F0 tornado, Rockwell City, Iowa, June 1, 1999

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

June 1, 1999

Touchdown

4:55 PM CDT (21:55 UTC)

Path length

0.1 miles (0.2 km)

Path width

20 yards (18 m)

Deaths

0

Injuries

0

County

Calhoun County

Touchdown point

42.400, -94.580

Lift-off point

42.400, -94.580

Record number

357

A frontal system stalled to the south of Iowa during the night of the 1st and began to lift north as a warm front during the day on the 2nd. At the same time an upper low moved northeast into the state. A surface low also formed under the upper low and moved along the front. Initial convection kicked off south of the surface low in the warm sector as a dry line punched east under the low. The storms that formed remained below severe levels, but did produce heavy rain and pea to marble size hail. As the upper low advanced east, a comma precipitation pattern formed. The head of the comma was over Butler County as heavy thunderstorms moved into the county and then stopped. As the vorticity maximum moved through the area, the storms began to sag slowly south and weaken. In the process, upwards of 2 to 3.1 inches of rain fell over much of Butler County. This caused urban flooding problems, but not too serious. Water was reported over some roads for a while, but the water receded once the rain tapered off. Meanwhile, over western Iowa, small thunderstorms formed in what would be the deformation zone under the cold pool aloft. The storms were popcorn variety and lasted for 15 minutes or less. A few of the storms produced cold air funnels. One storm in Calhoun County produced a brief spin up tornado. The tornado did not do any damage and would better be described as a landspout rather than a tornado.

Brief spinup landspout

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.

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 General Thunderstorms Risk. The outlook in force was issued at 16:40 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 live radar over the trackEvery 1999 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

30 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.