F0 tornado, Runnells, Iowa, April 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

April 2, 2006

Touchdown

5:31 PM CDT (22:31 UTC)

Path length

0.2 miles (0.3 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

County

Polk County

Touchdown point

41.550, -93.370

Lift-off point

41.550, -93.370

Record number

231

An early spring storm lifted northeast out of the southwest U.S. The surface low pressure moved northeast into Iowa during the afternoon and pushed northeast out of the state during the evening. The dry punch moved into southern Iowa during the afternoon and the airmass became unstable. Lifted indices fell to the -1 to -4 C. range with CAPE values in the 400 to 1000 J/kg range. The LCL was fairly low during the afternoon, in the 600 to 800 meter range. With the upper low pressure area also lifting northeast into Iowa, the freezing level was quite low at 9700 feet AGL. Thunderstorms formed in an arc across Iowa at the nose of the dry punch. The storms lifted north into the central sections of the state by late afternoon. Many of the storms produced hail, some of which was severe. Reports of large hail were absent however. There were several reports of brief tornado touchdowns. None of them remained on the ground for more than a couple of minutes. Two brief touchdowns occurred in Davis County early on in the event. During the late afternoon, as the line of storms approached central Iowa, several brief touchdowns occurred. These reports were to the south of Des Moines in Warren County, and to the east of Des Moines in southeast Polk County. Damage report were limited as the touchdowns were so brief. As the storms moved across Warren County, high winds blew a car off the road near Carlisle. No injuries were reported.

Brief tornado touchdown in open fields.

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

20 minutes of warning. NWS DMX issued a tornado warning for this county at 22:11 UTC, 20 minutes before the tornado touched down, in force until 22:45 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 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 19:55 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), 36 km away, was scanning. The volume nearest the touchdown began at 22:29 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

66 more were confirmed in the United States that day.

All 67 of them

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.