Tornadoes · United States · Iowa · 2017

EF0 tornado, Sharon Center, Iowa, July 21, 2017

This EF0 tornado ran 0.1 miles across Johnson County on July 21, 2017, touching down at 5:44 PM CDT and reaching 10 yards wide. It killed nobody.

The rating scale

Tracks are drawn in the color of the rating. The Enhanced Fujita scale rates the damage rather than measuring the wind: the speeds are what that damage is taken to imply.

  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.

The record

Rating
EF0
Date
July 21, 2017
Touchdown
5:44 PM CDT (22:44 UTC)
Lifted
5:45 PM CDT (22:45 UTC)
On the ground
1 minutes
Path length
0.1 miles (0.2 km)
Path width
10 yards (9 m)
Deaths
0
Injuries
0
County
Johnson County
Touchdown point
41.550, -91.620
Lift-off point
41.551, -91.618
Record number
1707211644-01

What the Weather Service recorded

Another round of convective storms fired along a stalled boundary and lasted overnight resulting in a major heavy rain and flooding event from 3 to over 8 inches of rain falling. Some storms become severe with damaging winds over 60 mph and isolated large hail.

The public reported a brief tornado moving northeast. After touching down, the tornado then lifted and dissipated.

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

The warnings

55 minutes of warning. NWS DVN issued a tornado warning for this county at 21:49 UTC, 55 minutes before the tornado touched down, in force until 22:45 UTC.

The county was under a severe thunderstorm watch, issued at 21:54 UTC and running to 02:53 UTC.

Issued (UTC)ExpiredProductOffice
20:51 UTC21:45 UTCSevere Thunderstorm WarningDVN
21:00 UTC13:32 UTCFlash Flood WatchDVN
21:39 UTC22:45 UTCSevere Thunderstorm WarningDVN
21:49 UTC22:45 UTCTornado WarningDVN
21:54 UTC02:53 UTCSevere Thunderstorm WatchDVN
22:16 UTC01:25 UTCFlash Flood WarningDVN
22:39 UTC23:12 UTCTornado WarningDVN

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 forecast that day

The Storm Prediction Center had this point in a Enhanced Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:52 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 air that afternoon

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.

Davenport, (KDVN), 12:00Z

10.7 hours before the tornado, 93 km from the path. July 21, 2017.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2017-07-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel lifted from the surface. Mixed-layer CAPE 81 joules per kilogram, CIN -302, lifted condensation level 1173 meters above ground. Wind barbs in knots down the right edge.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed. The warm shading is its CAPE, the cool shading the inhibition it has to break through.
HodographHodograph, Davenport, at 12:00Z on 2017-07-21The wind through the lowest 10 kilometers as a curve, rings every 10 meters per second labeled in knots. Zero to 1 km storm-relative helicity 125 square meters per square second, 0 to 6 km bulk shear 26 knots.1939Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km. RM and LM are the right and left moving storms Bunkers' method gives; the shaded area is the 0 to 1 km storm-relative helicity.
Mixed-layer CAPE
81 J/kg
Mixed-layer CIN
-302 J/kg
Surface CAPE
175 J/kg
Mixed-layer LCL
1173 m above ground
0-6 km bulk shear
26 kt
0-1 km bulk shear
25 kt
0-1 km storm-relative helicity
125 m²/s²
0-3 km storm-relative helicity
192 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0
0-3 km lapse rate
4.2 K/km

Open this sounding in Storm Lab

The radar

The Quad Cities radar (KDVN), 87 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.

What was reported nearby

Local storm reports within 60 km of the path, in the three hours either side.

Time (UTC)ReportWhereCountyRemark
21:15 UTCTSTM WND DMG5 Ene ParnellIowa, IALAW ENFOREMENT RELAYED ARE REPORT OF A TREE DOWN ON U AVE AND 270TH STREET. TIME OF THE EVENT WAS ESTIAMTED.
21:27 UTCHEAVY RAIN 1.41 Nnw ElyLinn, IAFELL IN 15 MINUTES.
22:03 UTCHAIL 0.252 N ElyLinn, IA
22:07 UTCTSTM WND DMGElyLinn, IALARGE TREE LIMBS DOWN OVER CAR. REPORT VIA KCRG FACEBOOK...TIME ESTIMATED.
22:09 UTCTSTM WND DMGWnw WilliamstownJohnson, IATREE BRANCHES DOWN. WIND ESTIMATED AT 50-60 MPH.
22:12 UTCHAIL 1Wnw WilliamstownJohnson, IA
22:17 UTCTSTM WND DMG1 S MartelleJones, IASHED DAMAGED AND LEANED OVER. REPORT VIA KCRG FACEBOOK.
22:19 UTCTSTM WND GST 53Iowa City Municipal AirJohnson, IA
22:22 UTCHAIL 14 Sw CoralvilleJohnson, IAREPORT VIA KCRG FACEBOOK.
22:29 UTCHAIL 0.882 W Iowa CityJohnson, IA
22:40 UTCHEAVY RAIN 1.47E SolonJohnson, IA
22:44 UTCTORNADO6 Ne KalonaJohnson, IAREPORT DELAYED - POSSIBLE TORNADO MOVING NORTHEAST - FUNNEL CLOUD APPEARED TO BRIEFLY TOUCH DOWN THEN LIFTED BACK INTO THE STORM
22:50 UTCFLASH FLOOD2 Sw Iowa CityJohnson, IASEVERAL INCHES OF WATER FLOWING OVER ROAD WITH MANHOLE COVERS BLOWN OUT.
23:05 UTCFLASH FLOODIowa CityJohnson, IAREPORT OF A FEW CARS STALLED IN SEVERAL INCHES OF PONDING WATER ON STREET IN TOWN.
23:09 UTCFUNNEL CLOUD1 N NicholsMuscatine, IAJUST SOUTH OF 155TH ST AND DAVIS AVE.
23:15 UTCTSTM WND GST 703 Nw BennettCedar, IADELAYED REPORT FROM LAST EVENING. WINDS SNAPPED 3 TREES.
23:17 UTCFUNNEL CLOUD3 S AtalissaMuscatine, IAREPORTED VIA ATALISSA PD NEAR 155TH AND KELLY AVE.
23:31 UTCTSTM WND DMGMuscatineMuscatine, IAA FEW 2 TO 4 INCH BRANCHES DOWN WITHIN THE CITY OF MUSCATINE. 2 5 TO 8 INCH TREE LIMBS DOWN FROM SOFT WOOD TREES.
23:38 UTCHEAVY RAIN 1.551 Sw North LibertyJohnson, IAFELL IN 90 MINUTES
23:38 UTCHEAVY RAIN 2.022 Nne Cedar RapidsLinn, IA

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

This ground now

The live radar over the trackEvery 2017 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

The other tornadoes of July 21, 2017

5 more were confirmed in the United States that day.

DateTimeRatingWherePath (mi)Width (yd)DeathsInjuriesDamage
July 213:45 PM CDTEF1Beltrami, MN2.8200$100,000
July 215:34 PM CDTEF0Clay, MN0.4100
July 215:52 PM CDTEF0Cheyenne, KS0.0400
July 217:19 PM CDTEF1Whiteside, IL3.7150$40,000
July 218:50 PM CDTEF0Oliver, ND0.225

What this means

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.

Sources

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.