Tornadoes · United States · Iowa · 2004

F1 tornado, Marshall County, Iowa, August 3, 2004

This F1 tornado ran 5.0 miles across Marshall County on August 3, 2004, touching down at 5:20 PM CDT and reaching 100 yards wide. It killed nobody, and did $100,000 of property damage.

The rating scale

Tracks are drawn in the color of the rating. The Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

  1. F040 to 72 mph

    Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

  2. F173 to 112 mphthis tornado

    Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

  3. F2113 to 157 mph

    Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

  4. F3158 to 206 mph

    Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

  5. F4207 to 260 mph

    Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

  6. F5261 to 318 mph

    Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

  7. Unrated

    The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

The record

Rating
F1
Date
August 3, 2004
Touchdown
5:20 PM CDT (22:20 UTC)
Path length
5.0 miles (8.0 km)
Path width
100 yards (91 m)
Deaths
0
Injuries
0
Property damage
$100,000
County
Marshall County
Touchdown point
42.120, -93.000
Lift-off point
42.120, -92.900
Record number
1453

The warnings

18 minutes of warning. NWS DMX issued a tornado warning for this county at 22:02 UTC, 18 minutes before the tornado touched down, in force until 22:45 UTC.

Issued (UTC)ExpiredProductOffice
21:52 UTC22:45 UTCSevere Thunderstorm WarningDMX
22:02 UTC22:45 UTCTornado WarningDMX

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The forecast that day

The Storm Prediction Center had this point in a Moderate Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 20:02 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The air that afternoon

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

Davenport, (KDVN), 12:00Z

10.3 hours before the tornado, 210 km from the path. August 3, 2004.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2004-08-03Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 760 joules per kilogram, CIN -200, lifted condensation level 1021 meters above ground. Wind barbs in knots down the right edge.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. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Davenport, at 12:00Z on 2004-08-03The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity -1 square meters per square second, 0 to 6 km bulk shear 31 knots.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. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
760 J/kg
Mixed-layer CIN
-200 J/kg
Surface CAPE
0 J/kg
Mixed-layer LCL
1021 m above ground
0-6 km bulk shear
31 kt
0-1 km bulk shear
3 kt
0-1 km storm-relative helicity
-1 m²/s²
0-3 km storm-relative helicity
16 m²/s²
Significant tornado parameter
0.0
Supercell composite
-0.1
0-3 km lapse rate
3.0 K/km

Open this sounding in Storm Lab

Davenport, (KDVN), 00:00Z

1.7 hours after it, 210 km from the path. August 4, 2004.

Skew-T log-pSkew-T log-p diagram, Davenport, at 00:00Z on 2004-08-04Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 2771 joules per kilogram, CIN -73, lifted condensation level 1163 meters above ground. Wind barbs in knots down the right edge.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. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Davenport, at 00:00Z on 2004-08-04The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 54 square meters per square second, 0 to 6 km bulk shear 35 knots.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. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
2771 J/kg
Mixed-layer CIN
-73 J/kg
Surface CAPE
4814 J/kg
Mixed-layer LCL
1163 m above ground
0-6 km bulk shear
35 kt
0-1 km bulk shear
8 kt
0-1 km storm-relative helicity
54 m²/s²
0-3 km storm-relative helicity
163 m²/s²
Significant tornado parameter
1.6
Supercell composite
16.5
0-3 km lapse rate
6.7 K/km

Open this sounding in Storm Lab

The radar

The Des Moines radar (KDMX), 77 km away, was scanning. The volume nearest the touchdown began at 22:18 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)ReportWhereCountyRemark
21:18 UTCTSTM WND GST 80Iowa FallsHardin, IABRANCHES AND POWER LINES DOWN IN IOWA FALLS.
21:24 UTCTSTM WND GST 65Iowa FallsHardin, IA
21:40 UTCTSTM WND DMGNw ZearingStory, IAROADS CLOSED JUST NORTH OF ZEARING DUE TO DOWNED TREES.
21:47 UTCTSTM WND DMGRadcliffeHardin, IAROOF DAMAGE TO HOUSE. NUMEROUS TREES DOWN.
21:50 UTCTSTM WND DMGEldoraHardin, IATREES DOWN IN ELDORA BLOCKING ROADS WITH STANDING WATER.
21:50 UTCTSTM WND DMGRolandStory, IA12 INCH DIAMETER TREES AND LIMBS DOWN.
21:53 UTCTORNADO8 Sw HubbardHardin, IABRIEF TOUCHDOWN. MOVED A CAMPER.
21:55 UTCTSTM WND DMGMccallsburgStory, IANUMEROUS TWELVE INCH DIAMTER TREES DOWN.
21:55 UTCTORNADO6 S RadcliffeHardin, IATORNADO TOUCHDOWN. OUT BUILDINGS AND HOUSE DAMAGED. NO INJURIES.
22:00 UTCTSTM WND DMG20 E Story CityMarshall, IA12 INCH DIAMETER TREE LIMBS DOWN IN MACCALLSBURG.
22:27 UTCTSTM WND GST 65MarshalltownMarshall, IASEVERAL 12 INCH DIAMETER TREES AND POWER LINES DOWN IN MARSHALLTOWN.
22:30 UTCTSTM WND DMGAlbionMarshall, IANUMEROUS TREES DOWN.
22:30 UTCTSTM WND DMGAlbionMarshall, IAPOWER LINES DOWN.
22:30 UTCTSTM WND DMGAlbionMarshall, IATREES DOWN AND UPROOTED.
22:30 UTCTSTM WND DMGLiscombMarshall, IATWELVE INCH DIAMETER LIMB ON CAR.
22:30 UTCTSTM WND DMGMarshalltownMarshall, IAHALF OF TOWN WITHOUT POWER. TREES AND LIMBS UP TO TWELVE INCHES DOWN.
22:30 UTCTSTM WND DMGMarshalltownMarshall, IATREES DOWN AND UPROOTED.
22:30 UTCTSTM WND DMGS MarshalltownMarshall, IATWELVE TO EIGHTEEN INCH TREES SNAPPED OFF.
22:30 UTCTSTM WND GST 63MarshalltownMarshall, IA
22:37 UTCTSTM WND GST 70DikeGrundy, IA
22:39 UTCHAIL 1MaxwellStory, IA
22:40 UTCTSTM WND DMGAlbionMarshall, IAROOF OFF BUILDING. LARGE TREES DOWN.
22:40 UTCTSTM WND GST 70Cedar FallsBlack Hawk, IA
22:43 UTCTSTM WND DMG4 E RandallHamilton, IAMACHINE SHED DESTROYED.
23:00 UTCTSTM WND DMG10 Nne GrinnellTama, IASEVERAL 8-10 INCH TREE BRANCHES DOWN AND CORN BLOWN OVER.
23:02 UTCTSTM WND GST 6010 S WaterlooBlack Hawk, IA

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the trackEvery 2004 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

The other tornadoes of August 3, 2004

3 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
August 34:53 PM CDTF0Hardin, IA0.750$20,000
August 35:00 PM CDTF1Story, IA3.0100$70,000
August 36:13 PM EDTF0Fulton, NY0.110$30,000

What this means

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

Sources

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.