F0 tornado, Tama, Iowa, July 17, 2006

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

July 17, 2006

Touchdown

4:50 PM CDT (21:50 UTC)

Path length

0.2 miles (0.3 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

Property damage

$1,000

County

Tama County

Touchdown point

41.970, -92.620

Lift-off point

41.970, -92.620

Record number

741

A very unstable airmass was in place over Iowa during the afternoon of the 17th, though it was also quite capped. The 700 mb temperature was in the 14 to 15 C. range, making it difficult for thunderstorm activity to initiate. Plenty of moisture was available with CAPE values in the 6000 to 8000 J/kg range based on the surface, and near 5000 J/kg in the mixed layer. Lifted indices fell to near -14 C. by the late afternoon as well. With the exception of the surface, the lower levels were fairly dry. The LCL was in excess of 2100 meters by late afternoon. There was plenty of potential for hail with -10 to -30 C layer CAPE in excess of 1000 J/kg, though the freezing level was in excess of 15,500 feet. Low level lapse rates were in the 8 to 9 C. range in the zero to 3 km layer. The shear environment was fairly favorable by late afternoon with 30 to 40 kts of effective shear. A cold front moved southeast across the state during the afternoon. Ahead of it, a hot and very moist airmass was in place. Afternoon highs were in the mid 90s to around 100 with dew points in the mid to upper 70s. Thunderstorms were not able to fire until the late afternoon hours and only over the far eastern part of the CWA. Once the storms did form, the mode of severe weather was hail. Hail of golf ball, upwards of 3 inch diameter fell in Black Hawk County at Waterloo. The hail path began near the airport and then tracked southeast through downtown Waterloo, causing extensive damage. Tama, Wapello, and Davis Counties were also hit with large hail. Hail of nearly baseball size pelted the countryside south of Bloomfield. One brief tornado touched down in Tama County near Tama. It touched down in an open area just west of town and caused little damage. During the afternoon hours, temperatures in Des Moines reached 100 degrees for the first time since August of 2003. An 83 year old woman was overcome by heat and found dead in her back yard around 1530 in the afternoon.

Tornado touched down briefly in an open area.

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.

The county was under a severe thunderstorm watch, issued at 19:28 UTC and running to 02:00 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, with a 0.02 chance of a tornado within 25 miles. The outlook in force was issued at 20:00 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.

Marshalltown (MIW), 29 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), 95 km away, was scanning. The volume nearest the touchdown began at 21:52 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.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2006 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

2 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.