Alert archive / Iowa / Flash Flood Warnings in 1998

Flash Flood Warning 29, NWS Des Moines, IA

July 6, 1998Polk County, Iowa

NWS Des Moines, IA issued this flash flood warning at Jul 6, 1998, 9:21 PM CDT for Polk County, Iowa. It was in force for 6 hr. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued
Jul 6, 1998, 9:21 PM CDT (02:21 UTC)
Expired
Jul 7, 1998, 3:25 AM CDT
In force
6 hr
Issued by
NWS Des Moines, IA
Area
Whole counties

County Polk County, IA

The radar

The Des Moines radar (KDMX), 13 km from the middle of the area, began a volume at 02:20 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, 2.4 hours before the alert went out and 236 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 1998-07-07Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 5400 joules per kilogram.LCLEL10008507005003002001001 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 1998-07-07The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 77 square meters per square second.19395878Sfc1 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
5400 J/kg
Mixed-layer CIN
-6 J/kg
Mixed-layer LCL
1040 m above ground
0-6 km bulk shear
39 kt
0-1 km storm-relative helicity
77 m²/s²
0-3 km storm-relative helicity
110 m²/s²
Significant tornado parameter
3.7
Supercell composite
14.8

Open this sounding in Storm Lab

The text

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

000 
TTAA00 KDSM 070221
FFWDSM
IAC153-070825-

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE DES MOINES IA
921 PM CDT MON JUL 6 1998

THE NATIONAL WEATHER SERVICE IN DES MOINES HAS ISSUED A

* FLASH FLOOD WARNING FOR...
  POLK COUNTY IN CENTRAL IOWA

* UNTIL 325 AM CDT

* AT 920 PM CDT... NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
  THUNDERSTORM WITH VERY HEAVY RAIN WESTERN POLK COUNTY FROM WEST DES
  MOINES TO JOHNSTON... MOVING EAST AT 20 MPH.

* OVER 3 INCHES OF RAINFALL IS LIKELY ACROSS POLK COUNTY BY 1030 PM.
  THIS WILL CAUSE FLASH FLOODING IN URBAN AREAS AND MANY STREAMS WILL
  LIKELY GO OUT OF THEIR BANKS.  WALNUT CREEK WILL BE AFFECTED BY THE
  HEAVY RAINFALL.

SLOME STREAMS AFFECTED INCLUDE...
  WALNUT CREEK
  FOUR MILE
  JORDAN
  BEAVER CREEK

DON'T DRIVE INTO AREAS WHERE WATER COVERS THE ROAD!

JOHNSON

What forecasters said that day

The local office's own words before this flash flood warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

In the hours before

Special weather statement, Jul 6, 4:42 PM CDT, 4 hours 39 minutes before
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-071100-

CENTRAL IOWA THUNDERSTORM OUTLOOK
NATIONAL WEATHER SERVICE DES MOINES IA
442 PM CDT MON JUL 6 1998

HAZARD--WIDESPREAD HEAVY RAIN OF 1 TO 3 INCHES AND ISOLATED AMOUNTS
UP TO 5. A FEW STORMS COULD ALSO PRODUCE WIND GUSTS TO 80 MPH AND
HAIL UP TO GOLFBALL SIZE.

AREA OF CONCERN--ALL OF CENTRAL IOWA.

TIMING DETAILS--THE HEAVY RAIN THREAT WILL LAST ALL NIGHT AND INTO
TUESDAY MORNING. THE SEVERE WEATHER THREAT WILL BE HIGHEST BETWEEN
800 PM AND 300 AM.

METEOROLOGICAL COMMENTS--A THUNDERSTORM COMPLEX HAS ALREADY
DEVELOPED OVER NORTHEAST NEBRASKA AND SOUTHEAST SOUTH DAKOTA THIS
AFTERNOON WITH NUMEROUS SEVERE THUNDERSTORM WARNINGS IN EFFECT.
WIND GUSTS UP TO 70 MPH AND 1 INCH DIAMETER HAIL HAVE ALREADY BEEN
REPORTED. THIS COMPLEX WILL MOVE INTO IOWA AFTER DARK AS IT FEEDS ON
EXTREMELY HIGH MOISTURE VALUES THROUGHOUT THE ATMOSPHERE.
PRECIPITABLE WATERS WERE APPROACHING 2 INCHES THIS AFTERNOON WITH
SURFACE DEWPOINTS APPROACHING 80 DEGREES. AS THE NIGHT WEARS ON THE
THUNDERSTORMS SHOULD BECOME WEAKER...BUT THEY WILL ALSO BEGIN TO
TRAIN ALONG AN EAST-WEST STATIONARY FRONT STUCK RIGHT OVER THE
HEART OF IOWA.

PRECAUTIONS--A FLASH FLOOD WATCH IS ALREADY IN EFFECT FOR THE ENTIRE
STATE...AND SEVERE THUNDERSTORM WATCHES MAY BE REQUIRED LATER THIS
EVENING. SPOTTER ACTIVATION IS A NEAR CERTAINTY TONIGHT...ESPECIALLY
IN THE NORTHWEST HALF OF THE STATE WHERE THE STORMS WILL LIKELY BE AT
THEIR STRONGEST LATE THIS EVENING.

PYTLAK
Special weather statement, Jul 6, 4:58 PM CDT, 4 hours 23 minutes before
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-081>086-
092>097-071100-

CENTRAL IOWA THUNDERSTORM OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
458 PM CDT MON JUL 6 1998

HAZARD--WIDESPREAD HEAVY RAIN OF 1 TO 3 INCHES AND ISOLATED AMOUNTS
UP TO 5. A FEW STORMS COULD ALSO PRODUCE WIND GUSTS TO 80 MPH AND
HAIL UP TO GOLFBALL SIZE.

AREA OF CONCERN--ALL OF CENTRAL IOWA.

TIMING DETAILS--THE HEAVY RAIN THREAT WILL LAST ALL NIGHT AND INTO
TUESDAY MORNING. THE SEVERE WEATHER THREAT WILL BE HIGHEST BETWEEN
800 PM AND 300 AM.

METEOROLOGICAL COMMENTS--A THUNDERSTORM COMPLEX HAS ALREADY
DEVELOPED OVER NORTHEAST NEBRASKA AND SOUTHEAST SOUTH DAKOTA THIS
AFTERNOON WITH NUMEROUS SEVERE THUNDERSTORM WARNINGS IN EFFECT.
WIND GUSTS UP TO 70 MPH AND 1 INCH DIAMETER HAIL HAVE ALREADY BEEN
REPORTED. THIS COMPLEX WILL MOVE INTO IOWA AFTER DARK AS IT FEEDS ON
EXTREMELY HIGH MOISTURE VALUES THROUGHOUT THE ATMOSPHERE.
PRECIPITABLE WATERS WERE APPROACHING 2 INCHES THIS AFTERNOON WITH
SURFACE DEWPOINTS APPROACHING 80 DEGREES. AS THE NIGHT WEARS ON THE
THUNDERSTORMS SHOULD BECOME WEAKER...BUT THEY WILL ALSO BEGIN TO
TRAIN ALONG AN EAST-WEST STATIONARY FRONT STUCK RIGHT OVER THE
HEART OF IOWA.

PRECAUTIONS--A FLASH FLOOD WATCH IS ALREADY IN EFFECT FOR THE ENTIRE
STATE...AND A TORNADO WATCH WILL BE ISSUED FOR NORTHWEST IOWA SHORTLY.
SPOTTER ACTIVATION IS A NEAR CERTAINTY TONIGHT...ESPECIALLY IN THE
NORTHWEST HALF OF THE STATE WHERE THE STORMS WILL LIKELY BE AT
THEIR STRONGEST LATE THIS EVENING.

PYTLAK
UPDATED TO MENTION IMPENDING TORNADO WATCH IN NORTHWEST IOWA
Special weather statement, Jul 6, 8:44 PM CDT, 37 minutes before
IAZ004-005-015-023-024-033-034-044-045-070340-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
844 PM CDT MON JUL 6 1998

...TORNADO WATCH HAS BEEN CANCELLED FOR PARTS OF WEST CENTRAL AND
NORTHWEST IOWA...

THE TORNADO WATCH THAT WAS IN EFFECT FOR PARTS OF WEST CENTRAL AND
NORTHWEST IOWA IS NO LONGER IN EFFECT. THE STRONGEST THUNDERSTORMS
HAVE SHIFTED SOUTHEAST OF THE AREA AN NO LONGER POSE A THREAT TO THE
AREA. THUNDERSTORMS WILL CONTINUE INTERMITTANTLY DURING THE NIGHT
BUT THE THREAT OF WIDESPREAD SEVERE WEATHER HAS ENDED.

SMITH
Special weather statement, Jul 6, 8:44 PM CDT, 37 minutes before
IAZ004-005-015-023-024-033-034-044-045-070340-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE DES MOINES IA
844 PM CDT MON JUL 6 1998

...TORNADO WATCH HAS BEEN CANCELLED FOR PARTS OF WEST CENTRAL AND
NORTHWEST IOWA...

THE TORNADO WATCH THAT WAS IN EFFECT FOR PARTS OF WEST CENTRAL AND
NORTHWEST IOWA IS NO LONGER IN EFFECT. THE STRONGEST THUNDERSTORMS
HAVE SHIFTED SOUTHEAST OF THE AREA AN NO LONGER POSE A THREAT TO THE
AREA. THUNDERSTORMS WILL CONTINUE INTERMITTANTLY DURING THE NIGHT
BUT THE THREAT OF WIDESPREAD SEVERE WEATHER HAS ENDED.

SMITH

The office that day

Everything else NWS Des Moines, IA issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jul 6, 7:22 PM CDTTornado WarningDMXCarroll33 min
Jul 6, 8:15 PM CDTSevere Thunderstorm WarningDMXDallas, Guthrie35 min
Jul 6, 8:46 PM CDTFlash Flood WarningDMXDallas3 hr
Jul 6, 8:54 PM CDTSevere Thunderstorm WarningDMXDallas, Polk36 min
Jul 6, 9:14 PM CDTFlash Flood WarningDMXGuthrie6 hr
Jul 6, 9:20 PM CDTSevere Thunderstorm WarningDMXStory35 min
Jul 6, 9:29 PM CDTSevere Thunderstorm WarningDMXJasper, Polk46 min
Jul 6, 9:35 PM CDTTornado WarningDMXPolk35 min
Jul 6, 9:45 PM CDTSevere Thunderstorm WarningDMXMarion, Warren45 min
Jul 6, 10:00 PM CDTTornado WarningDMXMarion35 min
Jul 6, 10:15 PM CDTSevere Thunderstorm WarningDMXJasper35 min
Jul 6, 10:37 PM CDTSevere Thunderstorm WarningDMXMarion33 min
Jul 6, 11:41 PM CDTFlash Flood WarningDMXDallas3 hr

Nearby

Flash Flood Warnings in Iowa, 1998Every flash flood warning in 1998

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.