F0 tornado, Bradford to Ackley, Iowa, August 16, 2004

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

August 16, 2004

Touchdown

7:10 PM CDT (00:10 UTC)

Path length

0.6 miles (1.0 km)

Path width

40 yards (37 m)

Deaths

0

Injuries

0

Property damage

$1,000

Counties

Hardin and Franklin counties

Touchdown point

42.530, -93.120

Lift-off point

42.550, -93.070

Record number

1455

A weak cold front settled southeast into Iowa during the evening hours. The airmass ahead of the front was marginally unstable with lifted indices of -4 to -5 and CAPE values in the 2000 to 3000 J/kg range. Thunderstorms erupted over north central into northeast Iowa initially. Inflow to the thunderstorms was in the 15 to 30 kt range. Farther west, inflow was under 10 KTS, which limited thunderstorm development. Intense thunderstorms formed over Franklin, Butler, and Hardin Counties. One of the storms produced tornadoes over Franklin and Hardin Counties. One tornado touched down in rural Franklin County and crossed the border into Hardin County. A second tornado touched to the west and south of Ackley in Hardin County. This tornado also touched down in rural areas and caused little damage. High winds swept through Ackley as the storms moved through. There were several reports of hail of nickle to ping ball size. The storms trained over Butler and Hardin Counties. Rainfall of 2 to 4 inches in a two to three hour period resulted in flash flooding over southwest Butler, northeast Grundy, and northeast Hardin Counties. Later in the evening thunderstorms formed along the outflow of the convection in northeast Iowa. Thunderstorms fired briefly along the boundary and became severe, producing three quarter to one inch diameter hail.

Tornado touched down in farm fields southeast of Bradford. Tornado then crossed the county line into Hardin County.

Tornado moved from Franklin County into northern Hardin County. It was in open fields.

Tornado touched down in farm fields and remained in open country. It caused little damage.

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

5 minutes of warning. NWS DMX issued a tornado warning for this county at 00:05 UTC, 5 minutes before the tornado touched down, in force until 00:30 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 19:59 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), 104 km away, was scanning. The volume nearest the touchdown began at 00:07 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.

The live radar over the trackEvery 2004 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

3 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.