Alert archive / Iowa / Flash Flood Warnings in 2025
Flash Flood Warning 21, NWS Sioux Falls, SD
NWS Sioux Falls, SD issued this flash flood warning at Aug 18, 2025, 3:36 AM CDT for Lyon County, Osceola County, Sioux County, Iowa. It was in force for 2 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
- Aug 18, 2025, 3:36 AM CDT (08:36 UTC)
- Expired
- Aug 18, 2025, 5:39 AM CDT
- In force
- 2 hr
- Issued by
- NWS Sioux Falls, SD
- Area
- Storm-based polygon
- Flood severity
- None
Counties Lyon County, IA, Osceola County, IA, Sioux County, IA
The radar
The Sioux Falls radar (KFSD), 66 km from the middle of the area, began a volume at 08:36 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
Omaha, NE (KOAX), launched 00:00Z, 8.6 hours before the alert went out and 229 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
- 2562 J/kg
- Mixed-layer CIN
- -21 J/kg
- Mixed-layer LCL
- 1384 m above ground
- 0-6 km bulk shear
- 17 kt
- 0-1 km storm-relative helicity
- 30 m²/s²
- 0-3 km storm-relative helicity
- 116 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
148
WGUS53 KFSD 180836
FFWFSD
IAC119-143-167-181145-
/O.NEW.KFSD.FF.W.0021.250818T0836Z-250818T1145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Sioux Falls SD
336 AM CDT Mon Aug 18 2025
The National Weather Service in Sioux Falls has issued a
* Flash Flood Warning for...
Eastern Lyon County in northwestern Iowa...
West Central Osceola County in northwestern Iowa...
Northeastern Sioux County in northwestern Iowa...
* Until 645 AM CDT.
* At 336 AM CDT, Doppler radar indicated thunderstorms producing
heavy rain across the warned area. Between 2 and 4 inches of rain
have fallen. The expected rainfall rate is 3 to 5 inches in 1
hour. Additional rainfall amounts of 0.5 to 1 inch are possible in
the warned area. Flash flooding is ongoing or expected to begin
shortly.
HAZARD...Flash flooding caused by thunderstorms.
SOURCE...Radar.
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...
George, Little Rock and Matlock.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 4346 9604 4343 9576 4326 9591 4322 9594
4334 9617
FLASH FLOOD...RADAR INDICATED
EXPECTED RAINFALL RATE...3-5 INCHES IN 1 HOUR
$$
JM1 follow-up statement
115
WGUS73 KFSD 181039
FFSFSD
Flash Flood Statement
National Weather Service Sioux Falls SD
539 AM CDT Mon Aug 18 2025
IAC119-143-167-181049-
/O.CAN.KFSD.FF.W.0021.000000T0000Z-250818T1145Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Lyon IA-Osceola IA-Sioux IA-
539 AM CDT Mon Aug 18 2025
...FLASH FLOOD WARNING IS CANCELLED FOR EASTERN LYON, WEST CENTRAL
OSCEOLA AND NORTHEASTERN SIOUX COUNTIES...
Flooding is no longer expected to pose a threat. Please continue to
heed remaining road closures.
&&
LAT...LON 4346 9604 4343 9576 4326 9591 4322 9594
4334 9617
$$
JMNearby
Flash Flood Warnings in Iowa, 2025Every flash flood warning in 2025
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.