Tornadoes · United States · Iowa · 2005

F1 tornado, Story County, Iowa, September 8, 2005

This F1 tornado ran 0.7 miles across Story County on September 8, 2005, touching down at 12:30 PM CDT and reaching 75 yards wide. It killed nobody and injured 8, and did $150,000 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
September 8, 2005
Touchdown
12:30 PM CDT (17:30 UTC)
Path length
0.7 miles (1.1 km)
Path width
75 yards (69 m)
Deaths
0
Injuries
8
Property damage
$150,000
County
Story County
Touchdown point
42.030, -93.620
Lift-off point
42.030, -93.620
Record number
376

The warnings

No tornado warning for this county appears in the archive as in force at the moment the tornado touched down.

Issued (UTC)ExpiredProductOffice
16:55 UTC17:45 UTCSevere Thunderstorm WarningDMX
17:33 UTC18:23 UTCSevere Thunderstorm 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 Slight Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 16:20 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.

Omaha, NE (KOAX), 12:00Z

5.5 hours before the tornado, 242 km from the path. September 8, 2005.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 12:00Z on 2005-09-08Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 150 joules per kilogram, CIN -186, lifted condensation level 1545 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, Omaha, NE at 12:00Z on 2005-09-08The 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 113 square meters per square second, 0 to 6 km bulk shear 38 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
150 J/kg
Mixed-layer CIN
-186 J/kg
Surface CAPE
193 J/kg
Mixed-layer LCL
1545 m above ground
0-6 km bulk shear
38 kt
0-1 km bulk shear
21 kt
0-1 km storm-relative helicity
113 m²/s²
0-3 km storm-relative helicity
135 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.2
0-3 km lapse rate
4.7 K/km

Open this sounding in Storm Lab

Omaha, NE (KOAX), 00:00Z

6.5 hours after it, 242 km from the path. September 9, 2005.

Skew-T log-pSkew-T log-p diagram, Omaha, NE at 00:00Z on 2005-09-09Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 1343 joules per kilogram, CIN -87, lifted condensation level 1948 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, Omaha, NE at 00:00Z on 2005-09-09The 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 -10 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
1343 J/kg
Mixed-layer CIN
-87 J/kg
Surface CAPE
2626 J/kg
Mixed-layer LCL
1948 m above ground
0-6 km bulk shear
31 kt
0-1 km bulk shear
5 kt
0-1 km storm-relative helicity
-10 m²/s²
0-3 km storm-relative helicity
-2 m²/s²
Significant tornado parameter
0.0
Supercell composite
1.2
0-3 km lapse rate
7.1 K/km

Open this sounding in Storm Lab

The surface observations

Ames (AMW), 4 km from the path, in the two hours either side.

Time (UTC)Temp (°F)Dew point (°F)WindGust (kt)Pressure (mb)Weather
15:53 UTC7466150° 8 kt1019.3VCTS
16:53 UTC7367160° 6 kt1018.3VCTS HZ
17:53 UTC626210° 17 kt321020.3+TSRA FG
18:53 UTC646170° 7 kt1017.9

From the Iowa Environmental Mesonet's archive of airport observations.

The radar

The Des Moines radar (KDMX), 34 km away, was scanning. The volume nearest the touchdown began at 17:30 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
16:50 UTCTSTM WND DMGPatonGreene, IATREE DOWN ON HOUSE. MANY 20 INCH DIAMETER LIMBS DOWN IN TOWN.
17:20 UTCTSTM WND DMG1 Ese BooneBoone, IANUMEROUS LARGE TREES AND LIMBS DOWN.
17:30 UTCTSTM WND DMGAmesStory, IATWO FOOT DIAMETER TREE DOWNED. LARGE TENT BLOWN DOWN. REPORTED BY PUBLIC.
17:30 UTCTSTM WND DMGMadridBoone, IA6-12 INCH TREE LIMBS DOWN. SMALL METAL BUILDINGS DOWN.
17:30 UTCTSTM WND GST 62MadridBoone, IAFROM KCCI SCHOOL NET
17:30 UTCTORNADOAmesStory, IANEAR POWER PLANT ON ISU CAMPUS.
17:35 UTCTSTM WND DMGMadridBoone, IANUMEROUS LARGE TREE LIMBS DOWN AND STREET SIGNS SNAPPED. REPORTED BY BOONE COUNTY SHERIFFS DEPARTMENT.
17:35 UTCTSTM WND GST 70Pleasant HillPolk, IAON HIGHWAY 163...SOUTH OF ALTOONA.
17:35 UTCTSTM WND GST 83AmesStory, IAON THE ISU CAMPUS - AGRONOMY BUILDING.
17:36 UTCTSTM WND GST 81AmesStory, IA
17:36 UTCHAIL 0.88Des MoinesPolk, IANEAR 38TH AND DOUGLAS INTERSECTION.
17:45 UTCTSTM WND DMG2 Sw MadridDallas, IANUMEROUS LARGE TREES DOWN. REPORTED BY TRAINED SPOTTER.
17:45 UTCTSTM WND GST 601 S SheldahlPolk, IAREPORTED BY AMATEUR RADIO SPOTTER.
17:45 UTCHAIL 11 S SheldahlPolk, IAQUARTER SIZE HAIL REPORTED BY AMATEUR RADIO SPOTTER.
17:50 UTCTSTM WND GST 602 Sw AnkenyPolk, IAREPORTED BY AMATEUR RADIO SPOTTER.
17:51 UTCTSTM WND GST 834 E AnkenyPolk, IARAINFALL 0.81
17:55 UTCTSTM WND DMG5 Nw Ankeny Regional AiPolk, IATREE DAMAGE...POWER OUTAGES NEAR/ALONG ANKENY BLVD...DELAYED REPORT
17:55 UTCTSTM WND GST 75AnkenyPolk, IADELAYED REPORT
17:57 UTCTSTM WND DMGAltoonaPolk, IASEMI TRAILER AND CAMPER OVERTURNED ON INTERSTATE 80 JUST WEST OF EXIT 141. REPORTED BY AMATEUR RADIO SPOTTER.
17:57 UTCHAIL 0.885 Nw Des MoinesPolk, IA55 MPH WIND GUST...DELAYED
18:00 UTCHAIL 1.752 W ElkhartPolk, IAAT THE ELKHART EXIT OF I35.
18:07 UTCHAIL 0.88Des MoinesPolk, IANEAR 38TH AND DOUGLAS INTERSECTION.
18:10 UTCTSTM WND DMGColfaxJasper, IATREES AND POWER LINES DOWN.
18:10 UTCTSTM WND DMGMarshalltownMarshall, IATREE AND LARGE LIMBS DOWN BLOCKING STREETS
18:10 UTCTSTM WND GST 703 S AltoonaPolk, IAON HIGHWAY 163...SOUTH OF ALTOONA.
18:10 UTCTSTM WND GST 70Pleasant HillPolk, IAON HIGHWAY 163...SOUTH OF ALTOONA.
18:10 UTCHAIL 1.5Pleasant HillPolk, IAHIGHWAY 163 SOUTH OF ALTOONA
18:15 UTCTSTM WND DMGBaxterJasper, IAPOWERLINES AND POWER POLE BLOWN DOWN.
18:36 UTCTSTM WND DMG5 Nw Ankeny Regional AiPolk, IATREE DAMAGE...POWER OUTAGES NEAR/ALONG ANKENY BLVD...DELAYED REPORT

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

This ground now

The live radar over the trackEvery 2005 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

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.