F2 tornado, Dunkerton, Iowa, May 11, 2000

1. F040 to 72 mph

   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 mphthis tornado

   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

F2

Date

May 11, 2000

Touchdown

7:55 PM CDT (00:55 UTC)

Path length

3.6 miles (5.8 km)

Path width

120 yards (110 m)

Deaths

0

Injuries

0

Property damage

$350,000

County

Black Hawk County

Touchdown point

42.570, -92.230

Lift-off point

42.600, -92.170

Record number

765

The seasons first tornado outbreak took place during the late afternoon and early evening hours of the 11th. During the day, very strong warm air advection took place. Temperatures warmed rapidly during the day with highs reaching the mid to upper 90s over about the southwest half of the state. Dew point temperatures were in the upper 60s to low 70s. This combination produced CAPE values in excess of 8000 J/kg. During the afternoon, a strong cap was in place with 700 mb temperatures around +16 C. This prevented convection from firing during the afternoon. Toward evening, thunderstorms broke through the cap over northeast Iowa. The storms went from initial echo to tornadic storms in less than 50 minutes. A supercell formed west of the Waterloo area. This cell became a splitting cell and produced a brief tornado in Grundy County as the right moving cell split off, and golf ball size hail in Bremer County from the left moving cell. The cell moved off quickly, however additional supercells back developed over the same area. the strongest tornado developed in the Cedar Falls area and tracked across the northern portions of Waterloo. This cell produced a strong tornado which was actually a multi-vortex tornado based on reports from storm chasers in the area. At one point, west of Dunkerton, three tornadoes each one quarter mile wide were on the ground with this storm. The tornado damaged several houses and a few farmsteads along the way. Reports indicated between 5 and 10 houses in Black Hawk County were totally destroyed, and another 15 to 20 sustained significant damage. A total of at least 41 structures sustained at least some damage. In addition to the tornado, damage also occurred south of the track as RFD winds estimated as high as 100 MPH were observed. Dunkerton was hard hit as the tornado moved through. Heavy damage was reported at a coop elevator in Dunkerton, with 10 of 16 grain elevators damaged. A roof was removed from a church as well, resulting in about $500,000 damage. The City Hall building was destroyed in Dunkerton. The City Hall was housed in a series of double wide trailers since ironically the former City Hall building was destroyed just last year in the floods of '99. As the tornado moved through the fairly densely populated area, numerous injuries were reported. Some of the injuries were severe with limbs being cut off by flying debris. One woman lost both one arm and one hand, and had her back broken. She passed away 17 days after her injuries occurred. Six of the injuries occurred at a nursing home that was hit by the tornado. They occurred as the 139 residents were being evacuated. Reports indicated the width of the tornado was up to three-quarters of a mile at its widest. The damage path from the storm was around one and one half miles wide. The tornado continued moving east and crossed into Buchanan County, about 4 miles northeast of Dunkerton. A short time later, another cell developed in the Dunkerton area and dropped a tornado. That tornado struck a farm northwest of town, destroying the farm house and seven outbuildings. In addition to the damage that occurred to the structures, the family dog and one of the five horses on the farm were killed. Reports indicate a letter from one of the farm houses destroyed was found 60 miles away from Dunkerton in the town of Monona in Clayton County. Polly Mill's rural Dunkerton farmhouse was shredded by the tornado. She lost some of her late husband's military medals, pages out of the family Bible, and part of her collection of letters and first-issue stamps. Sixty miles away, on a farm east of Monona, the letter was found in an envelope carrying a first-day issue, 5-cent stamp commemorating the Battle of New Orleans. There was yet a third round of tornadic storms in the Dunkerton area. The last tornado touched down near Dunkerton and developed southward. Two houses in the town of Dunkerton were destroyed by this tornado. In addition to the tornadoes, very heavy rain fell in a narrow area of Black Hawk County. Reports of 3 inches or more of rain was received from the area. Soil conditions were very dry at the time. The dry soil conditions helped preclude any significant flooding. By the afternoon of the 12th, Iowa Governor Vilsack had declared Black Hawk County a state disaster area.

Farm and several outbuildings destroyed

Two houses destroyed

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

11 minutes of warning. NWS DMX issued a tornado warning for this county at 00:44 UTC, 11 minutes before the tornado touched down, in force until 01:15 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 Storm Prediction Center had this point in a Slight Risk. The outlook in force was issued at 20:02 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.

Waterloo (ALO), 17 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Des Moines radar (KDMX), 157 km away, was scanning. The volume nearest the touchdown began at 00:55 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 2000 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

11 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.