EF0 tornado, Stonega, Iowa, April 24, 2008

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

April 24, 2008

Touchdown

8:21 PM CDT (01:21 UTC)

Lifted

8:24 PM CDT (01:24 UTC)

On the ground

3 minutes

Path length

1.7 miles (2.7 km)

Path width

50 yards (46 m)

Deaths

0

Injuries

0

Property damage

$50,000

County

Hamilton County

Touchdown point

42.490, -93.710

Lift-off point

42.480, -93.680

Record number

0804241921-01

A strong push of moist and unstable air moved into Iowa during the day on the 24th. Surface temperatures warmed into the low to mid 70s over much of western and southern Iowa with dew point temperatures in the low to mid 60s. A cold front approached the state from the northwest during the evening. The airmass was quite unstable with surface based lifted indices around -4 C. and most unstable CAPE around 2000 J/kg. The shear was not real strong, but there was 30 to 40 kts of effective shear available. CAPE in the -10 to -30 C. layer of the atmosphere was in the 200 to 300 J/kg range with 700 to 800 J/kg of DCAPE available. The freezing level was relatively low, around 10,500 to 11,000 feet. Thunderstorms erupted ahead of the approaching cold front. Many of the storms produced hail with severe hail, with several reports of three quarter to one inch diameter hail reported from Audubon County northeast to Worth County, and east to Black Hawk County. Golf ball size hail fell in Wright County south of the Dows area. This was one of the larger reports. A 60 MPH wind gust was reported as the storms moved through Hardin County. One other report of high winds was received from Black Hawk County, where a pole shed was damaged. The LCL was relatively low, in the 500 to 1000 meter range. One tornado was reported north of Bancroft in Kossuth County early in the event. A second tornado touched down in Hamilton County and caused tree damage and minor shed damage on 3 farms. It was reported in an open area with little to no damage. The shear values were strongest in that area as well. The bulk of the severe weather moved out of the CWA just as a strong surface low pressure system begin to lift northeast along the advancing cold front. A new round of severe weather moved into southwest Iowa and then into parts of central Iowa. The severe weather from this second round was in the form of three quarter to one inch diameter hail. Over the northeast part of the CWA, the main problem was with flooding and flash flooding. Rainfall over the northeast quarter of the CWA was in the 3 to 4 inch range, with spotty amounts as high as 5 inches in the Denver area. Roads were washed out in numerous locations scattered from Tama County, north and northwest to Franklin County. The areal flooding transitioned to significant river flooding, which will be addressed in a separate entry.

A trained spotter sent a photo of a tornado and had driven back to the area where it was sighted. Tree damage and minor damage was noted on three farmsteads with the tornado track toward the southeast.

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.

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 01:00 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.

Webster City (EBS), 15 km from the path, in the two hours either side.

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

The Des Moines radar (KDMX), 84 km away, was scanning. The volume nearest the touchdown began at 01:19 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

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.