Note, a portion of this event began on August 31st (heavy rainfall namely) and carried over into September 1st.
The general setup for the day was less so for severe weather and more so for potential heavy rainfall. Synoptically, there were no major systems affecting the Plains, though a weak warm frontal boundary found itself slowly moving northward into the state, eventually giving way to a weak cold front later in the day. MUCAPE values ramped up throughout the day on the heels of strong warm air advection and moisture advection, reaching the 2000-3000+ J/kg during the evening and overnight hours. Effective bulk shear shear values were marginally supportive, sporadically reaching 30 to 40 knots. As hinted at previously, strong warm air advection and moisture advection at and around the 850 mb level boosted widespread lift and raised precipitable water values around and above 2.0 inches.
The primary result of the storms was heavy rainfall, though a few were able to form strong enough updrafts and/or organize long enough to produce brief periods of marginally severe hail and damaging winds. The greatest rainfall amounts were around and in excess of 4 to 6 inches.

Heavy Rain in RINGGOLD, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 05:50:00 (CST-6)
Location: BEACONSFIELD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 4.65 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Hail in GUTHRIE, IOWA
From 01-SEP-18 06:22:00 to 01-SEP-18 06:22:00 (CST-6)
Location: MENLO
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter sized hail and winds estimated up to 60 mph.

Heavy Rain in JASPER, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 07:00:00 (CST-6)
Location: KELLOGG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 3.60 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 530pm CST on August 31st.

Heavy Rain in DECATUR, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: LAMONI
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Lamoni Municipal Airport recorded heavy rainfall of 2.61 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in RINGGOLD, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: MT AYR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 3.00 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 200pm CST on August 31st.

Heavy Rain in POWESHIEK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: GRINNELL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 3.25 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in POWESHIEK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: GRINNELL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 3 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Hail in POWESHIEK, IOWA
From 01-SEP-18 01:33:00 to 01-SEP-18 01:33:00 (CST-6)
Location: MALCOLM
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

NWS Davenport relayed a trained spotter reported of quarter sized hail.

Flash Flood in TAMA, IOWA
From 01-SEP-18 08:00:00 to 01-SEP-18 09:30:00 (CST-6)
Location: TRAER MUNI ARPT
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

County Sheriff's Office relayed reports of fairly widespread flooding in and around Traer. Reports included water in basements, standing water over roads, sewers backing up, etc... Time recorded as report time. Unknown start time of the issues.

Heavy Rain in TAMA, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: TRAER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 6.57 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 1120pm CST on August 31st.

Heavy Rain in TAMA, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: DYSART
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 4.59 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Thunderstorm Wind in DECATUR, IOWA
From 01-SEP-18 02:15:00 to 01-SEP-18 02:15:00 (CST-6)
Location: LEON
Magnitude: 56.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported power lines down and a power outage in Leon. Basement flooding was also reported at some locations in the area. This is a delayed report.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: GILBERTVILLE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 2.43 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 08:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: WATERLOO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 2.70 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: CEDAR FALLS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 2.17 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in RINGGOLD, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 10:00:00 (CST-6)
Location: MT AYR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 4.00 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in STORY, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: AMES ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Ames Municipal Airport ASOS recorded heavy rainfall of 2.03 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in TAMA, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: TOLEDO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 3.07 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in UNION, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: THAYER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 4.65 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 05:15:00 (CST-6)
Location: MURRAY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 3.56 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 215pm CST on August 31st.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 09:00:00 (CST-6)
Location: HUDSON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 3.50 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 1130pm CST on August 31st.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: CEDAR FALLS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 2.23 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in TAMA, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: GARWIN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 2.71 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: OSCEOLA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 3.83 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in TAMA, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: TRAER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 6.57 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in BUTLER, IOWA
From 01-SEP-18 00:15:00 to 01-SEP-18 10:00:00 (CST-6)
Location: NEW HARTFORD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 2.04 inches.

Heavy Rain in WAYNE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:45:00 (CST-6)
Location: HUMESTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 2.24 inches. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in UNION, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 07:00:00 (CST-6)
Location: CRESTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported heavy rainfall of 4.5 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 200pm CST on August 31st.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:25:00 (CST-6)
Location: MURRAY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 3.80 inches. Due to database entry limitation, beginning time coded as midnight CST. Actual estimated start time of 220pm CST on August 31st.

Flash Flood in TAMA, IOWA
From 01-SEP-18 08:00:00 to 01-SEP-18 09:30:00 (CST-6)
Location: TRAER
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

County Sheriff's Office reported that the bridge on M Ave over Wolf Creek was under water due to the heavy rains overnight. Unknown beginning time of water over the bridge.

Heavy Rain in BLACK HAWK, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: (ALO)WATERLOO MUNI A
Property damage: 0.00K
Crop damage: 0.00K
Reported by: ASOS

Waterloo Regional Airport ASOS recorded heavy rainfall of 3.02 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 06:00:00 (CST-6)
Location: OSCEOLA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 3.87 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: MURRAY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 3.83 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Heavy Rain in CLARKE, IOWA
From 01-SEP-18 00:00:00 to 01-SEP-18 08:00:00 (CST-6)
Location: MURRAY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 3.95 inches over the last 24 hours. Due to database entry limitation, beginning time coded as midnight CST.

Hail in MARION, IOWA
From 01-SEP-18 01:33:00 to 01-SEP-18 01:33:00 (CST-6)
Location: KNOXVILLE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported penny sized hail.

Hail in GUTHRIE, IOWA
From 01-SEP-18 06:19:00 to 01-SEP-18 06:19:00 (CST-6)
Location: STUART
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported nickel sized hail.