EF0 tornado, Holmes, Iowa, June 21, 2007

1. EF065 to 85 mphthis tornado

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

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

3. EF2111 to 135 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. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 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

EF0

Date

June 21, 2007

Touchdown

3:55 PM CDT (20:55 UTC)

Path length

0.1 miles (0.2 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

Crop damage

$2,000

County

Wright County

Touchdown point

42.700, -93.800

Lift-off point

42.700, -93.800

Record number

0706211455-01

A warm, moist, and unstable airmass was in place over Iowa on the afternoon of the 21st. A Warm front lifted north into the state with temperatures rising into the upper 80s to low 90s south of it with dew point temperatures in the upper 60s to low 70s. This combination produced most unstable CAPE values in the 3000 to 4000 J/kg range and lifted indices in the -9 C. range. The environment was not strongly sheared with 25 to 35 kts of effective shear. The freezing level was quite high at 14,700 feet. In spite of this, there was plenty of cape in the -10 to -30 C. layer of the atmosphere, with 500 J/kg available. The LFC in the 1200 to 2000 meter range. The MCS developed rapidly and move east-southeast across Iowa. Many of the storms produced significant hail, with hail size ranging from nickel to over tennis ball size. Two and one half inch diameter hail fell north of Renwick in Humboldt County. Golf ball size hail fell in Hancock County in the Corwith area. The largest hail occurred during the first couple hours of the systems development. Most of the hail was in the three quarter to one inch diameter range later on. Four tornadoes were reported with the system. All of the were brief touchdowns however and caused little damage. One touched down in Wright County near Eagle Grove. Two others touched down in Butler County one west of Shell Rock, the other north of Steamboat Rock. The fourth tornado touched down northwest of Kelly in Story County. The final tornado touched down on the south side of Waterloo in Black Hawk County. Many of the storms produced strong winds of at least 45 to 50 MPH. There were several reports of winds in excess of 60 MPH however. Numerous trees were blown down and a few power poles snapped. Winds caused damage in the Poweshiek County with winds estemated at near 80 MPH.

Report of a brief tornado touchdown. No significant damage.

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

16 minutes of warning. NWS DMX issued a tornado warning for this county at 20:39 UTC, 16 minutes before the tornado touched down, in force until 21:15 UTC.

The county was under a severe thunderstorm watch, issued at 17:00 UTC and running to 23:47 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 19:46 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.

Clarion (CAV), 6 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), 108 km away, was scanning. The volume nearest the touchdown began at 20:55 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 2007 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

7 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.