EF0 tornado, Sewal, Iowa, March 21, 2007

1. EF065 to 85 mphthis tornado

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

2. EF186 to 110 mph

   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

EF0

Date

March 21, 2007

Touchdown

12:39 AM CDT (05:39 UTC)

Lifted

12:41 AM CDT (05:41 UTC)

On the ground

2 minutes

Path length

1.4 miles (2.3 km)

Path width

35 yards (32 m)

Deaths

0

Injuries

0

Property damage

$150,000

County

Wayne County

Touchdown point

40.625, -93.307

Lift-off point

40.630, -93.281

Record number

0703212339-01

During the day, south winds drew moisture north into the state as a warm front lifted north across the area. By evening, low pressure lifted north along a cold front to the west of the state. The cold front advanced into the state during the evening. Convection was limited during the afternoon due to a mid level cap and considerable low level cloudiness. Still, the atmosphere became quite unstable by the evening hours. Surface temperatures rose to the mid 60s to mid 70s across the CWA with dew points rising into the upper 50s to low 60s. Effective shear was in the 30 to 45 kt range with most unstable CAPE values in the 1000 to 2000 J/kg range. Lifted indices fell to the -3 to -6 C. range by evening. As was the case during the morning, freezing levels were in the 11,000 to 12,000 foot range. CAPE in the -10 to -30 C. layer was around 200 J/kg. Thunderstorms developed just ahead of the cold front on the west edge of the mid level cap before sunset. The storms took on a linear configuration as the moved into the state. There were two stronger areas along the line. The first was across the northern part of the state, the second along the southern two tiers of counties. Most of the storms produced hail with most reports around an inch in diameter or less. The southern part of the line took on more of a bow echo appearance and began to produce high winds. Wind gusts to near 60 MPH in Bedford in Taylor County, and in the 50 to 60 MPH range northwest of Lamoni in Decatur County. One tornado touched down in Wayne County. The tornado had an intermittent track, touching down southwest of the town of Sewal and dissipating about a mile northeast of town. Damage was done to buildings on the south side of the town. The tornado was rated an EF0, with winds of 80-85 MPH. The tornado broke apart east of Sewal with a band of downburst winds of up to 80 MPH extending across the county line into Appanoose County.

Tornado touched down southwest of Sewal and caused damage to building on the south side of town. It had an intermittent track, finally lifting about a mile east of town. The tornado was a high end EF0 tornado with winds of 80 to 85 MPH.

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.

The county was under a severe thunderstorm watch, issued at 03:25 UTC and running to 07:14 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 01:11 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), 128 km away, was scanning. The volume nearest the touchdown began at 05:38 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

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.