F0 tornado, Sheffield, Iowa, September 2, 2006

1. F040 to 72 mphthis tornado

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

2. F173 to 112 mph

   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.

Rating

F0

Date

September 2, 2006

Touchdown

3:37 PM CDT (20:37 UTC)

Path length

0.2 miles (0.3 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

County

Franklin County

Touchdown point

42.900, -93.330

Lift-off point

42.900, -93.330

Record number

862

A cold front advanced into Iowa in advance of a strong upper air low pressure that was over central South Dakota. Instability was marginal with CAPE values in the 1000 J/kg range and lifted indices in the -2 to -4 C. range. A weak shear environment was in place with 20 kts or less of shear in the 0-6 km layer. Much of the CAPE that was available was in the lowest levels of the atmosphere. Thunderstorms erupted along the initial surface boundary during peak heating. With LCL in the 600-1000 meter range, combined with the amount of low level CAPE, the thunderstorms produced numerous funnel clouds. There were three reported touchdowns. They were actually more of a landspout that a full fledged tornado. Little damage occurred as they touched down briefly in open farm files. The thunderstorms also produced some localized very heavy rainfall. Satellite pictures shows evidence of a strong tropical connection to Hurricane John in the east Pacific. Local rainfall of 3 to 4.5 inches in about an hour was reported on the west side of the Des Moines metropolitan area. There were several reports of 1 to 3 inch rainfall along the Interstate 35 corridor. Some local street flooding was reported through this area.

Brief tornado touchdown in open fields.

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. One was issued for the county at another hour that day.

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 General Thunderstorms Risk, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 19:52 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), 134 km away, was scanning. The volume nearest the touchdown began at 20:36 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 2006 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

2 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.