F1 tornado, Farnhamville to Slifer, Iowa, May 18, 2005

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

May 18, 2005

Touchdown

6:58 PM CDT (23:58 UTC)

Path length

24.5 miles (39.4 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$90,000

Counties

Calhoun and Webster counties

Touchdown point

42.319, -94.424

Lift-off point

42.422, -94.111

Record number

737

The frontal boundary from Nebraska moved into western Iowa during the evening hours. The airmass was unstable, but not overly so. CAPE values were around 1500 J/kg with Lifted Indices around -2. There was about 45 kts of effective shear in place. A few thunderstorms developed ahead of the boundary with one of the cells becoming severe. The first tornado occurred in Calhoun County at 2358 UTC where the tornado dropped into a farm field between York ave and Zearing Ave south of 320th St. about 2 miles north of Farnhamville. The tornado was an F1 tornado as it crossed the intersection of Zearing and 320th St. IT destroyed dome outbuildings north of the intersection and continued moving northeast toward Slifer in Webster County. The tornado remained on the ground crossing the Calhoun/Webster County line crossing County Road D46 between Zebulon Ave and County Road P29. The tornado destroyed three grain bins and just missed a farm. Debris was tossed over several hundred yards before the tornado weakened and lifted for the first time prior to reaching Slifer. The F1 tornado was on the ground for about 4 miles during this time with F1 strength and a width of 50 to 100 yards. The tornado was reported on the ground very intermittently from this point on with numerous reports southwest of Callender, northeast through the Woodman Hol State preserve and into the Brushy Creek State Reserve. At this point, the tornado lifted. The parent storm continued into Hamilton County. A brief touchdown was reported in Hamilton County north of Blairsburg. No damage was reported and the tornado roped out quickly.

Tornado touched down on a farm north of Farnhamville, damaging several buildings on the farm. The tornado moved from Calhoun County into Webster County.

Tornado moved from Calhoun County into Webster County. It moved through mostly open country and have a very intermittent track from Slifer on northeast. Damage occurred to several grain bins, then tornado lifted for some time with another tornado forming over Hamilton County.

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, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 19:45 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), 21 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 2005 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

6 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.