EF0 tornado, Bayard, Iowa, August 28, 2007

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

August 28, 2007

Touchdown

7:02 PM CDT (00:02 UTC)

Lifted

7:03 PM CDT (00:03 UTC)

On the ground

1 minutes

Path length

0.7 miles (1.2 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Property damage

$20,000

Crop damage

$10,000

County

Guthrie County

Touchdown point

41.850, -94.650

Lift-off point

41.850, -94.636

Record number

0708281802-01

A seasonally strong cold front moved southeast into the state during the afternoon and evening hours of the 28th. There was a strong contrast across the front with highs in the low 90s south of the front with dew points in the low to mid 70s, and temperatures in the 60s and 70s north of the front. The airmass was quite unstable with CAPE between 3000 and 4000 J/kg and lifted indices in the -6 to -8 C. range. There was sufficient shear in place and was in the 35 to 50 kt range. CAPE in the -10 to -30 C. layer of the atmosphere was 500 to 700 J/kg, however with freezing levels 15,000 to 15,500 feet hail was not realized in severe size at the ground level. The LCL was between 1000 and 1500 meters along the lead edge of the thunderstorms. As the front progressed southeast, a line of thunderstorms developed just ahead of the front. They developed quite rapidly as the cap was broken. The air was fairly dry in the lower levels leading to downdraft CAPE of 1000 to 1500 J/kg. In spite of the dry layer at low levels, precipitable water values were quite high, in the 1.5 to 1.7 inch range. Many of the storms remained below severe levels. An upper level vorticity max lifted northeast across eastern Nebraska into western Iowa during the late afternoon and evening hours. This intensified storms over eastern Nebraska, which moved into western Iowa. The storms became severe and produced high winds and several tornadoes from west central into central Iowa. The line took on a very evident bow echo as it moved through Crawford County, and that remained in tact as far east as Story County. Numerous reports of tree damage and power line damage were received, with winds of 60 to 70 MPH common. Winds were strong enough to partially blow over a utility pole near Jamaica in Guthrie County. A semitrailer truck was blown off off of County Road E-57 west of Kelly in Story County. Tornadoes touched down in Carroll and Greene Counties. They were short lived and were only on the ground for a short time in rural areas. One of them touched down in Carroll County north of Dedham, while a short time later a second touched down north of Coon Rapids downing utility poles. An aerial survey showed a very intermittent track, beginning about 3 miles north of Coon Rapids in Carroll County, continuing east for approximately 15 miles. It dissipated in Greene County just west of Cooper. Maximum path width was 50 yards. Crop damage and power poles were bent but no structures were significantly impacted. There was a two mile continuous swath of corn damage occurring about four miles west of Cooper with numerous meanders and turns. EF0 damage ended at approximately 1825 PM CST. Another tornado was on the ground for about 5 minutes in an intermittent track from southwest to south of Rippey. Minor roof damage was done and some windows were blown out by the tornado southwest of Rippey. Another tornado touched down in Guthrie County west of Bayard. An aerial survey showed a 3/4 mile long track that was embedded in the west to east outflow of the storm. A 50 yard wide track of damaged corn and a dozen trees downed at a farmstead were observed. A few shingles were blown off the house, but otherwise no other significant building damage was noted. The tornado was and EF0. Flash flooding was also a concern with flash flooding taking place in Calhoun and Wright Counties. Water was flowing over roads and into some basements. Heavy rainfall of 1 to 2 inches was common over already saturated ground. Nearly three and one half inches /3.42/ fell in a short time in the Rockwell City area.

An aerial survey showed a 3/4 mile long track embedded in west to east outflow. A 50 yard wide track damaged corn was observed. It also downed a dozen trees at a farmstead. A few shingles were blown off the house otherwise no building damage. The strength was EF0.

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 22:35 UTC and running to 01:34 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. The outlook in force was issued at 19:48 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 Des Moines radar (KDMX), 77 km away, was scanning. The volume nearest the touchdown began at 00:00 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 2007 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

4 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.