, streams, drainage
ditches, streets, underpasses, low-lying areas, and
other poor drainage areas.
* Some locations that will experience flash flooding include...
Marengo.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
A Flash Flood Warning means rapid-onset flooding is imminent or may
already be occurring. Persons along creeks, drainage ditches, and
other waterways should take immediate precautions to protect life
and property.
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 4227 8878 4228 8880 4231 8877 4230 8869
4230 8863 4226 8860 4225 8860 4225 8866
4226 8874
FLASH FLOOD...RADAR INDICATED
$$
DK1 follow-up statement
237
WGUS73 KLOT 240140
FFSLOT
Flash Flood Statement
National Weather Service Chicago IL
840 PM CDT Tue Jul 23 2024
ILC007-111-240150-
/O.EXP.KLOT.FF.W.0021.000000T0000Z-240724T0145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Boone IL-McHenry IL-
840 PM CDT Tue Jul 23 2024
...FLASH FLOOD WARNING WILL EXPIRE AT 845 PM CDT THIS EVENING FOR
EAST CENTRAL BOONE AND WEST CENTRAL MCHENRY COUNTIES...
The heavy rain has ended. Flooding is no longer expected to pose a
threat. Please continue to heed remaining road closures.
&&
LAT...LON 4227 8878 4228 8880 4231 8877 4230 8869
4230 8863 4226 8860 4225 8860 4225 8866
4226 8874
$$
DKThe office that day
Everything else NWS Chicago, IL issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 23, 4:35 PM CDT | Special Weather Statement | LOT | McHenry | 55 min |
| Jul 23, 5:07 PM CDT | Areal Flood Advisory | LOT | Boone, McHenry | 3 hr |
| Jul 23, 6:36 PM CDT | Special Weather Statement | LOT | LaSalle | 39 min |
Nearby
Flash Flood Warnings in Illinois, 2024Every flash flood warning in 2024
Sources
The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.