Alert archive / Iowa / Flash Flood Warnings in 2012

Flash Flood Warning 2, NWS Sioux Falls, SD

May 1, 2012Lyon County, Iowa

NWS Sioux Falls, SD issued this flash flood warning at May 1, 2012, 8:40 PM CDT for Lyon County, Iowa. 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
May 1, 2012, 8:40 PM CDT (01:40 UTC)
Expired
May 1, 2012, 11:18 PM CDT
In force
3 hr
Issued by
NWS Sioux Falls, SD
Area
Storm-based polygon
Flood severity
None

County Lyon County, IA

The radar

The Sioux Falls radar (KFSD), 61 km from the middle of the area, began a volume at 01:39 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

TimeReportWhereRemark
May 1, 10:00 PM CDTHEAVY RAIN 012 E Rock Rapids, IA2.92 INCHES OF RAINFALL
May 1, 10:00 PM CDTHEAVY RAIN 2.9212 E Rock Rapids, IA2.92 INCHES OF RAIN

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Omaha, NE (KOAX), launched 00:00Z, 1.7 hours before the alert went out and 228 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.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2012-05-02Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1502 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Omaha, NE at 00:00Z on 2012-05-02The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 75 square meters per square second.193958Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
1502 J/kg
Mixed-layer CIN
-30 J/kg
Mixed-layer LCL
1477 m above ground
0-6 km bulk shear
36 kt
0-1 km storm-relative helicity
75 m²/s²
0-3 km storm-relative helicity
122 m²/s²
Significant tornado parameter
0.4
Supercell composite
5.2

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

244 
WGUS53 KFSD 020140
FFWFSD
IAC119-020430-
/O.NEW.KFSD.FF.W.0002.120502T0140Z-120502T0430Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE SIOUX FALLS SD
840 PM CDT TUE MAY 1 2012

THE NATIONAL WEATHER SERVICE IN SIOUX FALLS HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  EASTERN LYON COUNTY IN NORTHWEST IOWA

* UNTIL 1130 PM CDT

* AT 835 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
  THUNDERSTORMS WITH VERY HEAVY RAINFALL ACROSS THE WARNED AREA.  
  HEAVY RAIN OF 1 TO 2 INCHES HAVE ALREADY FALLEN OVER PORTIONS OF 
  THE COUNTY...WITH AN ADDITIONAL 1 TO 2 INCHES LIKELY. 

* RUNOFF FROM THIS EXCESSIVE RAINFALL WILL CAUSE FLASH FLOODING TO
  OCCUR. SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE...ROCK
  RAPIDS...ALVORD...DOON...GEORGE AND LITTLE ROCK.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...HIGHWAYS AND UNDERPASSES. ADDITIONALLY...COUNTRY
ROADS AND FARMLANDS ALONG THE BANKS OF CREEKS...STREAMS AND OTHER LOW
LYING AREAS ARE SUBJECT TO FLOODING.

&&

LAT...LON 4326 9587 4326 9633 4350 9631 4350 9586

$$

CJ
1 follow-up statement
846 
WGUS73 KFSD 020418
FFSFSD

FLASH FLOOD STATEMENT
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1118 PM CDT TUE MAY 1 2012

IAC119-020433-
/O.CAN.KFSD.FF.W.0002.000000T0000Z-120502T0430Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
LYON IA-
1118 PM CDT TUE MAY 1 2012

...THE FLASH FLOOD WARNING THAT WAS IN EFFECT FOR EASTERN LYON COUNTY
IS CANCELLED...

EXCESS RUNOFF FROM HEAVY RAIN HAS ENDED OVER THE WARNED AREA. STREAMS
AND CREEKS IN THE WARNED AREA HAVE RECEDED OR WERE BEGINNING TO
RECEDE...ENDING THE FLOOD THREAT. IF FLOODING HAS BEEN OBSERVED...
PLEASE REPORT IT TO YOUR LOCAL LAW ENFORCEMENT AGENCY.

LAT...LON 4326 9587 4326 9633 4350 9631 4350 9586

$$

CJ

The office that day

Everything else NWS Sioux Falls, SD issued on the same UTC day.

IssuedProductOfficeCountiesLasted
May 1, 7:12 PM CDTSevere Thunderstorm WarningFSDLyon, Sioux33 min
May 1, 7:27 PM CDTTornado WarningFSDLyon, Sioux33 min
May 1, 7:41 PM CDTSevere Thunderstorm WarningFSDLyon, Sioux34 min
May 1, 7:57 PM CDTTornado WarningFSDLyon33 min
May 1, 8:09 PM CDTSevere Thunderstorm WarningFSDLyon36 min
May 1, 9:15 PM CDTSevere Thunderstorm WarningFSDBuena Vista, Cherokee, Clay, O'Brien, Plymouth, Sioux30 min
May 1, 9:22 PM CDTSevere Thunderstorm WarningFSDDickinson, Osceola38 min
May 1, 9:29 PM CDTTornado WarningFSDClay, O'Brien46 min
May 1, 9:41 PM CDTSevere Thunderstorm WarningFSDBuena Vista, Cherokee, Clay, Dickinson, O'Brien, Osceola34 min
May 1, 9:44 PM CDTTornado WarningFSDClay31 min
May 1, 10:13 PM CDTSevere Thunderstorm WarningFSDBuena Vista, Clay, Dickinson17 min

Nearby

Flash Flood Warnings in Iowa, 2012Every flash flood warning in 2012

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.