EF2 tornado, Rock Vly to Inwood, Iowa, May 1, 2008

1. EF065 to 85 mph

   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 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. 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

EF2

Date

May 1, 2008

Touchdown

6:59 PM CDT (23:59 UTC)

Lifted

7:24 PM CDT (00:24 UTC)

On the ground

25 minutes

Path length

12.9 miles (20.8 km)

Path width

400 yards (366 m)

Deaths

0

Injuries

0

Property damage

$510,000

Counties

Sioux and Lyon counties

Touchdown point

43.142, -96.300

Lift-off point

43.295, -96.416

Record number

0805011759-01

Thunderstorms produced 5 confirmed tornadoes over extreme northwest Iowa during the early evening hours of May 1st. One large long track tornado caused considerable damage, while the other 4 tornadoes were short lived and weak.

A tornado damaged numerous trees, including large trees uprooted, blew windows out of a home, destroyed a metal shed, blew two windows and part of a wall out of a metal building, damaged at least three grain bins, destroyed or damaged numerous outbuildings and small sheds, blew down or snapped off at least 15 power poles, bent a metal light pole, tipped one wagon and blew the top off another, blew down a barb wire fence and pushed fence posts almost to the ground, destroyed a hog barn, and flattened corn stubble, before crossing the county line into Lyon County. Contents inside several damaged or destroyed buildings and sheds were also damaged, especially on one farm where damaged buildings housed a farm and trucking business.

A tornado that crossed from Sioux County damaged a barbed wire fence, damaged or destroyed at least three outbuildings, caused minor damage to a home, and blew out or flattened corn stubble.

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

5 minutes of warning. NWS FSD issued a tornado warning for this county at 23:54 UTC, 5 minutes before the tornado touched down, in force until 00:30 UTC.

The county was under a tornado watch, issued at 21:34 UTC and running to 02:19 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 19:59 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.

Orange City (ORC), 35 km from the path, in the two hours either side.

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

The Sioux Falls radar (KFSD), 51 km away, was scanning. The volume nearest the touchdown began at 23:55 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 2008 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

21 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.