EF1 tornado, Vinje, Iowa, May 4, 2012

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 mphthis tornado

   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

EF1

Date

May 4, 2012

Touchdown

5:52 PM CDT (22:52 UTC)

Lifted

5:54 PM CDT (22:54 UTC)

On the ground

2 minutes

Path length

0.8 miles (1.3 km)

Path width

90 yards (82 m)

Deaths

0

Injuries

0

County

Winnebago County

Touchdown point

43.487, -93.765

Lift-off point

43.486, -93.749

Record number

1205041652-01

3 damage points were recorded along this path by NWS DMX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF1. The highest wind the damage implies is 90 mph.

• Very old wooden barn. East and south walls collapsed--and the west and north walls caved in.
• Several roof panels lost from a small open sheet metal building.
• 81 x 48 ft outbuilding. West wall collapsed (maybe due to a tree falling on it?). West roof ripped off and deposited in grove of trees to the west. The south wall was crumbled, but the rest of the structure simply caved in, with each section relatively intact. Heaviest damage appears to be on the southern end of the building.

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

A nearly stationary frontal boundary remained draped across northwest Iowa. The airmass became very unstable with dewpoints surging into the 65 to 70 degree range. The wind flow at 850 mb was weak, only around 15 kts or so, but winds backed and were very convergent. Moisture pooled over northwest Iowa with precipitable water values increasing to around 1.4 inches by mid afternoon. The lifted index fell to between -5 and -10 C with CAPE rising to the 2000-3000 J/kg range. Downdraft CAPE was quite high, in the 800 to 1200 J/kg range. Ample CAPE was available in the -10 to -30 C layer of the atmosphere, between 400 and 800 J/kg. Unlike the previous day, significant shear was available for any storm development with 40 to 50 kts of effective shear. The freezing level was quite high for early May and was between 13,000 and 14,000 feet. Though high enough to limit hail, other parameters were sufficiently strong to overcome this. The LCL was fairly low with near storm environmental values around 750 meters. A line of strong to severe thunderstorms formed near the frontal boundary during the mid and late afternoon hours. The line moved and propagated east-southeast. High winds were common with the storms with wind speeds of up to 65 MPH or more. The storms also produced some quarter size hail. A tornado occurred in Winnebago County just south of the Minnesota line. It was about a mile long and was in open country. A short time later, a funnel cloud was observed in Worth County. After the main storms moved east, further thunderstorms developed behind the line. One became severe and produced golf ball size hail in Pocahontas County at Pocahontas.

Brief touchdown just south of the Minnesota border. Damaged a farm building and some trees.

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.

The county was under a severe thunderstorm watch, issued at 19:05 UTC and running to 00:57 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 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:53 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.

Forest City (FXY), 30 km from the path, in the two hours either side.

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

The Minneapolis radar (KMPX), 152 km away, was scanning. The volume nearest the touchdown began at 22:54 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 2012 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

11 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.