EF0 tornado, Napier, Iowa, May 11, 2014

1. EF065 to 85 mphthis tornado

   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 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

EF0

Date

May 11, 2014

Touchdown

10:44 PM CDT (03:44 UTC)

Lifted

10:46 PM CDT (03:46 UTC)

On the ground

2 minutes

Path length

1.7 miles (2.7 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$25,000

County

Boone County

Touchdown point

41.947, -93.763

Lift-off point

41.963, -93.739

Record number

1405112144-01

21 damage points were recorded along this path by NWS DMX, in the Damage Assessment Toolkit the survey teams carry. The strongest indicator was rated EF0. The highest wind the damage implies is 85 mph.

• Field scouring. Aerial photo courtesy of John McLaughlin, Iowa Helicopter. Used with Permission.
• Aerial photo courtesy of John McLaughlin, Iowa Helicopter. Used with Permission.
• Scouring continues NE. Aerial photo courtesy of John McLaughlin, Iowa Helicopter. Used with Permission.
• Trees twisted and large branches snapped.

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

Low pressure over Kansas moved northeast during the afternoon of the 11th into the morning of the 12th. By dawn on the 12th, the low was over northeast Kansas. A cold frontal boundary extended northeast from the low into northwest Iowa. The atmosphere became unstable and was strongly sheared. CAPE had increased to around 3000 J/kg by the late afternoon. Downdraft CAPE was in the 800 to 1200 J/kg range with available CAPE in the -10 to -30 C layer of the atmosphere around 600 J/kg. The lifted index was between -6 and -9 C. The freezing level had risen to around 14,000 feet. Deep moisture was drawn into the state on a 40 kt low level jet. Precipitable water values were in the 1.3 to 1.5 inch range. The LCL was quite low around 750 meters The atmosphere was strongly sheared with 55 to 65 kts of effective shear available. Thunderstorms formed along the cold front with initial development to the southwest of Iowa. The storms developed northeast into Iowa and became severe. There were numerous reports of high winds near 70 MPH, along with quarter to ping pong ball sized hail. Several funnel cloud reports were received as well. Flash flooding became a problem in Cass County near Atlantic. A NWS survey team found that 4 tornadoes touched down in Guthrie, Dallas and Boone Counties. One tornado formed south of Guthrie Center and tracked just over 10 miles northeastward and dissipated northeast of Lake Panorama where high end EF-1 and low EF-2 damage was found. The average path width was 240 yards with maximum wind speed of 115 MPH. A second tornado was an EF-1 tornado that formed on the west side of Lake Panorama and tracked east northeast to just south of Yale before dissipating. The third tornado was just north of Dallas Center in Dallas County and ended about 5 miles northwest of Granger just before reaching HWY 141. It was an EF-0 tornado with winds of 85 MPH. The fourth tornado was also an EF-0 occurring in Boone County where it touched down to the southeast of Luther.

Short-lived tornado that did some minor damage at a farmstead in rural Boone County before moving into open farmland.

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. One was issued for the county at another hour that day.

The county was under a tornado watch, issued at 00:49 UTC and running to 04:52 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, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 00:33 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.

The Des Moines radar (KDMX), 25 km away, was scanning. The volume nearest the touchdown began at 03:44 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 2014 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

35 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.