EF1 tornado, Medora, Iowa, April 14, 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

April 14, 2012

Touchdown

7:54 PM CDT (00:54 UTC)

Lifted

7:56 PM CDT (00:56 UTC)

On the ground

2 minutes

Path length

0.8 miles (1.4 km)

Path width

75 yards (69 m)

Deaths

0

Injuries

0

Property damage

$200,000

County

Warren County

Touchdown point

41.188, -93.670

Lift-off point

41.191, -93.654

Record number

1204141854-01

1 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 97 mph.

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

The first significant severe weather outbreak of the season took place during the afternoon and evening of the 14th with all modes of severe weather taking place. An upper level low pressure lifted northeast out of the southwest U.S. The upper level center, as well as the surface low, passed northwest of Iowa, across southeast South Dakota into Minnesota. Severe weather developed north of the warm front as it lifted north into Iowa. A cluster of severe storms formed over northeast Kansas and southeast Nebraska. These storms moved east-northeast along the warm front into Iowa, causing a considerable amount of severe weather. Severe weather parameters were fairly strong, however the dynamics of a 100 kt mid level jet and 60 kt low level jet made up the difference. Just prior to the storm development, CAPE values were around 4000 J/kg south of the development. Helicity was high, in the 300 to 500 range. There was a large amount of effective shear with 50 to 65 kts available. CAPE in the -10 to -30 layer of the atmosphere was in the 200 to 400 J/kg range, while downdraft CAPE was 600 to 800 J/kg. Plenty of low level moisture was drawn into the state on the strong low level jet. Precipitable water vales rose to 1.25 inches quite rapidly. The LCL level was relatively high, but given the dynmics was relatively easy to overcome. The LCL was just under 1000 meters at the beginning of the event. There were three tornadoes reported during the event. One was northwest of the Creston area in Union County. The most significant tornado caused high end EF2 damage to the far northwest corner of Creston. This tornado formed southwest of Cromwell at 1752 CST in Adams county and quickly tracked into northwest Creston around 1800 CST. EF2 damage occurred to the Greater Regional Medical Center and the Southwestern Community College campus. The tornado continued tracking to the northeast and damaged several farmsteads northeast of Creston before dissipating about 10 miles northeast of town at approximately 1815 CST. The wind strength was estimated to be 130 MPH. Significant damage occurred with uninsured damage alone near $2,000,000. A tornado touched down in Warren County east of New Virginia. The tornado caused damage to farm buildings and campers with a considerable amount of sheet metal left lying around. The EF1 tornado produced winds around 100 MPH. Many of the thunderstorms brought with them high winds and hail. The final tornado touched down in Mahaska County. The tornado was an EF1 tornado with a broad and intense rear flank downdraft south of the track. The AWOS site at the Oskaloosa airport in Mahaska County recorded a 97 MPH wind gust from the rear flank downdraft of the storm. Reports from the Emergency Manager indicated that damage at the airport was limited to two hangar doors and some damage to airport buildings. There were no planes on the field at the time. Numerous reports of hail larger than quarter size were received. Some of the larger hail included baseball size hail in Clarke County at Murray and numerous reports of golf ball size hail along the track of the severe cluster from Union County to Mahaska County. The same cluster of storms also produced very strong winds along its path. Numerous reports of 60 to 70 MPH winds were received all along the path. Numerous reports of tree and power line damage were received. The Des Moines metro area was hard hit with winds of up to 65 MPH causing considerable tree damage. At one time, 20,000 customers were reported without power. In Marion County a garage was destroyed and a house significantly damaged by the wind east of Knoxville. The storms also produced very heavy rainfall. Rainfall of 2 to 4 inches was reported at several locations. At the Des Moines International Airport, 1.10 inches of rain fell between 1630 and 1637 CST. This amount of rainfall in that short of period of time was a 100 year event. Fortunately it had been quite dry across the state, limiting the flash flood potential. Flash flooding was reported in Polk, Cass, and Madison Counties. Water was reported flowing one to two feet deep. Numerous reports were also received of street flooding and significant ponding.

Brief EF1 tornado confirmed by NWS damage survey. The tornado touched down three miles east of New Virginia and tracked about a mile to the east-northeast before dissipating. The tornado severely damaged several farm outbuildings and flipped several camper trailers. Wind speeds were estimated around 100 MPH.

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

17 minutes of warning. NWS DMX issued a tornado warning for this county at 00:37 UTC, 17 minutes before the tornado touched down, in force until 01:00 UTC.

The county was under a tornado watch, issued at 22:01 UTC and running to 05:00 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 Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:43 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.

Osceola (I75), 16 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), 60 km away, was scanning. The volume nearest the touchdown began at 00:55 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 2012 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

83 more were confirmed in the United States that day.

All 84 of them

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.