Without even looking at supporting variables, the setup for impactful weather could be gleaned from the general setup. A weak surface pressure system was slowly working its way across Iowa, situating its relevant boundaries primarily across southwest and southern Iowa. Within the warm sector, dew points were high in the low to mid 70s, especially considering afternoon air temperatures were only into the low 80s. Even north of the warm front and west of the cold front, the air mass was ripe for at least the potential for sustained rainfall with surface dew points in the upper 60s to low 70s.
Looking at the details, both heavy rainfall and tornadoes appeared in play. First, within the warm sector, MUCAPE values were within the 1000 to 2000+ J/kg neighborhood, lifted condensation levels were under 750 m, 0-3 km CAPE was around or in excess of 100 J/kg, effective shear was mediocre away form the fronts, and surface vorticity was present. North of and wrapping around the surface low, any support for severe weather was understandably lackluster given its location, but had the potential for sustained periods of moderate to heavy rainfall given the humid environment and slow moving surface low.
Given the setup, there were concerns for flooding issues, especially given previous rainfalls in the month and moist soils, and severe weather including funnel clouds and weak tornadoes. What transpired was heavy rainfall and flooding in and around northwest Iowa and then multiple funnel cloud and weak tornado reports in central and southeast Iowa. In total, 4 weak tornadoes were confirmed.

Heavy Rain in PALO ALTO, IOWA
From 20-JUN-18 13:30:00 to 20-JUN-18 16:35:00 (CST-6)
Location: EMMETSBURG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KICD relayed report heavy rainfall of about 3 inches since 2:30 pm.

Heavy Rain in PALO ALTO, IOWA
From 20-JUN-18 03:00:00 to 20-JUN-18 16:35:00 (CST-6)
Location: AYRSHIRE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KICD reported heavy rainfall of 3.40 inches since this morning.

Funnel Cloud in WEBSTER, IOWA
From 20-JUN-18 16:37:00 to 20-JUN-18 16:37:00 (CST-6)
Location: HARCOURT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a funnel cloud.

Tornado in BOONE, IOWA
From 20-JUN-18 13:28:00 to 20-JUN-18 13:29:00 (CST-6)
Location: BERKLEY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Tornado moved in from Dallas County.  This was a short segment that remained in agricultural fields with little damage before dissipating.

Funnel Cloud in HARDIN, IOWA
From 20-JUN-18 14:33:00 to 20-JUN-18 14:33:00 (CST-6)
Location: STEAMBOAT ROCK
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a rotating wall cloud with funnel.

Heavy Rain in PALO ALTO, IOWA
From 20-JUN-18 03:00:00 to 20-JUN-18 17:18:00 (CST-6)
Location: CURLEW
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KICD Radio relayed heavy rainfall report of 2.00 inches.

Funnel Cloud in MARION, IOWA
From 20-JUN-18 12:17:00 to 20-JUN-18 12:17:00 (CST-6)
Location: ATTICA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A funnel cloud was reported near the intersection of Hwy T17 and Hwy 5.

Heavy Rain in KOSSUTH, IOWA
From 20-JUN-18 02:30:00 to 20-JUN-18 17:22:00 (CST-6)
Location: HANNA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

WHO-TV relayed heavy rainfall report of 2.40 inches.

Tornado in GREENE, IOWA
From 20-JUN-18 13:20:00 to 20-JUN-18 13:24:00 (CST-6)
Location: SCRANTON
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.10K
Reported by: Storm Chaser

Tornado captured on video by Storm Chasers for duration of its life.  Remained in open agricultural fields with the only damage to crops north of Scranton.

Heavy Rain in PALO ALTO, IOWA
From 20-JUN-18 08:00:00 to 20-JUN-18 17:18:00 (CST-6)
Location: GRAETTINGER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KICD Radio relayed heavy rainfall report of 3.00 inches.

Tornado in HARDIN, IOWA
From 20-JUN-18 14:27:00 to 20-JUN-18 14:28:00 (CST-6)
Location: ELDORA
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Tornado from picture posted on social media.  Brief path across agricultural land east southeast of Eldora.

Flood in HUMBOLDT, IOWA
From 20-JUN-18 21:13:00 to 21-JUN-18 10:50:00 (CST-6)
Location: ST JOSEPH
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 250.00K
Reported by: Emergency Manager

Flooding was reported in the county with two roads still closed near Livermore. Deep washouts had occurred on some county roads in the northeastern portion of the county.

Tornado in WEBSTER, IOWA
From 20-JUN-18 13:43:00 to 20-JUN-18 13:45:00 (CST-6)
Location: LANYON
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.10K
Reported by: Trained Spotter

Brief tornado in southern Webster county east of Lanyon.  Tornado remained in open agricultural fields producing crop damage.  The tornado was captured on video by a trained spotter.

Heavy Rain in SAC, IOWA
From 20-JUN-18 00:45:00 to 20-JUN-18 18:48:00 (CST-6)
Location: SCHALLER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported heavy rainfall of 2.17 inches.

Funnel Cloud in DALLAS, IOWA
From 20-JUN-18 12:54:00 to 20-JUN-18 12:54:00 (CST-6)
Location: KENNEDY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported a rope funnel near the intersection of P57 and Highway 6.

Heavy Rain in WEBSTER, IOWA
From 20-JUN-18 13:00:00 to 20-JUN-18 15:00:00 (CST-6)
Location: COALVILLE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 1.95 inches between 2 and 4 pm.

Heavy Rain in HAMILTON, IOWA
From 20-JUN-18 06:00:00 to 20-JUN-18 20:31:00 (CST-6)
Location: ELLSWORTH
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 1.90 inches since 7 am this morning.

Flash Flood in KOSSUTH, IOWA
From 20-JUN-18 15:56:00 to 20-JUN-18 15:56:00 (CST-6)
Location: IRVINGTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Kossuth County Sheriff's office reported Highway 169 under water about 5 miles south of Algona.

Funnel Cloud in STORY, IOWA
From 20-JUN-18 17:25:00 to 20-JUN-18 17:25:00 (CST-6)
Location: GILBERT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter, via the Emergency Manager, reported a funnel cloud that may have touched down. This is a delayed report.

Flash Flood in CALHOUN, IOWA
From 20-JUN-18 02:29:00 to 20-JUN-18 06:20:00 (CST-6)
Location: FARNHAMVILLE
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 50.00K
Reported by: Law Enforcement

Law enforcement reported a one mile stretch of P21, Zearing Ave, closed due to water over the road. Depth was unknown at the time, but Calhoun County Sheriff's Deputy felt strongly enough that it needed barricades. The location was between 320th and 330th. Cause likely from Hardin Creek.

Flash Flood in HUMBOLDT, IOWA
From 20-JUN-18 15:52:00 to 20-JUN-18 21:20:00 (CST-6)
Location: LIVERMORE
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

County Sheriff's Office reported multiple roads covered in and around Livermore.

Flood in PALO ALTO, IOWA
From 21-JUN-18 01:16:00 to 21-JUN-18 10:50:00 (CST-6)
Location: EMMETSBURG
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 100.00K
Reported by: Law Enforcement

Water was flooding portions of US Hwy 18 east of Emmetsburg and in Cylinder. Water was also over Hwy 18 at the 4900 block of 370th St. and the 5500 block of 390th Street.

Flash Flood in HUMBOLDT, IOWA
From 20-JUN-18 17:04:00 to 20-JUN-18 21:20:00 (CST-6)
Location: LIVERMORE
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported water in basements along with street flooding in Livermore.

Tornado in DALLAS, IOWA
From 20-JUN-18 13:18:00 to 20-JUN-18 13:28:00 (CST-6)
Location: PERRY MUNI ARPT
Tornado F-scale: EF0
Property damage: 5.00K
Crop damage: 0.50K
Reported by: NWS Storm Survey

Tornado developed on east side of the Perry Airport in Dallas County before moving into a housing development.  There were several trees damaged or uprooted along with shingles removed from the roof of a nearby house.  The tornado tracked slowly north northeast with damage mainly to trees and crops along its path.  The tornado crossed from Dallas into Boone County before dissipating.

Flash Flood in KOSSUTH, IOWA
From 20-JUN-18 15:55:00 to 20-JUN-18 21:30:00 (CST-6)
Location: ST JOSEPH
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Kossuth County Sheriff's Office reported road submerged near Spring Valley Golf Course.

Flood in KOSSUTH, IOWA
From 21-JUN-18 02:36:00 to 21-JUN-18 10:50:00 (CST-6)
Location: WHITTEMORE
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 100.00K
Reported by: Law Enforcement

Water was flooding portions of Whittemore with sewage backing up into homes. Water continued to flow across portions of Hwy 18 in Kossuth County.

Flash Flood in WEBSTER, IOWA
From 20-JUN-18 03:40:00 to 20-JUN-18 06:20:00 (CST-6)
Location: KALO
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reporter water over the road of unknown depth at Elm and Nelson Ave in the town of Coalville. Enough rocks were washed on the road that it needed to be cleared away by heavy equipment.

Flash Flood in KOSSUTH, IOWA
From 20-JUN-18 20:45:00 to 21-JUN-18 02:50:00 (CST-6)
Location: WHITTEMORE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported about 1 foot of fast moving water across Highway 18.

Thunderstorm Wind in HUMBOLDT, IOWA
From 20-JUN-18 15:00:00 to 20-JUN-18 15:00:00 (CST-6)
Location: THOR
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 100.00K
Reported by: Trained Spotter

Trained spotter reported estimated wind gusts around 60 mph and that corn has been flattened.

Tornado in WAPELLO, IOWA
From 20-JUN-18 16:15:00 to 20-JUN-18 16:17:00 (CST-6)
Location: MUNTERVILLE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Tornado was captured on video in far western Wapello County.  The tornado was intermittent with little damage noted.

Flash Flood in WEBSTER, IOWA
From 20-JUN-18 03:15:00 to 20-JUN-18 06:20:00 (CST-6)
Location: KALO
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported water over the road at Riverside Trail and School Street just northeast of Otho. The water washed mud on the road and county officials needed heavy equipment to clear it off.

Flash Flood in PALO ALTO, IOWA
From 20-JUN-18 15:30:00 to 20-JUN-18 21:00:00 (CST-6)
Location: RODMAN
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 25.00K
Reported by: Law Enforcement

County Sheriff's Office reported fully water-covered roads in and around the town of Rodman.