A nearly station boundary draped itself across northern Iowa, oriented east-west on the evening of the 27th and allowed isolated supercells and multi cellular storms to initiate and in some cases train/develop over the same area for a number of hours. In total, severe weather (damaging winds, funnel clouds, tornadoes), heavy rain, and flooding occurred.
The portions of northern Iowa that experienced the severe and hazardous weather resided just south of the surface boundary and included the following environment: SB/MUCAPE in excess of 2000 j/kg, LCLs under 1000m, effective bulk shear around/in excess of 30 kts, precipitable water values in excess of 1.8 inches, supercell composite values in excess of 12, effective SRH around 200 m2/s2, and 0-3km SRH around 200-300 m2/s2.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 15:54:00 to 27-AUG-21 15:54:00 (CST-6)
Location: MESERVEY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Small tree limbs down at one to three inches in diameter. Power line was knocked down as well. Report via picture on social media.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 16:08:00 to 27-AUG-21 16:08:00 (CST-6)
Location: MASON CITY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency Manager reports a few tree limbs down around town with some damage to power lines. Time estimated via radar.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 16:12:00 to 27-AUG-21 16:12:00 (CST-6)
Location: HURLEY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reports trees down, some were healthy trees and other not. Time estimated via radar.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 16:16:00 to 27-AUG-21 16:16:00 (CST-6)
Location: HURLEY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reports tree damage south of Swaledale area. Time estimated via radar.

Funnel Cloud in CERRO GORDO, IOWA
From 27-AUG-21 16:27:00 to 27-AUG-21 16:27:00 (CST-6)
Location: ROCKWELL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A funnel cloud was reported north of Sheffield. The funnel cloud was low but unclear if it was in contact with the ground.

Funnel Cloud in CERRO GORDO, IOWA
From 27-AUG-21 16:42:00 to 27-AUG-21 16:42:00 (CST-6)
Location: DOUGHERTY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Funnel cloud reported 2 miles northwest of Dougherty, with uncertainty as to whether it was in contact with the ground.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 19:12:00 to 27-AUG-21 19:12:00 (CST-6)
Location: ROCK FALLS
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Delayed report with areal photography showing extensive wind damage to crops about 2 miles north of Rock Falls. Time estimated via radar.

Heavy Rain in WORTH, IOWA
From 27-AUG-21 00:00:00 to 27-AUG-21 19:57:00 (CST-6)
Location: GRAFTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A rainfall report of 5.83 inches since midnight.

Flash Flood in WORTH, IOWA
From 27-AUG-21 20:48:00 to 28-AUG-21 01:00:00 (CST-6)
Location: NORTHWOOD
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water was several inches deep and completely covering 13th Street South in Northwood.

Flash Flood in WORTH, IOWA
From 27-AUG-21 21:12:00 to 28-AUG-21 01:00:00 (CST-6)
Location: GRAFTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water was several inches deep flowing over Yarrow Avenue near the intersection of 410th Street.

Flash Flood in WORTH, IOWA
From 27-AUG-21 21:22:00 to 28-AUG-21 01:00:00 (CST-6)
Location: GRAFTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Water two to three feet deep flowing up to the road on south end of town as well as approaching a residence. Three to six inches of water flowing over road. Report via social media courtesy of KAAL TV.

Flash Flood in WORTH, IOWA
From 27-AUG-21 21:34:00 to 28-AUG-21 01:00:00 (CST-6)
Location: GRAFTON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Water several inches deep flowing over the road near the intersection of Ulmus Avenue and 410th Street east of Kensett.

Thunderstorm Wind in STORY, IOWA
From 28-AUG-21 02:15:00 to 28-AUG-21 02:15:00 (CST-6)
Location: ONTARIO
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Reports of numerous tree branches and some larger trees down.

Thunderstorm Wind in CRAWFORD, IOWA
From 28-AUG-21 04:12:00 to 28-AUG-21 04:12:00 (CST-6)
Location: DOW CITY
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Delayed report of several large trees down early Saturday morning. Time estimated via radar.

Heavy Rain in WORTH, IOWA
From 27-AUG-21 06:50:00 to 28-AUG-21 06:50:00 (CST-6)
Location: GRAFTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

A 24 hour rainfall total of 4.21 inches.

Heavy Rain in WORTH, IOWA
From 27-AUG-21 07:07:00 to 28-AUG-21 07:07:00 (CST-6)
Location: GRAFTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

A 24 hour rainfall total of 3.62 inches.

Heavy Rain in HARDIN, IOWA
From 27-AUG-21 23:00:00 to 28-AUG-21 08:00:00 (CST-6)
Location: IOWA FALLS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Midnight to 9am rain total of 2.25 inches.

Tornado in CERRO GORDO, IOWA
From 27-AUG-21 16:06:00 to 27-AUG-21 16:12:00 (CST-6)
Location: CLEAR LAKE
Tornado F-scale: EF0
Property damage: 1.00K
Crop damage: 0.50K
Reported by: Emergency Manager

Report of a tornado west of Burchinal with a supercell in Cerro Gordo county.  Tornado path confirmed using high resolution satellite imagery.  Damage was mostly to crops although some minor tree damage occurred at a couple of farmsteads.

Tornado in CERRO GORDO, IOWA
From 27-AUG-21 16:35:00 to 27-AUG-21 16:41:00 (CST-6)
Location: DOUGHERTY
Tornado F-scale: EFU
Property damage: 1.00K
Crop damage: 0.50K
Reported by: Emergency Manager

Tornado occurred southeast of Rockwell and moved east southeast.  The tornado path was  confirmed using high resolution satellite imagery.  No damage indicators were impacted, hence the EFU rating.

Funnel Cloud in HANCOCK, IOWA
From 27-AUG-21 15:45:00 to 27-AUG-21 15:45:00 (CST-6)
Location: KLEMME
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Time and location estimated by radar. Report via social  media.

Thunderstorm Wind in CERRO GORDO, IOWA
From 27-AUG-21 15:52:00 to 27-AUG-21 15:52:00 (CST-6)
Location: CLEAR LAKE
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Tree damage and power outages around the Clear Lake area. Time estimated via radar.