Pre-frontal (warm sector) and cold frontal forced thunderstorms (linear and multicellular) moved across portions of northern Iowa during the evening hours of August 20th producing three tornadoes and heavy rainfall.
Environmental conditions were favorable for strong to severe storms, including MUCAPE in excess of 3000-4000 J/kg, bulk effective shear around 30 kts ahead of and around 40 kts along the front, 0-3 km bulk shear around 30 to 35 kts roughly perpendicular to storms (especially those ahead of the front), and LCLs around and under 1000m.

Tornado in POCAHONTAS, IOWA
From 20-AUG-21 19:03:00 to 20-AUG-21 19:05:00 (CST-6)
Location: BLANDEN
Tornado F-scale: EFU
Property damage: 0.00K
Crop damage: 0.50K
Reported by: Other Federal Agency

Weak tornado southwest of Palmer remained in rural agricultural fields.  Path was determined using high resolution satellite imagery.  No damage indicators were impacted, hence the EFU rating.

Tornado in HUMBOLDT, IOWA
From 20-AUG-21 19:19:00 to 20-AUG-21 19:22:00 (CST-6)
Location: UNIQUE
Tornado F-scale: EFU
Property damage: 0.00K
Crop damage: 1.00K
Reported by: Other Federal Agency

Weak tornado southwest of Rutledge remained in rural agricultural fields.  Path was determined using high resolution satellite imagery.  No damage indicators were impacted, hence the EFU rating.

Tornado in WRIGHT, IOWA
From 20-AUG-21 20:05:00 to 20-AUG-21 20:10:00 (CST-6)
Location: GOLDFIELD
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 1.00K
Reported by: Other Federal Agency

Tornado north of Goldfield remained in mostly rural agricultural fields, although some minor tree damage occurred at one farmstead  Path was determined using high resolution satellite imagery.

Heavy Rain in POCAHONTAS, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: POCAHONTAS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 2.15 inches.

Heavy Rain in KOSSUTH, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: ALGONA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 2.54 inches.

Heavy Rain in WRIGHT, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: CLARION
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 3.27 inches.

Heavy Rain in WEBSTER, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: BADGER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 2.37 inches.

Heavy Rain in HAMILTON, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: WEBSTER CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 2.92 inches.

Heavy Rain in GRUNDY, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: CONRAD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 2.50 inches.

Heavy Rain in GRUNDY, IOWA
From 20-AUG-21 07:00:00 to 21-AUG-21 07:00:00 (CST-6)
Location: GRUNDY CENTER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

A 24 hour rain total of 1.93 inches.

Heavy Rain in POCAHONTAS, IOWA
From 20-AUG-21 15:00:00 to 20-AUG-21 18:06:00 (CST-6)
Location: POCAHONTAS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

CWOP report from a personal weather station of 2.41 inches of rain in 3 hours.