A setup for some rotating storms was in place over much of central and southern Iowa. A low pressure system situated northwest of the state slid to the northeast throughout the day, eventually moving into western and central Minnesota. Given its fairly mature frontal situation, an occluded front dropped into northwest Iowa with the warm front extending E/SE from central Iowa and the cold front dropping back to the SW. At the surface within the warm sector observations were favorable with temperatures into the mid 80s and dew points in the low to mid 70s. Looking in more detail, lifted condensation levels were quite low with values under 750 meters, MUCAPE values were modest in the 1000-3000 J/kg range, effective bulk shear was in excess of 40 kts, and effective storm relative helicity was around 200 m2/s2 to name a few. Resulting composite indices correctly highlighted an increased chance for supercells and tornadic potential as seen with supercell composite values in excess of 12 and significant tornado parameter values in the 3 to 5 range in the afternoon. All of which taking into account the general setup, understandably unable to account for storms potentially tapping into additional shear and helicity generated from rooting themselves along outflow boundaries.
The result was a sizable tornado outbreak across Iowa, including more than a dozen confirmed tornadoes. The tornadoes of most note occurred in the NE Des Moines Metro (specifically Bondurant), Pella, and Marshalltown. The Bondurant area actually experienced two tornadoes, which were concurrently on the ground, but fortunately only one actually caused damage (EF2) within town. The Pella tornado tacked on the north side of town, directly hitting the Vermeer plant, causing EF3 damage. The Marshalltown tornado entered the town from the NW and tracked into the downtown area before exiting and weakening east of town. Widespread damage was experienced in Marshalltown including to the Lennox plant and the County Courthouse.  All in all, while numerous injuries were experienced and millions of dollars of damage, no direct fatalities were reported from the tornadoes.

Tornado in MAHASKA, IOWA
From 19-JUL-18 15:13:00 to 19-JUL-18 15:24:00 (CST-6)
Location: PEORIA
Tornado F-scale: EF2
Property damage: 80.00K
Crop damage: 1.50K
Reported by: NWS Storm Survey

This tornado continued into Mahaska county from Marion county.  The tornado path was initially east in Mahaska county but a satellite tornado moved south on the backside of the parent rotation and the interaction turned the main circulation back to the southeast remaining in that heading for the remainder of the path.  The tornado did encounter one farmstead producing EF2 damage to the structures onsite before remaining in agricultural fields for the rest of its path.

Tornado in MAHASKA, IOWA
From 19-JUL-18 15:15:00 to 19-JUL-18 15:18:00 (CST-6)
Location: PEORIA
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.50K
Reported by: Storm Chaser

This was a satellite tornado which formed on the backside of the parent Pella tornado after it passed into Mahaska county.  This tornado was captured on video as it developed and the track is very apparent in high resolutions satellite imagery.  It did pass over a farmstead but damage to the structure was unknown.  Otherwise, it remained in open agricultural fields.

Tornado in MAHASKA, IOWA
From 19-JUL-18 15:50:00 to 19-JUL-18 15:53:00 (CST-6)
Location: OSKALOOSA ROTH ARPT
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.50K
Reported by: Other Federal Agency

Tornado developed south of Oskaloosa in rural cropland and did primarily crop damage on its southward path.  Path found using high resolution satellite imagery.

Funnel Cloud in POCAHONTAS, IOWA
From 19-JUL-18 11:08:00 to 19-JUL-18 11:08:00 (CST-6)
Location: ROLFE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a funnel cloud.

Funnel Cloud in STORY, IOWA
From 19-JUL-18 14:08:00 to 19-JUL-18 14:08:00 (CST-6)
Location: STORY CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported a funnel cloud northeast of Highway 17 and E18. Location is approximate.

Funnel Cloud in STORY, IOWA
From 19-JUL-18 14:13:00 to 19-JUL-18 14:13:00 (CST-6)
Location: MAXWELL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported a funnel cloud.

Funnel Cloud in POLK, IOWA
From 19-JUL-18 14:15:00 to 19-JUL-18 14:15:00 (CST-6)
Location: SANTIAGO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud just west of Mitchellville.

Funnel Cloud in STORY, IOWA
From 19-JUL-18 14:21:00 to 19-JUL-18 14:21:00 (CST-6)
Location: STORY CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud near I-35 and mile marker 101.

Funnel Cloud in WARREN, IOWA
From 19-JUL-18 14:23:00 to 19-JUL-18 14:23:00 (CST-6)
Location: HARTFORD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud.

Funnel Cloud in JASPER, IOWA
From 19-JUL-18 14:31:00 to 19-JUL-18 14:31:00 (CST-6)
Location: COLFAX
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported funnel cloud east of Highway 117 and S 60th St.

Funnel Cloud in JASPER, IOWA
From 19-JUL-18 14:35:00 to 19-JUL-18 14:35:00 (CST-6)
Location: MONROE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud near Highway 163 and mile marker 25.

Funnel Cloud in JASPER, IOWA
From 19-JUL-18 14:39:00 to 19-JUL-18 14:39:00 (CST-6)
Location: CLYDE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud near the intersection of Highway 65 and Highway 210.

Funnel Cloud in MARION, IOWA
From 19-JUL-18 15:03:00 to 19-JUL-18 15:03:00 (CST-6)
Location: OTLEY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud near Otley.

Funnel Cloud in MARION, IOWA
From 19-JUL-18 15:09:00 to 19-JUL-18 15:09:00 (CST-6)
Location: PELLA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a cone shaped funnel cloud.

Hail in MARION, IOWA
From 19-JUL-18 15:14:00 to 19-JUL-18 15:14:00 (CST-6)
Location: PELLA
Magnitude: 1.50 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported ping pong ball sized hail along the Jasper and Marion county lines.

Funnel Cloud in MARSHALL, IOWA
From 19-JUL-18 15:15:00 to 19-JUL-18 15:15:00 (CST-6)
Location: ALBION
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported a funnel cloud.

Funnel Cloud in MARSHALL, IOWA
From 19-JUL-18 15:17:00 to 19-JUL-18 15:17:00 (CST-6)
Location: BROMLEY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported a funnel cloud.

Funnel Cloud in MARSHALL, IOWA
From 19-JUL-18 15:17:00 to 19-JUL-18 15:17:00 (CST-6)
Location: CLEMONS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported a funnel cloud.

Thunderstorm Wind in WAPELLO, IOWA
From 19-JUL-18 16:12:00 to 19-JUL-18 16:12:00 (CST-6)
Location: (OTM)OTTUMWA INDSTRL
Magnitude: 62.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

The Ottumwa Municipal Airport ASOS recorded a 71 mph wind gust.

Hail in WAPELLO, IOWA
From 19-JUL-18 16:42:00 to 19-JUL-18 16:42:00 (CST-6)
Location: RUTLEDGE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Broadcast media reported quarter sized hail that fell between 5:42 and 5:45 pm.

Tornado in MARSHALL, IOWA
From 19-JUL-18 15:24:00 to 19-JUL-18 15:47:00 (CST-6)
Location: MARIETTA
Tornado F-scale: EF3
Property damage: 200.00M
Crop damage: 4.00K
Reported by: NWS Storm Survey

This tornado developed northwest of Marshalltown west of the little hamlet of Marietta.  The tornado traveled southeast on the western side of the Iowa River producing extensive crop and tree damage.  The tornado strengthened quickly and took on a wedge appearance as it entered northwest Marshalltown.  The tornado tracked more easterly as it entered town producing widespread EF1 and EF2 damage.  The tornado went directly through the business district of Marshalltown with EF2 and EF3 damage to many structures including the county courthouse which lost the spire off the clock tower.  The tornado continued east through housing areas before encountering the Lennox plant on the east side of town, producing EF3 damage once again.  The tornado began to weaken rapidly after this point and dissipated near power plant located on the east side of town.  The tornado produced a total of 22 direct injuries. An additional indirect injury resulted during the clean-up of storm debris when a tree fell on a man.

Tornado in JASPER, IOWA
From 19-JUL-18 14:18:00 to 19-JUL-18 14:24:00 (CST-6)
Location: COLFAX
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 1.00K
Reported by: Storm Chaser

Tornado remained in agricultural fields northwest of Prairie City for entire path length.

Tornado in STORY, IOWA
From 19-JUL-18 14:22:00 to 19-JUL-18 14:30:00 (CST-6)
Location: ROLAND
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Weak tornado developed just northeast of Roland and moved east northeast in rural agricultural fields.  Only damage was to crops.  Tornado path was obtained via high resolution satellite imagery.

Tornado in JASPER, IOWA
From 19-JUL-18 14:28:00 to 19-JUL-18 14:34:00 (CST-6)
Location: PRAIRIE CITY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.80K
Reported by: Storm Chaser

Tornado developed southeast of Prairie City and tracked to the southeast.  Remained in rural areas producing crop and tree damage before dissipating.

Tornado in STORY, IOWA
From 19-JUL-18 14:35:00 to 19-JUL-18 14:40:00 (CST-6)
Location: COLLINS
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.80K
Reported by: Storm Chaser

Weak tornado north of Collins tracked northeast in rural agricultural fields.  Damage only to crops.  Tornado path was obtained via high resolution satellite imagery.

Tornado in JASPER, IOWA
From 19-JUL-18 14:45:00 to 19-JUL-18 14:48:00 (CST-6)
Location: MONROE
Tornado F-scale: EF0
Property damage: 8.00K
Crop damage: 1.50K
Reported by: NWS Storm Survey

Tornado developed east of Monroe and tracked southeast for entire path.  Damage was mainly to trees and crops although a machine shed lost a small part of its roof near the start of the tornado.  There was impressive flattening of crops near the county line where path widened to 500 yards.  Tornado crossed from Jasper into Marion county.

Tornado in MARION, IOWA
From 19-JUL-18 14:48:00 to 19-JUL-18 14:52:00 (CST-6)
Location: OTLEY
Tornado F-scale: EF1
Property damage: 0.00K
Crop damage: 1.50K
Reported by: NWS Storm Survey

Path continued into Marion county from Jasper county.  In Marion county, the tornado remained in rural cropland damaging crops and trees.

Tornado in MARION, IOWA
From 19-JUL-18 14:56:00 to 19-JUL-18 14:58:00 (CST-6)
Location: OTLEY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Brief tornado east of Otley with little if any damage.  Reported by a storm chaser with path found using high resolution satellite imagery.

Tornado in MARION, IOWA
From 19-JUL-18 15:01:00 to 19-JUL-18 15:13:00 (CST-6)
Location: PELLA
Tornado F-scale: EF3
Property damage: 120.00M
Crop damage: 4.50K
Reported by: NWS Storm Survey

Tornado developed about 3 miles north of Pella and moved southeast for its entire length.  The tornado initially remained in rural areas just north and northeast of the town producing crop, tree and minor structural damage to houses.  The tornado began to intensify just northeast of town and shifted a house off of its foundation.  The tornado then encountered the Vermeer facility on the east side of town producing EF3 damage to one of the large buildings along with tossing numerous cars about the facility.  13 injuries occurred at the Vermeer facility with 6 requiring transport to the hospital.  The tornado then turned slightly eastward before passing into Mahaska county.

Tornado in MARSHALL, IOWA
From 19-JUL-18 15:11:00 to 19-JUL-18 15:13:00 (CST-6)
Location: BROMLEY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.10K
Reported by: Other Federal Agency

This was a brief tornado east of Clemons remaining in rural agricultural fields.  Damage was limited to corn and soybeans.  Path found using high resolution satellite imagery.

Tornado in WRIGHT, IOWA
From 19-JUL-18 13:30:00 to 19-JUL-18 13:37:00 (CST-6)
Location: EAGLE GROVE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.50K
Reported by: Emergency Manager

Tornado formed in rural Wright County east of Eagle Grove and moved northeast through open crop land.

Tornado in WRIGHT, IOWA
From 19-JUL-18 13:35:00 to 19-JUL-18 13:47:00 (CST-6)
Location: WOOLSTOCK
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.70K
Reported by: Emergency Manager

Tornado develop in rural southern Wright County east of Woolstock and traveled east northeast for the duration of the event.  The tornado remained in rural agricultural fields producing only crop damage.

Tornado in WRIGHT, IOWA
From 19-JUL-18 13:42:00 to 19-JUL-18 13:45:00 (CST-6)
Location: WOOLSTOCK
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.10K
Reported by: Other Federal Agency

Weak tornado developed in south central Wright county and moved northeast in rural agricultural areas.  Tornado was found using high resolution satellite data.

Tornado in POLK, IOWA
From 19-JUL-18 13:48:00 to 19-JUL-18 13:49:00 (CST-6)
Location: ENTERPRISE
Tornado F-scale: EF0
Property damage: 2.00K
Crop damage: 0.00K
Reported by: NWS Employee

A weak tornado developed just east of Interstate 35 in far eastern Ankeny and moved  northeast.  Damage was observed to several trees along with other minor damage to fencing and playground equipment as it passed through a small subdivision.  The tornado then moved into agricultural land before dissipating.

Tornado in POLK, IOWA
From 19-JUL-18 13:50:00 to 19-JUL-18 14:02:00 (CST-6)
Location: ENTERPRISE
Tornado F-scale: EF2
Property damage: 35.00K
Crop damage: 3.50K
Reported by: NWS Storm Survey

This tornado developed northwest of Bondurant concurrent with another tornado which developed due west of Bondurant.  This tornado remained in rural areas north of Bondurant traveling to the northeast.  Drone footage indicated impressive crop damage through corn and bean fields.  The tornado encountered a farmstead not long before  dissipating producing EF2 damage to trees.

Tornado in POLK, IOWA
From 19-JUL-18 13:51:00 to 19-JUL-18 14:00:00 (CST-6)
Location: BONDURANT
Tornado F-scale: EF2
Property damage: 250.00K
Crop damage: 1.00K
Reported by: NWS Storm Survey

The tornado developed about a mile and a half west of Bondurant.  The tornado initially traveled through agricultural fields.  The tornado entered western Bondurant and produced EF2 damage to a house on the western side of town.  The tornado weakened as it moved east through town with only EF0 damage on the east side of the community.  The tornado entered an agricultural field on the east side of town before dissipating.

Tornado in STORY, IOWA
From 19-JUL-18 13:52:00 to 19-JUL-18 13:57:00 (CST-6)
Location: STORY CITY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.50K
Reported by: Social Media

A weak tornado west of Story City reported via social media.  The tornado remained in open agricultural land with only crop damage.

Tornado in HAMILTON, IOWA
From 19-JUL-18 13:56:00 to 19-JUL-18 14:05:00 (CST-6)
Location: DUNCOMBE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 1.00K
Reported by: Storm Chaser

This tornado developed northwest of Blairsburg and moved northeast through agricultural land.  The tornado dissipated just prior to crossing County Highway D20.   Only damage was to crops.

Funnel Cloud in PALO ALTO, IOWA
From 19-JUL-18 10:45:00 to 19-JUL-18 10:45:00 (CST-6)
Location: CURLEW
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

NWS Chicago relayed a funnel cloud report from one of the trained spotters.