A pair of areas of convection colluded to bring about heavy rainfall and sporadic severe storms into Iowa during the morning hours. Low level jet induced storms formed over southern South Dakota and worked their way eastward and eventually southeastward into Iowa, while convection over southern Minnesota was initiated along a southward moving boundary.  The two predominantly came together over northern Iowa before eventually moving straight southward through the state. Initially, the main results were sub-severe storms providing heavy rainfall, before organizing and tapping into enough instability to produce damaging winds and severe hail.
The environment within Iowa was fairly conducive to severe storm possibility, with elevated MUCAPE values around and in excess of 2000 J/kg, effective bulk shear of 30-40+ kts, and hail CAPE values around 600+ J/kg.  Fortunately, given that storms had grown upscale overnight, there was little to no isolated convection.

Thunderstorm Wind in ADAIR, IOWA
From 18-SEP-18 14:00:00 to 18-SEP-18 14:00:00 (CST-6)
Location: ADAIR
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Iowa DOT estimated winds at or above 60 mph along with hail a bit larger than peas.

Heavy Rain in CERRO GORDO, IOWA
From 18-SEP-18 07:09:00 to 18-SEP-18 09:09:00 (CST-6)
Location: VENTURA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 4 inches over the last 2 hours.

Heavy Rain in HANCOCK, IOWA
From 18-SEP-18 06:00:00 to 18-SEP-18 11:45:00 (CST-6)
Location: GARNER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public reported heavy rainfall of 3.25 inches ending this morning.

Thunderstorm Wind in WAPELLO, IOWA
From 18-SEP-18 12:00:00 to 18-SEP-18 12:00:00 (CST-6)
Location: OTTUMWA
Magnitude: 56.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a tree down on a camper, with the roof buckled. This is a delayed report and time estimated from radar.

Heavy Rain in HANCOCK, IOWA
From 18-SEP-18 06:30:00 to 18-SEP-18 09:30:00 (CST-6)
Location: KLEMME
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Public measured heavy rainfall of 3.19 inches via their home weather station.

Hail in POLK, IOWA
From 18-SEP-18 09:44:00 to 18-SEP-18 09:44:00 (CST-6)
Location: BONDURANT
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported brief penny sized hail.

Thunderstorm Wind in POLK, IOWA
From 18-SEP-18 10:20:00 to 18-SEP-18 10:20:00 (CST-6)
Location: FT DES MOINES
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported a tree down at Lincoln High School. This is a delayed report, time estimated from radar.

Hail in JASPER, IOWA
From 18-SEP-18 09:55:00 to 18-SEP-18 09:55:00 (CST-6)
Location: KELLOGG
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail.

Thunderstorm Wind in CASS, IOWA
From 18-SEP-18 13:50:00 to 18-SEP-18 13:50:00 (CST-6)
Location: ANITA
Magnitude: 52.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Iowa DOT RWIS station along I-80 west of Adair recorded wind gusts of 60 mph.