EF2 tornado, Arthur to Galva, 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 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

April 9, 2011

Touchdown

8:20 PM CDT (01:20 UTC)

Lifted

8:28 PM CDT (01:28 UTC)

On the ground

8 minutes

Path length

4.1 miles (6.6 km)

Path width

440 yards (402 m)

Deaths

0

Injuries

0

Property damage

$50,000

County

Ida County

Touchdown point

42.322, -95.397

Lift-off point

42.375, -95.361

Record number

1104091920-01

Thunderstorms produced widespread severe weather in northwest Iowa during the evening of April 9th, beginning at the end of the afternoon. Most of the reports at the start of the event were large hail, but damaging winds and tornadoes then developed, with significant damage reported.

A tornado destroyed or heavily damaged two grain bins and two outbuildings on a farmstead. The tornado also caused mainly shingle damage to a house and garage on the same farmstead. Trees, power poles, and power lines were also damaged.

A tornado severely damaged a farmstead; taking the roof off of a house and destroying numerous outbuildings. The tornado also damaged outbuildings at another farmstead, snapped at least 5 power poles, and damaged an outbuilding at an ethanol plant. The tornado also caused tree damage.

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

24 minutes of warning. NWS FSD issued a tornado warning for this county at 00:56 UTC, 24 minutes before the tornado touched down, in force until 01:30 UTC.

The county was under a tornado watch, issued at 22:48 UTC and running to 06:00 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 Moderate Risk, with a 0.10 chance of a tornado within 25 miles. The outlook in force was issued at 01:00 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.

Storm Lake (SLB), 30 km from the path, in the two hours either side.

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

The Omaha radar (KOAX), 141 km away, was scanning. The volume nearest the touchdown began at 01:18 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.