EF0 tornado, Gerled to Stevens, Iowa, June 17, 2010

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

June 17, 2010

Touchdown

5:24 PM CDT (22:24 UTC)

Lifted

5:25 PM CDT (22:25 UTC)

On the ground

1 minutes

Path length

0.7 miles (1.1 km)

Path width

20 yards (18 m)

Deaths

0

Injuries

0

County

Kossuth County

Touchdown point

43.457, -94.029

Lift-off point

43.464, -94.019

Record number

1006171624-01

Warm and very humid air moved north into Iowa during the day on the 17th. Surface temperatures warmed into the mid 80s to low 90s, with dew point temperatures in the mid 70s to around 80 by mid afternoon. A weak cold front was approaching the state at the same time that a negatively tilted shortwave lifted northeast across the upper Midwest. The atmosphere became very unstable with lifted indices falling to around -9 C. CAPE rose to between 3000 and 4500 J/kg by late afternoon. Downdraft CAPE was around 1500 J/kg with available CAPE in the -10 to -30 C layer of the atmosphere between 800 and 1100 J/kg. With the humid airmass, precipitable water values were between 1.8 and 2 inches, resulting in a relatively low LCL level of 750 to 1000 meters. The freezing level was relatively high, around 14,500 feet. The shear was not all that strong, ranging from around 35 kts over northern Iowa to 20 over the southwest. Thunderstorms fired up initially during the mid to late afternoon hours. The storms consolidated into a solid line during the evening and advanced east-southeast across the state. During the early stages of the development, the thunderstorms produced several tornadoes. One touched down briefly near Lakota in Kossuth County along U.S. Highway 169. A second tornado tracked from southwest of Lakota to north of the city. A third tornado was on the ground briefly east of Rake in Winnebago County. The storms then transitioned into more of a wind and hail event. Due to the warm conditions aloft, most of the hail was only around in inch or so in diameter. Golf ball size hail fell in the Buffalo Center area of Winnebago County. The largest hail was a report of baseball size hail west of Ledyard in Kossuth County. Winds increased as the evening went on and the system accelerated. Tree damage was reported in several locations with winds gusting in the 60 to 70 MPH range.

Tornado touched down briefly west of Lakota, then lifted.

Tornado was spotted briefly.

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

26 minutes of warning. NWS DMX issued a tornado warning for this county at 21:58 UTC, 26 minutes before the tornado touched down, in force until 22:45 UTC.

The county was under a tornado watch, issued at 18:56 UTC and running to 01:52 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 Moderate Risk, with a 0.10 chance of a tornado within 25 miles, in the hatched area where significant tornadoes were expected. The outlook in force was issued at 20:06 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.

Fairmont Municipal (FRM), 38 km from the path, in the two hours either side.

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

The Minneapolis radar (KMPX), 159 km away, was scanning. The volume nearest the touchdown began at 22:24 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 2010 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

73 more were confirmed in the United States that day.

All 74 of them

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.