EF1 tornado, Roberts to Williams, Iowa, August 31, 2014

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

August 31, 2014

Touchdown

8:40 PM CDT (01:40 UTC)

Lifted

8:45 PM CDT (01:45 UTC)

On the ground

5 minutes

Path length

4.6 miles (7.4 km)

Path width

205 yards (187 m)

Deaths

0

Injuries

0

Crop damage

$3,000

Counties

Webster and Hamilton counties

Touchdown point

42.311, -93.970

Lift-off point

42.341, -93.890

Record number

1408311940-01

28 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.

• Tornado entered corn field WSW of the destroyed hog building.
• Point at which the roof trusses began to fail.
• Eastern half of a hog confinement building was destroyed and deposited in the field to the east. Debris carried over a mile downstream in the tornado. Lowered DI and DOD since the building did have weaker, open walls.
• Tornado exiited the corn field at this location.

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

An unstable airmass was in place across Iowa with afternoon highs reaching well into the 80s, and dewpoint readings in the low to mid 70s. CAPE rose to 2000 to 3000 J/kg. Downdraft CAPE was around 900 to 1000 J/kg, with CAPE in the -10 to -30 C layer of the atmosphere in the 600 to 900 J/kg range. Precipitable water increased to around 1.75 inches. The freezing level was quite high at around 15,000 feet. Fairly strong shear was present with 40 to 50 kts of effective shear by late afternoon. A line of thunderstorms formed ahead of the cold front by late afternoon and moved east across the state through the evening hours. Hail with the storms was generally quite small. One inch diameter hail fell in Crawford County in Dow City. The primary severe events from this system were high winds that occurred as the MCS progressed across the state. Several locations reported gusts of 60 MPH or higher. An 80 MPH gust was reported in Guthrie County at Yale and Bayard. A 71 MPH wind gust occurred in Marion County. Heavy rainfall was also of significance with flash flooding in Crawford County. This was caused by a dam failure which flooded Highway 39. Three inches of rain fell in 50 minutes in Dallas County. There were numerous reports of around 2 inches of rain falling in Boone and Polk Counties. Water ponding and low-land flooding was common. One person was struck by lightning at the Denison Airport. The person received minor injuries. Funnel clouds were sighted in both Crawford and Boone Counties. Additional heavy rainfall events are included on 01 September 2014 entry.

Narrow tornado tracked just south of Highway 20 near Fort Dodge. Tornado produce crop damage and crossed Highway 169 before dissipating. Tornado was found and rated using high resolution satellite imagery.

Tornado traveled northeast for about half of its life before taking a sharp right turn and moving east southeast for remainder of track. There was some minor damage to grain bins. Tornado was found and rated using high resolution satellite imagery.

This small but potent tornado formed just over 3 miles north of Dayton and tracked nearly due east, destroying one hog confinement building and leaving a pronounced trail through multiple corn fields. The tornado weakened midway into its track, but still left a path 20 yards wide through several other corn fields before doing some minor tree damage at the end of its track. Tornado was surveyed but track lengthened after high resolution satellite imagery showed additional damage and path length.

Tornado formed about 5 miles southeast of Lehigh and traveled through primarily wooded areas of the Des Moines river valley. Tree damage was noted as well as crop damage in a few fields it crossed through. The tornado then continued on into Hamilton county. Tornado was found and rated using high resolution satellite imagery.

The tornado formed just northeast of Stratford and moved northeast producing crop and minor tree damage. This tornado merged with another tornado before dissipating. Tornado was found at rated using high resolution satellite imagery.

This tornado entered Hamilton county from Webster county. The tornado continued in rural areas of western Hamilton county producing crop and some tree damage. Tornado was found and rated using high resolution satellite imagery.

Tornado developed between Stratford and Stanhope and moved north northeast. The tornado produced mainly crop and minor tree damage with some shingles removed from a house near the track. This tornado merged with another tornado which began near Stratford before ending. Tornado was found and rated using high resolution satellite imagery.

Tornado develop about 1 mile northeast of Stanhope and moved northeast. The tornado did produce some minor tree damage along with crop damage along its path. The tornado was quite narrow but broadened considerably prior to its dissipation. Tornado was found and rated using high resolution satellite imagery.

This tornado moved into Hamilton county from Boone county. The tornado narrowed its path in Hamilton county producing crop damage and destroying a lean-to before dissipating. The tornado was found and rated using high resolution satellite imagery.

Brief tornado formed about 4 miles southwest of Kamrar and moved east southeast for its entire length. The tornado destroyed 3 grain bins at a farmstead along with crop damage. Tornado was found and rated using high resolution satellite imagery.

Brief tornado developed about 2.5 miles southwest of Kamrar and moved east southeast. This tornado took part of the roof off a confinement building along with crop damage along its path. Tornado was found and rated using high resolution satellite imagery.

Narrow tornado formed about 4.5 miles east of Kamrar and moved northeast. The tornado remained in open farmland for the duration of its life producing only damage to crops. Tornado was found and rated using high resolution satellite imagery.

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

13 minutes of warning. NWS DMX issued a tornado warning for this county at 01:27 UTC, 13 minutes before the tornado touched down, in force until 02:00 UTC.

The county was under a tornado watch, issued at 00:18 UTC and running to 02:47 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 00:59 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.

Webster City (EBS), 14 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), 68 km away, was scanning. The volume nearest the touchdown began at 01:38 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.