F2 tornado, Scarville to Joice, Iowa, August 9, 1999

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 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. F2113 to 157 mphthis tornado

   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

F2

Date

August 9, 1999

Touchdown

9:02 PM CDT (02:02 UTC)

Path length

11.5 miles (18.5 km)

Path width

40 yards (37 m)

Deaths

0

Injuries

0

Property damage

$150,000

Counties

Winnebago and Worth counties

Touchdown point

43.470, -93.620

Lift-off point

43.400, -93.520

Record number

1326

An unstable airmass was in place over Iowa during the afternoon and evening hours of the 9th. Satellite and sounding data suggested the atmosphere was capped at about 775 mb by a warm layer of air with temperatures as high as 18 C. or more. Thunderstorms had a hard time firing off. A cold front moved southeast into the state as rich low level air with dew point temperatures in the mid 70s preceded the front. While the front moved southeast, a speed max near 100 kts in strength moved into the north central U.S. This combined with an upper level short wave helped a few of the storms break the cap. The wind profile was favourable with a strong shearing environment. Thunderstorms moved into north central Iowa and became tornadic quickly. There was basically one cell that produced at least two tornadoes as it slipped southeast into Iowa. The first tornado touched down in Winnebago County near Scarville. The tornado moved southeast across the county and advanced into Worth County by a few miles. The tornado caused crop damage and some building damage along its path. The corner of a bank building was torn off in the town of Joice in Worth County for example. The same cell produced another brief tornado touchdown near Burchinal in Cerro Gordo County near the intersection of I-35 and County Highway B-43. No significant damage was reported with this tornado. As the large cell that produced the tornado moved on, the rear flank downdraft produced high winds once again in the Scarville area. Power lines were downed and a few buildings were damaged by the high winds in the town of Scarville. High winds also struck the airport in Mason City with a wind gust of 58 MPH.

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

2 minutes of warning. NWS DMX issued a tornado warning for this county at 02:00 UTC, 2 minutes before the tornado touched down, in force until 02:35 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 Moderate Risk. The outlook in force was issued at 00:38 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.

Albert Lea (AEL), 32 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 1999 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

11 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.