A predominantly stalled out east-west oriented surface boundary found itself situated across southern Iowa on the 11th and drifted slowly into northern Iowa by the 12th.  Given the boundary location, storms that initiated were elevated in nature and predominantly limited to a hail and heavy rain threat.  The convective environment contained MUCAPE values throughout this time frame in the 1000-2000 J/kg range coincident with roughly 30-40 kts of effective bulk shear.  Generally, convection was initiated with the aide of  the low level jet, leading to relatively widespread multi-cellular clusters versus discrete cells.  In all, severe hail was difficult to come by, while heavy rainfall was more prevalent in the 1.5 to 2.5 inch range.

Hail in WARREN, IOWA
From 12-MAY-18 02:35:00 to 12-MAY-18 02:35:00 (CST-6)
Location: ST MARYS
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported quarter sized hail. Time was estimated from radar.

Hail in GUTHRIE, IOWA
From 12-MAY-18 01:04:00 to 12-MAY-18 01:04:00 (CST-6)
Location: STUART
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public reported quarter size hail.  Time was estimated from radar.

Heavy Rain in MADISON, IOWA
From 11-MAY-18 05:27:00 to 12-MAY-18 05:27:00 (CST-6)
Location: EARLHAM
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded 1.55 inches of heavy rainfall over the last 24 hours.

Heavy Rain in POLK, IOWA
From 11-MAY-18 06:00:00 to 12-MAY-18 06:00:00 (CST-6)
Location: ORALABOR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 1.71 inches over the last 24 hours.

Heavy Rain in POLK, IOWA
From 11-MAY-18 06:00:00 to 12-MAY-18 06:00:00 (CST-6)
Location: POLK CITY
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Official NWS Observations

NWS office recorded heavy rainfall of 1.72 inches over the last 24 hours, including 1.45 inches since 1 am.

Heavy Rain in TAYLOR, IOWA
From 11-MAY-18 06:30:00 to 12-MAY-18 06:30:00 (CST-6)
Location: GUSS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRaHS observer recorded heavy rainfall of 1.48 inches over the last 24 hours.

Heavy Rain in MAHASKA, IOWA
From 12-MAY-18 01:30:00 to 12-MAY-18 08:00:00 (CST-6)
Location: OSKALOOSA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Social Media

Public measured 1.8 inches of heavy rainfall for the event through about 9am.

Heavy Rain in RINGGOLD, IOWA
From 12-MAY-18 05:15:00 to 12-MAY-18 08:15:00 (CST-6)
Location: KELLERTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter measured heavy rainfall of 1.9 inches from about 6 am through 9:15 am this morning.

Heavy Rain in DALLAS, IOWA
From 12-MAY-18 00:45:00 to 12-MAY-18 08:45:00 (CST-6)
Location: HADDEN HILL
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter measured 1.49 inches of heavy rainfall from about 1:45 am to 9:45 am.

Heavy Rain in POWESHIEK, IOWA
From 12-MAY-18 05:55:00 to 13-MAY-18 05:55:00 (CST-6)
Location: GRINNELL ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: AWOS

Grinnell Airport AWOS station recorded heavy rainfall of 2.22 inches over the last 24 hours.

Heavy Rain in JASPER, IOWA
From 12-MAY-18 06:00:00 to 13-MAY-18 06:00:00 (CST-6)
Location: NEWTON
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 1.42 inches over the last 24 hours.

Heavy Rain in POWESHIEK, IOWA
From 12-MAY-18 06:00:00 to 13-MAY-18 06:00:00 (CST-6)
Location: GRINNELL ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 2.12 inches over the last 24 hours.

Heavy Rain in POWESHIEK, IOWA
From 12-MAY-18 06:00:00 to 13-MAY-18 06:00:00 (CST-6)
Location: BROOKLYN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Coop observer recorded heavy rainfall of 2.08 inches over the last 24 hours.