EF1 tornado, Mt Carmel to Manson, Iowa, May 10, 2015

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

May 10, 2015

Touchdown

7:10 PM CDT (00:10 UTC)

Lifted

8:00 PM CDT (01:00 UTC)

On the ground

50 minutes

Path length

23.3 miles (37.6 km)

Path width

700 yards (640 m)

Deaths

0

Injuries

0

Property damage

$1.0 million

Counties

Carroll and Calhoun counties

Touchdown point

42.147, -94.840

Lift-off point

42.448, -94.636

Record number

1505101810-01

45 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 100 mph.

• Damage associated with the second storm.
• grain bin - empty flipped. camper also flipped
• Multiple power poles snapped
• obvious road crossing at this point

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

A closed upper low lifted out to the west of Iowa with the surface low tracking northeast to near the Iowa-South Dakota border. A warm front extended southeast into Iowa and lifted north as the dry line pushed into western Iowa during the afternoon. The synoptic situation was fairly classic. The atmosphere was relatively unstable, though cloudiness limited that somewhat. CAPE values rose to 1500 to 2000 J/kg with a lifted index around -7 at the storms initiation. Downdraft CAPE was only 300 J/kg. There was 45 to 50 kts of effective shear however. CAPE in the -10 to -30 C layer was around 500 J/kg, with a freezing level around 12,000 feet. The parameters were favorable for potential tornado development with the LCL only 750 meters and 50 to 100 J/kg of CAPE in the zero to 3 km layer with steep lapse rates. Thunderstorms formed in an arc across western Iowa and quickly produced gusty winds and small hail. The cells tracked north as the line lifted northeast. Numerous reports of tornadoes were received. The reports were from the same tornado. Debris was reported with the tornado in Carroll County. Damage as done in the Lake City area of Calhoun County by a tornado, reported to be 1/4 mile wide by then. The tornado touched down northwest of Lidderdale and tracked northeast, striking the west side of Lake City. The tornado continued passing through rural Calhoun County and hit some power poles on the west side of Rockwell City before lifting about 2 miles north of Rockwell City in rural Calhoun County. Much of the damage included leaning power poles, tree damage and uprooted trees. In the town of Lake City, the roofing material was removed from the High School, and the roof was removed from a double-wide manufactured home and a warehouse building north of town. The tornado was of EF1 strength with winds of 100 MPH. The track was 23.5 miles long. Additional thunderstorms produced hail and high winds. An 80 MPH wind gust was reported west of Glidden, a machine shed was destroyed in Audubon County, and a weak shed was blown over in Cass County. Winds were measured at 65 MPH in Pocahontas. A strong storm moved through the Lake City area following the tornado and produced baseball size hail and destroyed a farm outbuilding west of Lidderdale.

Debris on the ground. Tornado continued into Calhoun County.

Tornado moved from Carroll County into Calhoun County. It moved across the western side of Lake City, doing EF1 damage to houses and the high school. It remained in rural areas of Calhoun County for the remainder of it's path, broadening as it went along. The tornado lifted shortly before crossing Highway 20.

This was a broad and brief tornado that caused little to no damage. Reported by a spotter and likely track found in satellite data.

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 Enhanced Risk, with a 0.10 chance of a tornado within 25 miles. The outlook in force was issued at 19:43 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.

Carroll (CIN), 28 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), 105 km away, was scanning. The volume nearest the touchdown began at 00:02 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 2015 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

23 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.