Alert archive / Illinois / Flash Flood Warnings in 2026
Flash Flood Warning 20, NWS St. Louis, MO
NWS St. Louis, MO issued this flash flood warning at May 18, 2026, 5:06 PM CDT for Jefferson County, Saint Louis County, City of Saint Louis, Missouri; 4 counties in 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 outline as issued.
The facts
- Issued
- May 18, 2026, 5:06 PM CDT (22:06 UTC)
- Expired
- May 18, 2026, 8:57 PM CDT
- In force
- 4 hr
- Issued by
- NWS St. Louis, MO
- Area
- Storm-based polygon
- Flood severity
- None
Counties Clinton County, IL, Madison County, IL, Monroe County, IL, Saint Clair County, IL, City of Saint Louis, MO, Jefferson County, MO, Saint Louis County, MO
The radar
The St Louis radar (KLSX), 54 km from the middle of the area, began a volume at 22:08 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
Lincoln, IL (KILX), launched 12:00Z, 10.1 hours before the alert went out and 222 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
- 850 J/kg
- Mixed-layer CIN
- -80 J/kg
- Mixed-layer LCL
- 966 m above ground
- 0-6 km bulk shear
- 25 kt
- 0-1 km storm-relative helicity
- 301 m²/s²
- 0-3 km storm-relative helicity
- 331 m²/s²
- Significant tornado parameter
- 0.8
- Supercell composite
- 8.8
The text
As transmitted.
728
WGUS53 KLSX 182206
FFWLSX
ILC027-119-133-163-MOC099-189-510-190200-
/O.NEW.KLSX.FF.W.0020.260518T2206Z-260519T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service St Louis MO
506 PM CDT Mon May 18 2026
The National Weather Service in St Louis has issued a
* Flash Flood Warning for...
Western Clinton County in south central Illinois...
Southern Madison County in southwestern Illinois...
Northwestern Monroe County in southwestern Illinois...
Saint Clair County in southwestern Illinois...
Northeastern Jefferson County in east central Missouri...
Eastern Saint Louis County in east central Missouri...
East Central Saint Louis City in east central Missouri...
* Until 900 PM CDT.
* At 506 PM CDT, Doppler radar indicated thunderstorms producing
heavy rain across the warned area. Between 1 and 2 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 caused by thunderstorms.
SOURCE...Radar indicated.
IMPACT...Flash flooding of small creeks and streams, urban areas,
highways, streets and underpasses as well as other poor
drainage and low-lying areas.
* Some locations that will experience flash flooding include...
Belleville, Granite City, O'Fallon, East St. Louis, Collinsville,
Edwardsville, Fairview Heights, Cahokia, Swansea, Glen Carbon,
Shiloh, Highland, Troy, Waterloo, Columbia, Maryville, Mascoutah,
Pontoon Beach and Centreville.
This includes the following State Parks...
Frank Holten State Park and Horseshoe Lake State Park.
This includes the following highways...
Interstate 64 in Illinois between exits 9 and 27. Interstate 70 in
Illinois between exits 21 and 30.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 3826 9037 3835 9036 3844 9029 3852 9026
3861 9018 3867 9018 3872 9021 3877 9017
3882 8960 3866 8960 3866 8971 3843 8970
3821 9035
FLASH FLOOD...RADAR INDICATED
$$
Walsh2 follow-up statements
615
WGUS73 KLSX 190109
FFSLSX
Flash Flood Statement
National Weather Service St Louis MO
809 PM CDT Mon May 18 2026
MOC510-190119-
/O.CAN.KLSX.FF.W.0020.000000T0000Z-260519T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Saint Louis City MO-
809 PM CDT Mon May 18 2026
...FLASH FLOOD WARNING IS CANCELLED FOR THE EAST CENTRAL SAINT LOUIS
CITY...
Flooding is no longer expected to pose a threat. Please continue to
heed remaining road closures.
A Flood Watch remains in effect until 100 PM CDT Tuesday for portions
of southwest Illinois and east central Missouri.
A Flood Watch remains in effect until 100 PM CDT Tuesday for a
portion of south central Illinois.
&&
LAT...LON 3826 9037 3835 9036 3844 9029 3852 9026
3861 9018 3867 9018 3872 9021 3875 9018
3876 9018 3877 9017 3882 8960 3866 8960
3866 8971 3843 8970 3821 9035
$$
ILC027-119-133-163-MOC099-189-190200-
/O.CON.KLSX.FF.W.0020.000000T0000Z-260519T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Clinton IL-Madison IL-Monroe IL-Saint Clair IL-Jefferson MO-Saint
Louis MO-
809 PM CDT Mon May 18 2026
...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 9 PM CDT THIS EVENING
FOR WESTERN CLINTON COUNTY IN SOUTH CENTRAL ILLINOIS, SOUTHERN
MADISON, NORTHWESTERN MONROE AND SAINT CLAIR COUNTIES IN SOUTHWESTERN
ILLINOIS AND NORTHEASTERN JEFFERSON AND EASTERN SAINT LOUIS COUNTIES
IN EAST CENTRAL MISSOURI...
At 809 PM CDT, Doppler radar indicated thunderstorms producing heavy
rain across the warned area. Between 1 and 2 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 caused by thunderstorms.
SOURCE...Radar indicated.
IMPACT...Flash flooding of small creeks and streams, urban areas,
highways, streets and underpasses as well as other poor
drainage and low-lying areas.
Some locations that will experience flash flooding include...
Belleville, Granite City, O'Fallon, East St. Louis, Collinsville,
Edwardsville, Fairview Heights, Cahokia, Swansea, Glen Carbon,
Shiloh, Highland, Troy, Waterloo, Columbia, Maryville, Mascoutah,
Pontoon Beach and Centreville.
This includes the following State Parks...
Frank Holten State Park and Horseshoe Lake State Park.
This includes the following highways...
Interstate 64 in Illinois between exits 9 and 27. Interstate 70 in
Illinois between exits 21 and 30.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 3826 9037 3835 9036 3844 9029 3852 9026
3861 9018 3867 9018 3872 9021 3875 9018
3876 9018 3877 9017 3882 8960 3866 8960
3866 8971 3843 8970 3821 9035
FLASH FLOOD...RADAR INDICATED
$$
Maples163
WGUS73 KLSX 190157
FFSLSX
Flash Flood Statement
National Weather Service St Louis MO
857 PM CDT Mon May 18 2026
ILC027-119-133-163-MOC099-189-190207-
/O.CAN.KLSX.FF.W.0020.000000T0000Z-260519T0200Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Clinton IL-Madison IL-Monroe IL-Saint Clair IL-Jefferson MO-Saint
Louis MO-
857 PM CDT Mon May 18 2026
...FLASH FLOOD WARNING IS CANCELLED FOR WESTERN CLINTON COUNTY IN
SOUTH CENTRAL ILLINOIS, SOUTHERN MADISON, NORTHWESTERN MONROE AND
SAINT CLAIR COUNTIES IN SOUTHWESTERN ILLINOIS AND NORTHEASTERN
JEFFERSON AND EASTERN SAINT LOUIS COUNTIES IN EAST CENTRAL
MISSOURI...
The heavy rain has ended. Minor flooding may continue to linger for
the next few hours, especially in flood prone areas. Please continue
to heed remaining road closures.
A Flood Watch remains in effect until 100 PM CDT Tuesday for portions
of southwest Illinois and east central Missouri.
A Flood Watch remains in effect until 100 PM CDT Tuesday for a
portion of south central Illinois.
&&
LAT...LON 3826 9037 3835 9036 3844 9029 3852 9026
3861 9018 3867 9018 3872 9021 3875 9018
3876 9018 3877 9017 3882 8960 3866 8960
3866 8971 3843 8970 3821 9035
$$
MaplesThe office that day
Everything else NWS St. Louis, MO issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 18, 1:12 AM CDT | Flood Watch | LSX | Audrain, Boone, Callaway, Cole, Crawford, Franklin and 14 more | 35 hr |
| May 18, 6:12 AM CDT | Severe Thunderstorm Warning | LSX | Audrain, Marion, Pike, Ralls | 48 min |
| May 18, 6:18 AM CDT | Severe Thunderstorm Warning | LSX | Audrain, Boone, Callaway | 42 min |
| May 18, 6:41 AM CDT | Tornado Warning | LSX | Pike, Ralls | 28 min |
| May 18, 7:21 AM CDT | Severe Thunderstorm Warning | LSX | Lincoln, Pike | 39 min |
| May 18, 10:56 AM CDT | Areal Flood Advisory | LSX | Franklin, Gasconade | 4 hr |
| May 18, 12:39 PM CDT | Areal Flood Advisory | LSX | Crawford, Franklin, Washington | 7 hr |
| May 18, 1:22 PM CDT | Areal Flood Advisory | LSX | Saint Louis, City of Saint Louis | 6 hr |
| May 18, 2:40 PM CDT | Areal Flood Advisory | LSX | Boone, Callaway, Cole, Moniteau | 4 hr |
| May 18, 3:05 PM CDT | Flash Flood Warning | LSX | Crawford, Franklin, Gasconade, Warren | 6 hr |
| May 18, 5:01 PM CDT | Flash Flood Warning | LSX | Franklin, Gasconade, Warren | 3 hr |
| May 18, 5:12 PM CDT | Flash Flood Warning | LSX | Saint Charles, Saint Louis, City of Saint Louis | 3 hr |
| May 18, 7:37 AM CDT | Severe Thunderstorm Warning | LSX | Calhoun, Greene, Pike | 25 min |
| May 18, 11:25 AM CDT | Areal Flood Advisory | LSX | Fayette, Marion | 3 hr |
| May 18, 2:00 PM CDT | Areal Flood Advisory | LSX | Madison, Monroe, Saint Clair | 3 hr |
| May 18, 2:11 PM CDT | Flash Flood Warning | LSX | Clinton, Fayette, Marion | 6 hr |
| May 18, 2:13 PM CDT | Areal Flood Advisory | LSX | Bond, Clinton, Fayette, Washington | 41 min |
| May 18, 2:54 PM CDT | Flash Flood Warning | LSX | Bond, Clinton, Fayette, Madison, Marion, Saint Clair and 1 more | 6 hr |
Nearby
Flash Flood Warnings in Illinois, 2026Flash Flood Warnings in Missouri, 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.