F0 tornado, Farnhamville, Iowa, May 30, 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

May 30, 1998

Touchdown

12:40 PM CDT (17:40 UTC)

Path length

0.1 miles (0.2 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

County

Calhoun County

Touchdown point

42.280, -94.400

Lift-off point

42.280, -94.400

Record number

974

A very unstable airmass was over Iowa. In spite of the instability, the atmosphere was capped by very warm air aloft. Temperatures at the 700 mb level were between 12 degrees C and 14 degrees C. As a result, thunderstorms had a difficult time forming. The atmosphere was primed with CAPE values in the 4000 to 6000 J/kg range by late morning. Helicity values were near 300 M2/S2. One cell was able to break the cap and became severe. It was a prolific hail producer as well as spawning several tornadoes. Hail reports indicated frequent baseball size hail with a few reports to softball size and larger. The largest report was an incredible 5 inch diameter stone north of Gilbert in Story County. The damage caused was incredible. In some town, every north facing window was broken out by the hail. On one building, the hail was so large that it broke the stone tile roof in the building, smashing it into pieces. Property damage was extensive in a swath from Sac County through Marshall County. Total property damage was estimated to be well in excess of $5,000,000. In Calhoun County, the town of Lohrville was hard hit by baseball size hail. Damage in the town was estimated at $1 million as the hail knocked out windows in almost all of the 225 buildings in town. One injury was reported in Lohrville as a woman was treated for an eye injury as shards of glass flew into her eye from a car windshield broken by the hail. Crop damage was difficult to assess, but was extensive. Thousands of acres of crops were shredded by the hail. In Webster County, estimates of crop damage indicated 24,000+ acres had total crop loss and 20,000+ acres suffered 30-50% loss. Crop loss in the county was expected to be over $14 million. In addition to the crop loss, property loss was estimated at between $2 and $4 million. Many emergency managers described the hail event as the worst in 25 years in some areas to the worst they have ever seen in others. To give some idea of the severity, the hail was large enough to shatter tile roofs. Scenes of broken tiles falling off of houses were common. The hail also took a toll on wildlife. Numerous Pheasants, rabbits, and other small animals were killed by the hail, not to mention the smashed birds eggs. The thunderstorm cell itself was a classic cell on WSR-88D radar. It contained a clear hook echo and bounded weak echo region. In spite of the structure looking text book perfect, the cell had a hard time producing a tornado. Several brief touchdowns were reported from northwest of Boone to the vicinity of Boone. The cell became better organized as it moved into central Iowa. A tornado touched down in Story County and moved into Marshall County. This tornado was fairly small and had a very intermittent track. Storm chasers indicated that the tornado lifted several times during its life. Damage was limited as the tornado tracked totally across open country and caused only crop damage for the most part.

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. The outlook in force was issued at 10:20 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.

Fort Dodge (FOD), 34 km from the path, in the two hours either side.

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

The live radar over the trackEvery 1998 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

17 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.