EF1 tornado, Halbur to Willey, Iowa, June 26, 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 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

June 26, 2011

Touchdown

8:40 PM CDT (01:40 UTC)

Lifted

8:43 PM CDT (01:43 UTC)

On the ground

3 minutes

Path length

2.4 miles (3.8 km)

Path width

100 yards (91 m)

Deaths

0

Injuries

0

Property damage

$100,000

Crop damage

$10,000

County

Carroll County

Touchdown point

41.960, -94.980

Lift-off point

41.961, -94.934

Record number

1106261940-01

A dynamic pattern was once again in place over the central U.S. A strong surge of moisture took place during the day on the 26th, with precipitable water values rising to over 2 inches by evening. The airmass became very unstable with the lifted index falling to around -8 and CAPE in excess of 4000 J/kg. The atmosphere was quite warm with the freezing level between 15,000 and 16,000 feet. CAPE in the -10 to -30 C layer of the atmosphere was around 600 J/kg. Downdraft CAPE was quite high, in the 1200 to 1500 J/kg range. Considerable shear was available with shear in the 50 to 65 kt range. Meanwhile, a strong mid level trough of low pressure approached the central U.S. along with a moderate cold front approaching from the northwest. During the night, the low level jet increased to 70 kts, further feeding the thunderstorms. A large complex of thunderstorms developed across South Dakota into Nebraska. It moved southeast into the rich air over Iowa and accelerated, becoming a derecho. A large area of high winds developed with widespread wind gusts of 60 to 75 MPH, mainly over the southwest half of the CWA. The storms also produced hail at most locations as it passed. Most of the hail was around an inch or so in diameter. A smaller area of thunderstorms formed over southeast Iowa, ahead of the main area. These storms produced hail up to golf ball in size, along with 60 MPH winds during the early evening. The largest hail reported was 2 inches in diameter in Cincinnati in Appanoose County. The storms produced copious rainfall in spite of their rapid movement. Flash flooding was reported in Union, Adair, Davis, and Adams Counties. For the most part the flash flooding was relatively minor, limited to water flowing rapidly over roads. In Davis County at Bloomfield, water blew off manhole covers and was deep enough to nearly reach the tops of car roofs. The thunderstorm winds caused widespread damage to trees and power lines. A semi-truck was overturned on Highway 141 west of Woodward by the winds. Another was overturned in Carroll County on U.S. highway 30. A high wind event also took place with the storm complex as a wake low formed. Strong easterly winds developed with wind speeds in the 60 to 75 MPH range common. The strongest winds occurred in Webster County at Callendar. Winds of 80 to 90 MPH blew down mailbox posts, blew down trees onto houses, and picked up a swing set and blew it through the window of a house. Tree and power line damage was quite widespread over a 7 county area. One tornado touched down in Carroll County south of Halbur. A narrow swath of damage occurred from about one quarter mile south of the intersection of Granite Ave and County Road E53, with the roof blown off a hog confinement building just southeast of the intersection. Minor damage continued along a path 2.5 miles long to the east with another roof partially blown off of a Morton building just southwest of the intersection of County Road E53 and Ivy Ave. The tornado lifted about one quarter of a mile southeast of the intersection.

An EF1 tornado was on the ground for a brief time with a path length of 2.5 miles due east. Width was up to 100 yards with peak wind estimated at around 95 mph. A roof was blown off a hog confinement building and Morton building with other damage in between.

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 severe thunderstorm watch, issued at 22:00 UTC and running to 03:57 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 01:01 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), 105 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 2011 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

6 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.