EF0 tornado, Bridgewater, Iowa, March 22, 2011

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

March 22, 2011

Touchdown

5:42 PM CDT (22:42 UTC)

Lifted

5:44 PM CDT (22:44 UTC)

On the ground

2 minutes

Path length

1.0 miles (1.6 km)

Path width

30 yards (27 m)

Deaths

0

Injuries

0

County

Adair County

Touchdown point

41.260, -94.644

Lift-off point

41.267, -94.627

Record number

1103221642-01

4 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 89 mph.

• Canopy to an outdoor storage building was damaged. Industrial machinery tipped over.
• Damage to outdoor storage bins.
• Brief touchdown. No damage reported.

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

Low pressure formed to the west of Iowa and during the morning it was located over central Nebraska with a warm front extending east-southeast across southern Iowa. The low advanced east during the day as the warm front moved little. Initially, the airmass was capped by a strong elevated mixed layer. During the late afternoon and early evening hours, a strong upper level short wave moved into the area. Temperatures aloft fell rapidly, destabilizing the atmosphere. Meanwhile, a strong low level jet formed ahead of the approaching low with winds of 40 to 50 kts. This helped to bring in moisture and increased the precipitable water values to around an inch over much of Iowa. By late afternoon, most unstable CAPE values were in the 1000 to 2000 J/kg range. Surface lifted indices were not all that impressive, however the elevated values were in the -3 to -6 C range. The atmosphere was strongly sheared with 50 to 70 kts of available shear. The LCL values were quite low as strong heating had not taken place during the day. LCL heights were between 500 and 1000 meters. Downdraft CAPE was quite high with values just ahead of the convection between 700 and 1000 J/kg. The freezing level was quite low, near 11,000 feet, and available CAPE in the -10 to -30 C layer of the atmosphere was between 400 and 500 J/kg. Thunderstorms fired along and just south of the surface low along a dry line ahead of the associated cold front. Convection was strong and moved rapidly northeast. There were two areas of thunderstorms. A line of strong to severe thunderstorms formed just ahead of the cold front, with more isolated severe convection forming ahead of the main line. There were numerous reports of tornadoes, mainly with the leading convection. The three strongest tornadoes took place west to northwest of Creston in Union County, and northwest to north of Winterset in Madison County and southeast of Massena in Cass County. The tornado in Cass County touched down approximately 1/2 mile east of the intersection of Iowa Hwy 148 and County Hwy G61. It damaged the canopy to an outdoor storage building and tipped over some industrial machinery. It continued northeast and damaged a structure...and caused some minor additional damage to a farmstead north of the intersection of County Hwy G61 and 760th St. Finally, it damaged some outdoor storage bins south of the intersection of County Hwy G53 and 770th Street. It then lifted. The same parent storm continued northeast and a small EF0 tornado touched down briefly near Bridgewater in Adair County. In Madison County, A tornado touched down 10 miles northwest of Winterset. The tornado was characterized by a large circulation up to 0.8 tenths of a mile wide (Iowa Helicopter) and generally of EF1 (90-100 MPH wind) strength. Eyewitnesses report the tornado was rain wrapped and difficult to distinguish from the rain shield as it approached them from the southwest. The tornado moved across several residences, many of which had broken windows and some roof damage along with significant tree and outbuilding damage. One newly constructed house that was near completion, slid off its foundation with the metal tie down straps either sheered off or pulled out of the concrete foundation. This damage is consistent with winds around 120 MPH which are EF2 strength. The roof structure remained intact and was aided by hurricane clips. Several other residences suffered partial roof removal with no hurricane clips noted. One other location had numerous trees either uprooted or topped and several outbuildings with the roofs blown off. Objects near the ground did not suffer near as much damage suggesting the peak winds at this location were just off the surface. The tornado lifted around 10 miles north northeast of Winterset or 5 miles south of Van Meter around 1735 CST. The tornado in Union County was not as intense, with damage there relatively minor. In addition to the line of severe thunderstorms, there was also convection that developed to the north of the low pressure track. Outside of the tornadic storms, the primary mode of severe weather was hail. There were reports of hail with most of the storms as they passed, with several reports of hail from quarter up to golf ball in size. Hail caused damage to roofs and vehicles. Fortunately, the crops had not been planted so there wasn't any agricultural loss. A few reports of strong winds were received with wind gusts in the 60 to 65 MPH range. Some tree and power line damage occurred, but it was not widespread. Heavy rainfall caused minor flooding in the metropolitan Des Moines area. A rainfall of 1.73 inches in under 2 hours in West Des Moines resulted in minor urban flooding along EP True Parkway. Water was standing 1 to 2 feet deep in low drainage areas along the parkway. There were also numerous reports of urban flooding around the city with water standing in intersections. As the thunderstorms moved through Butler County, lightning struck a barn near Shell Rock. The lightning caused damage to the barn and a minor fire.

Tornado near Delta Ave and Highway 92. Brief touchdown. This tornado was from the same parent cell the produced an EF1 tornado in Cass County.

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

40 minutes of warning. NWS DMX issued a tornado warning for this county at 22:02 UTC, 40 minutes before the tornado touched down, in force until 22:45 UTC.

The county was under a tornado watch, issued at 19:05 UTC and running to 02:00 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 0.10 chance of a tornado within 25 miles. The outlook in force was issued at 19:37 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), 92 km away, was scanning. The volume nearest the touchdown began at 22:43 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

8 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.