F0 tornado, Dedham, Iowa, April 17, 2002

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

April 17, 2002

Touchdown

10:40 PM CDT (03:40 UTC)

Path length

0.5 miles (0.8 km)

Path width

40 yards (37 m)

Deaths

0

Injuries

0

Property damage

$1,000

County

Carroll County

Touchdown point

41.900, -94.680

Lift-off point

41.900, -94.680

Record number

499

The cold front mentioned in the previous event washed out and stalled south of Iowa. An east to west boundary set up along the Iowa Missouri border. There was little in the way of temperature contrast across the boundary, however there was a very significant dew point discontinuity. Dew point readings were in the mid 30s to low 40s north of the boundary, while they were in the mid 60s to the south of it. During the evening hours, a low level get formed with winds of 50 to 65 kts blowing across the boundary. A supercell formed over eastern Nebraska and moved east-northeast into Iowa. There were a few other cells that formed during the evening, however most of the severe weather was associated with the one supercell. Hail from three quarters of an inch to two inches in diameter was common with the storm as it moved through. The supercell produced two tornadoes. Both of them were only on the ground briefly and caused little damage. The first was in Carroll County east of Dedham. The second was in Boone County west of Madrid. Later in the evening, a cluster of thunderstorms formed to the northwest of the supercell. In Kossuth County, hail nearly an inch in diameter nearly covered the ground along a two to three mile path near Fenton.

Brief touchdown with only minor damage.

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

1 minute of warning. NWS DMX issued a tornado warning for this county at 03:39 UTC, 1 minute before the tornado touched down, in force until 04:15 UTC.

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 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 live radar over the trackEvery 2002 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

5 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.