F0 tornado, Dayton, Iowa, April 6, 1998

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 6, 1998

Touchdown

6:55 PM CDT (23:55 UTC)

Path length

0.1 miles (0.2 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

County

Webster County

Touchdown point

42.250, -94.070

Lift-off point

42.250, -94.070

Record number

902

A southeast flow of moist air was in place over Iowa. This flow brought moisture north with surface dew point temperatures rising into the low to mid 50s. Lapse rates were steep with the freezing level only around 9000 feet. The low freezing level contributed to widespread hail as thunderstorms formed during the mid afternoon hours. Synoptically, an upper level low pressure system was advancing northeast from the southwest U.S. A surface low formed over Oklahoma with a trough extending northeast into eastern Nebraska. This trough served as the focusing boundary for the thunderstorms to form on. Initially , a small cluster of thunderstorms formed over southeast Nebraska and moved into southwest and west central Iowa. Most of the storms produced at least pea to marble size hail. There were several reports of hail covering the ground. In Carroll County, pea to slightly larger size hail accumulated to a depth of an inch in the town of Arcadia. Significant hail fell in Boone and Webster Counties where golf ball size hail was reported. The area around Dayton was particularly hard hit with the golf ball size hail covering the ground. During the storms strongest period, several small tornadoes were spawned. One touched down briefly in Greene County north of Churdan. A short time later, two other brief touchdowns were reported. A Ham radio spotter reported a brief touch down near Highway 169 in Webster County south of Dayton. Another brief touchdown occurred in Green County north of Scranton near the same time. All of these tornadoes touched down in open fields and caused little to no damage. They were also quite small and weak. The other problem during this event was with the rainfall. The soil in Iowa was already close to saturation. As a result, much of the rain that fell ran off, causing local and urban flooding. Rainfall of one to three inches was common from west central Iowa into parts of the north central counties. The heaviest rainfall report was received from Denison with 3.40 inches. There were several reports of one to two inches falling in one half hours time. In spite of the wet soil conditions and heavy rainfall, flooding was relatively minor, though considerable ponding did occur.

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

31 minutes of warning. NWS DMX issued a tornado warning for this county at 23:24 UTC, 31 minutes before the tornado touched down, in force until 23:55 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 19:29 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.

Webster City (EBS), 27 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), 64 km away, was scanning. The volume nearest the touchdown began at 23:54 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 1998 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

5 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.