EF1 tornado, Thompson to Leland, Iowa, June 7, 2008

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 7, 2008

Touchdown

3:41 PM CDT (20:41 UTC)

Lifted

3:50 PM CDT (20:50 UTC)

On the ground

9 minutes

Path length

6.4 miles (10.2 km)

Path width

150 yards (137 m)

Deaths

0

Injuries

0

Property damage

$250,000

Crop damage

$10,000

County

Winnebago County

Touchdown point

43.350, -93.780

Lift-off point

43.380, -93.660

Record number

0806071441-01

Low pressure developed over Kansas with a strong southerly flow of very moist air streaming into Iowa ahead of it. Surface temperatures warmed into the 80s with dew point readings in the low to mid 70s. A semi-stationary front extended northeast from the low, across northern Iowa during the afternoon into the evening hours. The atmosphere became very unstable with MUCAPE in the 4500 to 5000 J/kg range by mid afternoon and lifted indices around -7 C. The shear was quite high, between 40 and 70 kts. Downdraft CAPW was between 1000 and 1300 J/kg with cape in the -10 to -30 C. layer of the atmosphere around 400 J/kg. The LCL was in the 750 to 1000 meter range, with the lowest over north central Iowa. With the exception of one hail report of 3 inch diameter hail report in north central Iowa, hail size was somewhat limited by the freezing level of 15500 to 16500 feet. A very strong transport of moisture took place on a 50 to 75 kt 850 mb jet. Precipitable water values soared to 1.6 to 1.9 inches by evening. During the initial phase of the severe event, high winds and hail were reported along the line of thunderstorms that formed from northern into west central Iowa. There were four reports of tornadoes in Worth, Winnebago and Cerro Gordo Counties during the afternoon hours of the 7th. This was with the initial round of storms. One of the tornadoes in Winnebago County destroyed a hog confinement building containing 3500 hogs. Several of them were killed and the remaining hogs needed to be taken to slaughter. The event transitioned into a flooding event overnight, then tornadoes began again during the afternoon of the 8th. A tornado touched down in Taylor County. Windows were blown out of houses there and several trees were twisted and blown down around the house. A pole shed was completely destroyed south of Ferguson in Marshall County. A stronger tornado was on the ground north to northeast of Ottumwa. A home lost a roof, with a wall of one room partially collapsed by the tornado. Several trees were also downed around the home. The event transitioned into a major Flood/Flash Flood event during the evening and early morning hours with many locations reporting 1 to 2 inches of rainfall, and spotty amounts of around 5 inches in just a few hours time. The line moved very little for a period of several hours. During the predawn hours, the line became broad and weakened to generally below severe limits. A new round of thunderstorms from Nebraska, which was the southwest part of the extensive line, moved into west central and southwest Iowa. The storm generally remained below severe levels for the most part, but they did produce very heavy rains. Another line of thunderstorms formed/re-intensified along the frontal boundary by the early afternoon hours. Initially, the storms produced strong winds and some small hail. As they moved southeast, several reports of high winds to near 70 MPH and a few reports of tornadoes were received. The most significant weather feature with this event was the heavy rainfall. The antecedent soil conditions in Iowa were extremely wet, such that flash flooding was caused by rainfall of an inch or more in an hour, even in rural areas. Heavy rainfall of 3 to 6 inches occurred in a broad swath extending from west central into north central, and parts of central and northeast Iowa. This resulted in widespread flash flooding. Eventually, the rain lead to major to record flooding along many of the rivers in the state. At one point or another, about 40 of the DMX 51 counties in the CWA were under flash flood warning. The situation was very serious over the north central and northeast counties. A levy was breached in the Mason City area as the Winnebago River rose to 3 feet over the record stage. The city was inundated by water. The water treatment plant was under water and non operational, all power was lost to the power grid in the city. The river cut a new channel and changed course into the downtown area. In the New Hartford area, a dam broke on Beaver Creek, resulting in the water level rising 2 feet above the all-time record level. High water along the mainstem Cedar River also caused communities to lose water. Nashua lost water as the water plant became flooded. Flooding along the Shell Rock River resulted in water supply loss in the town of Rockford. There was one death that resulted from the flooding. A 33 year old man died as he drove into flood waters in Interstate 35 at mile post 141 in Hamilton County. A second death occurred in Wright County as a 50 year old male farmer near Galt was sucked into a culvert by flood waters as he checked the field tiles in his farm field.

Rain wrapped tornado. Tornado hit hog confinement building and destroyed it. A barn was also damaged.

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

7 minutes of warning. NWS DMX issued a tornado warning for this county at 20:34 UTC, 7 minutes before the tornado touched down, in force until 21:00 UTC.

The county was under a tornado watch, issued at 17:17 UTC and running to 00:40 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 20:01 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.

Mason City (MCW), 40 km from the path, in the two hours either side.

From the Iowa Environmental Mesonet's archive of airport observations.

The Minneapolis radar (KMPX), 165 km away, was scanning. The volume nearest the touchdown began at 20:41 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 2008 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

30 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.