With the help of a couple weak boundaries in the area, storms initiated on the nose of the low level jet and generally remained over the same areas overnight. The primary result of the storms was heavy rainfall, though a few initial storms were able to produce damaging winds and severe hail within 2000+ J/kg CAPE and borderline effective bulk shear around 30 kts.  Other than the few initial severe storm reports, total rainfall reports exceeded 5 inches in some locations.  During the afternoon and evening on the 21st, ahead of a cold front, storms once again initiated and produced primarily sub-severe winds and hail, though two weak tornadoes and one severe wind gust were reported.

Tornado in STORY, IOWA
From 21-AUG-17 16:58:00 to 21-AUG-17 16:59:00 (CST-6)
Location: MIDVALE
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 3.00K
Reported by: NWS Storm Survey

Tornado captured by hi-resolution satellite imagery to the southeast of Ames.  Started just southeast of the water treatment plant and moved quickly through open farm fields with a distinctive path noted in both bean and corn fields.  Little damage noted other than to the crops.

Tornado in BOONE, IOWA
From 21-AUG-17 16:52:00 to 21-AUG-17 16:54:00 (CST-6)
Location: NAPIER
Tornado F-scale: EF0
Property damage: 5.00K
Crop damage: 5.00K
Reported by: NWS Storm Survey

This tornado was found in hi-resolution satellite imagery and crossed mostly open farm fields.  The tornado did damage trees across the corner of one farmstead but otherwise did little other damage.  This tornado continued into Story county.

Tornado in STORY, IOWA
From 21-AUG-17 16:54:00 to 21-AUG-17 16:55:00 (CST-6)
Location: KELLEY
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 4.00K
Reported by: NWS Storm Survey

Tornado found in hi-resolution satellite imagery.  This tornado entered from Boone county and stayed in open row crops, mainly corn where the path was very visible in the imagery.

Heavy Rain in AUDUBON, IOWA
From 20-AUG-17 22:30:00 to 21-AUG-17 08:13:00 (CST-6)
Location: AUDUBON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Local fire department reported heavy rainfall of 5.30 inches.

Heavy Rain in POLK, IOWA
From 20-AUG-17 23:00:00 to 21-AUG-17 15:00:00 (CST-6)
Location: HERROLD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KCCI relayed a viewer report of heavy rainfall of 3.60 inches since midnight.

Thunderstorm Wind in POWESHIEK, IOWA
From 21-AUG-17 18:05:00 to 21-AUG-17 18:05:00 (CST-6)
Location: BROOKLYN
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported estimated 60 to 65 mph winds at Brooklyn exit on I-80.

Heavy Rain in CASS, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: ANITA MUNI ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 2.45 inches over the last 24 hours.

Heavy Rain in AUDUBON, IOWA
From 20-AUG-17 05:55:00 to 21-AUG-17 05:55:00 (CST-6)
Location: AUDUBON ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Audubon AWOS recorded heavy rainfall of 3.17 inches over the last 24 hours.

Heavy Rain in ADAIR, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: ADAIR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 2.40 inches over the last 24 hours.

Heavy Rain in CARROLL, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: MANNING
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 3.37 inches over the last 24 hours.

Heavy Rain in CASS, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: MASSENA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 3.43 inches over the last 24 hours.

Thunderstorm Wind in CASS, IOWA
From 21-AUG-17 01:20:00 to 21-AUG-17 01:20:00 (CST-6)
Location: ATLANTIC
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported three inch tree limbs down and power poles broken.

Flash Flood in AUDUBON, IOWA
From 21-AUG-17 02:15:00 to 21-AUG-17 06:15:00 (CST-6)
Location: AUDUBON
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Law enforcement reported water over the road one half mile south of town from Bluegrass Creek.  Debris and mud remained on the roadway.

Heavy Rain in GUTHRIE, IOWA
From 20-AUG-17 23:15:00 to 21-AUG-17 02:20:00 (CST-6)
Location: GUTHRIE CENTER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 4.30 inches.

Heavy Rain in GUTHRIE, IOWA
From 20-AUG-17 23:15:00 to 21-AUG-17 03:07:00 (CST-6)
Location: GUTHRIE CENTER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported heavy rainfall of 4.70 inches.

Heavy Rain in CRAWFORD, IOWA
From 20-AUG-17 21:40:00 to 21-AUG-17 03:54:00 (CST-6)
Location: DENISON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Online home weather station recorded heavy rainfall of 6.34 inches.

Heavy Rain in CRAWFORD, IOWA
From 20-AUG-17 21:40:00 to 21-AUG-17 03:55:00 (CST-6)
Location: DENISON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Online home weather station measured heavy rainfall of 4.03 inches.

Thunderstorm Wind in CASS, IOWA
From 21-AUG-17 01:05:00 to 21-AUG-17 01:05:00 (CST-6)
Location: ATLANTIC ARPT
Magnitude: 50.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Atlantic Municipal Airport AWOS recorded a 50 kt (58 mph) gust.

Hail in PALO ALTO, IOWA
From 21-AUG-17 01:08:00 to 21-AUG-17 01:08:00 (CST-6)
Location: RUTHVEN
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported quarter sized hail.

Thunderstorm Wind in CASS, IOWA
From 21-AUG-17 01:15:00 to 21-AUG-17 01:15:00 (CST-6)
Location: ATLANTIC
Magnitude: 52.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported several large limbs down and damage to a shed.

Heavy Rain in CRAWFORD, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: DENISON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 6.47 inches over the last 24 hours.

Heavy Rain in CRAWFORD, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: SCHLESWIG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 4.64 inches over the last 24 hours.

Heavy Rain in CASS, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: ATLANTIC
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 2.99 inches over the last 24h ours.

Heavy Rain in DALLAS, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: SHULER MINE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 2.06 inches over the last 24 hours.

Heavy Rain in DALLAS, IOWA
From 20-AUG-17 06:15:00 to 21-AUG-17 06:15:00 (CST-6)
Location: SHULER MINE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 2.28 inches over the last 24 hours.

Heavy Rain in POLK, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: SAYDELL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 2.70 inches over the last 24 hours.

Heavy Rain in SAC, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: WALL LAKE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer reported heavy rainfall of 3.30 inches over the last 24 hours.

Heavy Rain in KOSSUTH, IOWA
From 20-AUG-17 06:00:00 to 21-AUG-17 06:00:00 (CST-6)
Location: SWEA CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 2.93 inches over the last 24 hours.

Heavy Rain in GUTHRIE, IOWA
From 20-AUG-17 07:00:00 to 21-AUG-17 07:00:00 (CST-6)
Location: GUTHRIE CENTER
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer reported heavy rainfall of 4.85 inches over the last 24 hours.

Heavy Rain in POLK, IOWA
From 20-AUG-17 07:01:00 to 21-AUG-17 07:01:00 (CST-6)
Location: LOVINGTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station recorded heavy rainfall of 2.01 inches over the last 24 hours.

Heavy Rain in CASS, IOWA
From 20-AUG-17 07:15:00 to 21-AUG-17 07:15:00 (CST-6)
Location: ATLANTIC
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station recorded heavy rainfall of 2.81 inches over the last 24 hours.

Heavy Rain in POLK, IOWA
From 21-AUG-17 01:00:00 to 21-AUG-17 07:31:00 (CST-6)
Location: DES MOINES
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KCCI recorded 2.20 inches of heavy rainfall overnight.