A weak, relatively stationary boundary, was situated from west to east across Iowa throughout the day.  Surface conditions reached a balmy mid to upper 90s south of the boundary with dew points well into the 70s, while north of the boundary conditions were not much better with dew points in the 70s and temperatures in the upper 80s to low 90s.  The convective environment resulted in MUCAPE values exceeding 5000 J/kg across southern Iowa and at least 2000 J/kg available across far northern Iowa.  Best effective shear values were located near and north of the boundary where 30 to 40 kts existed.  Storms initially developed in Nebraska and propagated near/along the boundary eastward into Iowa.  The primary results were damaging winds and borderline hail.  In a few instances, storms initiated ahead of the main batch, allowing for some locations to experience extended periods of heavy rainfall to the tune of 2 to nearly 4 inches.

Thunderstorm Wind in CRAWFORD, IOWA
From 20-JUL-17 18:05:00 to 20-JUL-17 18:05:00 (CST-6)
Location: KIRON
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter estimated wind gusts to 60 mph and reported tree branches down.

Thunderstorm Wind in CRAWFORD, IOWA
From 20-JUL-17 18:12:00 to 20-JUL-17 18:12:00 (CST-6)
Location: KIRON
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported corn flattened and small to mid-size tree branches down.  Time radar estimated.

Hail in GUTHRIE, IOWA
From 20-JUL-17 18:20:00 to 20-JUL-17 18:20:00 (CST-6)
Location: BAYARD
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Local fire department reported nickel sized hail.

Thunderstorm Wind in SAC, IOWA
From 20-JUL-17 18:17:00 to 20-JUL-17 18:17:00 (CST-6)
Location: WALL LAKE
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Delayed report from Wall Lake post office of large tree down near Needham Ave.  Time estimated from radar.

Thunderstorm Wind in CARROLL, IOWA
From 20-JUL-17 19:01:00 to 20-JUL-17 19:01:00 (CST-6)
Location: CARROLL NEU ARPT
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported wind gusts to around 60 mph along with some small branches down as well.

Thunderstorm Wind in BOONE, IOWA
From 20-JUL-17 20:27:00 to 20-JUL-17 20:27:00 (CST-6)
Location: MADRID
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported wind gusts to around 60 mph along with small branches down.

Thunderstorm Wind in DALLAS, IOWA
From 20-JUL-17 20:01:00 to 20-JUL-17 20:01:00 (CST-6)
Location: DAWSON
Magnitude: 51.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported 59 mph wind gust.

Thunderstorm Wind in DALLAS, IOWA
From 20-JUL-17 20:13:00 to 20-JUL-17 20:13:00 (CST-6)
Location: MINBURN
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Local fire department reported wind gusts to 60 mph.

Thunderstorm Wind in DALLAS, IOWA
From 20-JUL-17 20:08:00 to 20-JUL-17 20:08:00 (CST-6)
Location: PERRY
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Perry polic reported trees down in town.  This is a delayed report and time estimated from radar.

Thunderstorm Wind in DALLAS, IOWA
From 20-JUL-17 21:00:00 to 20-JUL-17 21:00:00 (CST-6)
Location: PERRY MUNI ARPT
Magnitude: 56.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Dallas County Sheriff reported to Iowa DOT a tree down on Highway 141 at mile marker 127.  This is a delayed report and time estimated from radar.

Heavy Rain in STORY, IOWA
From 20-JUL-17 19:45:00 to 20-JUL-17 21:12:00 (CST-6)
Location: AMES
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported heavy rainfall of 2.47 inches in north Ames.

Thunderstorm Wind in GUTHRIE, IOWA
From 20-JUL-17 20:00:00 to 20-JUL-17 20:05:00 (CST-6)
Location: JAMAICA
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The emergency manager reported a large 2 foot diameter tree down in Yale and several large branches down in Jamaica. One large branch fell on a truck with minor damage.

Hail in GUTHRIE, IOWA
From 20-JUL-17 18:30:00 to 20-JUL-17 18:30:00 (CST-6)
Location: BAYARD
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Local fire department reported quarter size hail that started around 7 pm.

Heavy Rain in CRAWFORD, IOWA
From 20-JUL-17 17:00:00 to 20-JUL-17 18:39:00 (CST-6)
Location: DENISON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported heavy rainfall of 2.12 inches from 6pm to the report time.

Heavy Rain in DALLAS, IOWA
From 20-JUL-17 19:00:00 to 20-JUL-17 20:26:00 (CST-6)
Location: DAWSON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported heavy rainfall of 3.84 inches form this evening.

Thunderstorm Wind in BOONE, IOWA
From 20-JUL-17 20:20:00 to 20-JUL-17 20:20:00 (CST-6)
Location: BOXHOLM
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A large tree was downed in a yard.

Thunderstorm Wind in GUTHRIE, IOWA
From 20-JUL-17 19:37:00 to 20-JUL-17 19:37:00 (CST-6)
Location: BAGLEY
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Local fire department reported 2 to 3 foot diameter tree down in Bagley.  Time estimated from radar.

Thunderstorm Wind in BOONE, IOWA
From 20-JUL-17 20:32:00 to 20-JUL-17 20:32:00 (CST-6)
Location: MADRID
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Emergency manager reported numerous small branches broken or down.  Time estimated from radar.