EF1 tornado, Seymour, Iowa, October 2, 2007

1. EF065 to 85 mph

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

2. EF186 to 110 mphthis tornado

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

3. EF2111 to 135 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. EF3136 to 165 mph

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

5. EF4166 to 200 mph

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

6. EF5over 200 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.

Rating

EF1

Date

October 2, 2007

Touchdown

5:35 PM CDT (22:35 UTC)

Lifted

5:37 PM CDT (22:37 UTC)

On the ground

2 minutes

Path length

0.9 miles (1.5 km)

Path width

20 yards (18 m)

Deaths

0

Injuries

0

Property damage

$100,000

County

Wayne County

Touchdown point

40.678, -93.126

Lift-off point

40.684, -93.110

Record number

0710021635-02

Following the morning convection, there was little break before the cold front mentioned in the previous narrative moved into the state. The cold front advanced across the state accompanied by a strong upper level short wave. Severe parameters were not all that impressive, however it was a case of low top convection close to the upper low. The zero to 1 km helicity was quite high, in the 350 to 400 J/kg range and there was significant shear with effective shear in the 50 to 60 kt range. Other parameters were not all that impressive with most unstable CAPE in the 500 to 1000 J/kg range and lifted indices between zero and -3 C. The downdraft CAPE was around 500 J/kg with only about 100 J/kg of CAPE available in the -10 to -30 C. layer of the atmosphere. The LCL was quite low given the saturation caused from the previous convection. It was between 750 and 1000 meters. As the line of convection from the morning shifted to the east, a narrow line of strong thunderstorms developed along the cold front and the approach of the upper low. Initially, downburst winds occurred with the line with winds estimated around 65 MPH south of New Market in Taylor County. A short distance to the west of the CWA, a 75 MPH wind gust occurred at an RWIS site. As the storms raced east they produced gusty winds and very heavy rainfall. The storms produced a small, but intense, tornado in downtown Des Moines. Two power poles snapped and power lines down at 13th and Mulberry. At 6th and Mulberry, two vehicles were flipped including one SUV that was likely flipped nose down due to engine weight. The SUV slid about 30 feet. Eyewitness saw a small 10 foot tree lifted into the circulation and rotating around briefly. Media reported some roof debris on the SW 9th overpass at Martin Luther King Parkway, but no building damage is evident at this time. Some buildings were damaged in the area. Multi story and roof damage would be difficult To see from the street. The tornado was rated an EF1 with 110 MPH winds. This was the first tornado to touchdown in the Des Moines city limits since 30 May, 2000. High winds hit just east of the Des Moines Airport, blowing out the windows of 6 cars in a parking lot. As the storms moved east, another tornado touched down near the town of Seymour, in Wayne County. A farmer reported seeing a tornado touch down just southwest of Seymour. The tornado tore metal roofing off his shed. The tornado curved through town, blowing open doors at a school but causing little damage to the school. Windows were blown out of a church and a large tree feel to the west, knocking out power. A fabric roof was partially torn off a hoop storage shed at the elevator in town. A few trees were also topped. Path was very narrow and intermittent No other damage in the county. The tornado was rated an EF1 with 95 MPH winds. Two other small tornadoes touched down in Mahaska County. One was east-northeast of Bussy and was on the ground for about 4 minutes. The tornado tracked through open fields and only did agricultural damage. The second was an anti-cyclonic tornado that touched down briefly in an open field southeast of Bussy.

The Wayne County EM reported a roof blown off of a building, windows blown out of homes, and power lines down in the town of Seymour.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

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

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 Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 20:00 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 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.

The Des Moines radar (KDMX), 127 km away, was scanning. The volume nearest the touchdown began at 22:33 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.

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

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

The live radar over the trackEvery 2007 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

14 more were confirmed in the United States that day.

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.

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