F1 tornado, Hopkinton, Iowa, August 26, 2004

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 mphthis tornado

   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

F1

Date

August 26, 2004

Touchdown

10:51 PM CDT (03:51 UTC)

Path length

4.2 miles (6.8 km)

Path width

440 yards (402 m)

Deaths

0

Injuries

0

Property damage

$70,000

County

Delaware County

Touchdown point

42.350, -91.250

Lift-off point

42.380, -91.220

Record number

467

Tornado developed just south of Hopkinton and moved northeast for 0.15 miles to the edge of Hopkinton. Tornado then turned right and moved roughly east northeast for 1 mile destroying 2 machine sheds and damaging a third while toppling many trees on the Wendt Farm. At this point, the tornado began an arcing turn to the left for the remainder of its life. It crossed 300th Avenue one quarter of a mile south of 305th Street and went through the Lamont Farm. An old barn was moved off its foundation for approximately 50 yards. The tornado crossed 305th Street about one half mile east of 300th Avenue and moved northeast through the Feldman Farm. Here several large trees were damaged or destroyed with damage to several metal machine sheds. A grain bin was destroyed and scattered across the field. The tornado crossed 300th Street 0.2 miles west of County X47 and crossed X47 about one half mile north of 300th Street. The tornado dissipated just to the east of X47 and just south of 295th Street. The width of the path varied from as narrow as 10 yards to one quarter mile wide.

Rated high F1

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. One was issued for the county at another hour that day.

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 Moderate Risk, with a 0.15 chance of a tornado within 25 miles. The outlook in force was issued at 20:18 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.

Monticello Municipal (MXO), 17 km from the path, in the two hours either side.

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

The Quad Cities radar (KDVN), 100 km away, was scanning. The volume nearest the touchdown began at 03:50 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

14 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.