Alert archive / Iowa / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 111, NWS Des Moines, IA

August 30, 20215 counties in Iowa

NWS Des Moines, IA issued this severe thunderstorm warning at Aug 30, 2021, 11:29 PM CDT for 5 counties in Iowa. It was in force for 46 min. 4 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
Aug 30, 2021, 11:29 PM CDT (04:29 UTC)
Expired
Aug 31, 2021, 12:15 AM CDT
In force
46 min
Issued by
NWS Des Moines, IA
Area
Storm-based polygon
Hail
0.75 in
Wind
60.0 mph

Counties Boone County, IA, Dallas County, IA, Marshall County, IA, Polk County, IA, Story County, IA

The radar

The Des Moines radar (KDMX), 19 km from the middle of the area, began a volume at 04:18 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
Aug 30, 11:42 PM CDTTSTM WND GST 601 Wnw Polk City, IANWS EMPLOYEE REPORTS WIND GUSTS NEAR 60 MPH IN POLK CITY. BRANCHES DOWN.
Aug 30, 11:51 PM CDTTSTM WND DMG3 Ese Windsor Heights, IALARGE TREE DOWN ACROSS THE ROAD. TIME ESTIMATED FROM KOAX RADAR.
Aug 30, 11:53 PM CDTTSTM WND GST 602 Ese Waukee, IAESTIMATED 60 TO 65 MPH WIND.
Aug 31, 12:17 AM CDTTSTM WND DMG1 Ese Windsor Heights, IAWIRES DOWN NEAR 55TH AND UNIVERSITY.

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, 4.5 hours before the alert went out and 244 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 2021-08-31Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1443 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 2021-08-31The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 4 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
1443 J/kg
Mixed-layer CIN
-31 J/kg
Mixed-layer LCL
1305 m above ground
0-6 km bulk shear
35 kt
0-1 km storm-relative helicity
4 m²/s²
0-3 km storm-relative helicity
143 m²/s²
Significant tornado parameter
0.3
Supercell composite
3.5

Open this sounding in Storm Lab

The text

As transmitted.

189 
WUUS53 KDMX 310429
SVRDMX
IAC015-049-127-153-169-310515-
/O.NEW.KDMX.SV.W.0111.210831T0429Z-210831T0515Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Des Moines IA
1129 PM CDT Mon Aug 30 2021

The National Weather Service in Des Moines  has issued a

* Severe Thunderstorm Warning for...
  Polk County in central Iowa...
  Story County in central Iowa...
  Southwestern Marshall County in central Iowa...
  Southeastern Boone County in central Iowa...
  Eastern Dallas County in central Iowa...

* Until 1215 AM CDT.

* At 1129 PM CDT, a severe thunderstorm was located over Slater, or 9
  miles north of Ankeny, moving southeast at 35 mph.

  HAZARD...60 mph wind gusts and penny size hail.

  SOURCE...Radar indicated.

  IMPACT...Expect damage to roofs, siding, and trees.

* This severe thunderstorm will be near...
  Saylorville around 1140 PM CDT.

Other locations in the path of this severe thunderstorm include
Ankeny and Bondurant.

This includes the following highways...
 Interstate 35 between mile markers 68 and 72, and between mile
markers 87 and 120.
 Interstate 80 between mile markers 116 and 139.
 Interstate 235 between mile markers 1 and 8, and between mile
markers 13 and 14.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4186 9328 4186 9335 4181 9335 4151 9371
      4151 9386 4168 9410 4217 9351 4195 9317
TIME...MOT...LOC 0429Z 309DEG 29KT 4186 9365 

HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...0.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

REV
2 follow-up statements
236 
WWUS53 KDMX 310447
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
1147 PM CDT Mon Aug 30 2021

IAC015-049-127-153-169-310515-
/O.CON.KDMX.SV.W.0111.000000T0000Z-210831T0515Z/
Polk IA-Story IA-Marshall IA-Boone IA-Dallas IA-
1147 PM CDT Mon Aug 30 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1215 AM CDT
FOR POLK...STORY...SOUTHWESTERN MARSHALL...SOUTHEASTERN BOONE AND
EASTERN DALLAS COUNTIES...

At 1146 PM CDT, a severe thunderstorm was located over Bondurant, or
near Altoona, moving southeast at 15 mph.

HAZARD...60 mph wind gusts and penny size hail.

SOURCE...Trained weather spotters reported 60 mph wind gusts in 
Polk City at 1142 PM CDT.

IMPACT...Expect damage to roofs, siding, and trees.

Locations impacted include...
  Bondurant.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4186 9328 4186 9335 4181 9335 4151 9371
      4151 9386 4168 9410 4217 9351 4195 9317
TIME...MOT...LOC 0446Z 312DEG 11KT 4172 9348 

HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...0.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

REV
546 
WWUS53 KDMX 310510
SVSDMX

Severe Weather Statement
National Weather Service Des Moines IA
1210 AM CDT Tue Aug 31 2021

IAC015-049-127-153-169-310519-
/O.EXP.KDMX.SV.W.0111.000000T0000Z-210831T0515Z/
Polk IA-Story IA-Marshall IA-Boone IA-Dallas IA-
1210 AM CDT Tue Aug 31 2021

...THE SEVERE THUNDERSTORM WARNING FOR NORTHERN and CENTRAL 
POLK...STORY...SOUTHWESTERN MARSHALL...SOUTHEASTERN BOONE AND 
EASTERN DALLAS COUNTIES WILL EXPIRE
AT 1215 AM CDT...
        
The storm which prompted the warning has moved out of the area.
Therefore, the warning will be allowed to expire.  However gusty
winds and heavy rain are still possible with this thunderstorm.

A SEVERE THUNDERSTORM WARNING remains in effect for Southeast Polk 
County and areas to the east and southeast until 1230 AM CDT.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
Des Moines .

LAT...LON 4186 9328 4186 9335 4181 9335 4151 9371
      4151 9386 4168 9410 4217 9351 4195 9317
TIME...MOT...LOC 0509Z 309DEG 29KT 4161 9330 

$$

REV

The office that day

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

IssuedProductOfficeCountiesLasted
Aug 30, 9:58 PM CDTSevere Thunderstorm WarningDMXCarroll, Crawford, Sac62 min
Aug 30, 10:50 PM CDTSevere Thunderstorm WarningDMXCarroll, Crawford55 min
Aug 30, 10:58 PM CDTSevere Thunderstorm WarningDMXAudubon, Carroll, Crawford, Greene, Guthrie62 min
Aug 30, 11:50 PM CDTSevere Thunderstorm WarningDMXJasper, Marshall40 min
Aug 30, 11:54 PM CDTSevere Thunderstorm WarningDMXJasper, Madison, Marion, Polk, Warren36 min
Aug 31, 12:07 AM CDTSevere Thunderstorm WarningDMXAdair, Audubon, Cass, Guthrie38 min
Aug 31, 12:35 AM CDTSpecial Weather StatementDMXClarke, Lucas, Madison, Marion, Union, Warren70 min
Aug 31, 9:16 AM CDTAreal Flood WarningDMXBlack Hawk2 hr

Nearby

Severe Thunderstorm Warnings in Iowa, 2021Every severe thunderstorm warning in 2021

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.