EF3 tornado, Mapleton to Mapleton Muni Arpt, Iowa, April 9, 2011

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 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 mphthis tornado

   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

EF3

Date

April 9, 2011

Touchdown

7:20 PM CDT (00:20 UTC)

Lifted

7:26 PM CDT (00:26 UTC)

On the ground

6 minutes

Path length

3.4 miles (5.4 km)

Path width

1,200 yards (1097 m)

Deaths

0

Injuries

14

County

Monona County

Touchdown point

42.154, -95.828

Lift-off point

42.184, -95.777

Record number

1104091820-01

70 damage points were recorded along this path by NWS OAX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF3. The highest wind the damage implies is 155 mph.

• .Also corn stubble in trees
• .trees snappes, corn stubble pulled up
• .numerous tress branvches gone. big tree uprooted.
• .Building collapsed.beams blown over to next block.. photos taken.

Survey points are preliminary and are the raw material the published rating was built from. Source: NWS Damage Assessment Toolkit.

A large upper level trough of low pressure moved from the Rockies east toward the central U.S. on Saturday April 9th. As it did, it caused a warm front to lift into eastern Nebraska and western Iowa. Temperatures south of the front were in the 80s with dew point temperatures in the 60s. Meanwhile, readings north of the boundary were in the 50s and 60s. Moderate instability south of the front combined with high levels of wind shear allowed for supercell development over eastern Nebraska and southwest Iowa during the late afternoon and early evening of April 9th. A few of the storms that were near the front turned tornadic while the other supercells were prolific hail producers, in some cases producing very large hail.

A tornado caused extensive damage in the Mapleton area with about 100 houses destroyed and many others severely damaged in a 12 to 15 block area on the southwest side of town. This caused the displacement of around 500 to 600 people. Most garages and stand alone structures were destroyed. In addition, large trees were uprooted and windows blown out of vehicles. Twelve to 14 people sustained minor injuries, the most severe a broken leg. The worst property damage was noted to be on the lower end of the EF3 category. The tornado started about 2 miles west southwest of Mapleton, moved into town, then turned north and ended 1 mile north of town. The path length was around 3.5 miles and the maximum width was around 3/4 of a mile.

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

12 minutes of warning. NWS OAX issued a tornado warning for this county at 00:08 UTC, 12 minutes before the tornado touched down, in force until 00:41 UTC.

The county was under a tornado watch, issued at 22:49 UTC and running to 03:52 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, with a 0.10 chance of a tornado within 25 miles. The outlook in force was issued at 20:01 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.

Denison (DNS), 40 km from the path, in the two hours either side.

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

The Omaha radar (KOAX), 105 km away, was scanning. The volume nearest the touchdown began at 00:21 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 2011 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

27 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.