A cold front pushed into northwest Iowa during the afternoon of the 8th.  Temperatures warmed in to the upper 80s to low 90s, with dewpoint readings in the mid to upper 60s during the afternoon.  CAPE rose to 2000 to 2500 J/kg, though the atmosphere was weakly sheared with 25 kts of shear available.  Downdraft CAPE was significant with around 1000 J/kg available.  The lifted index fell to between -6 to -9 C as moisture increased.  By late afternoon the precipitable water value was around 1.6 inches.  The freezing level was around 13,500 feet, which was not conducive to hail given the weakly sheared environment.  CAPE in the -10 to -30 C layer of the atmosphere was in the 500 to 700 J/kg range.  An area of thunderstorms formed over western Iowa and advanced east across the state.  An area from west central into central Iowa intensified.  Hail up to half dollar size was reported at several locations.  Part of the line began to bow out and was able to take advantage of the DCAPE.  Winds of 60 to 70 MPH moved through central Iowa, including the Des Moines metro area.  Winds near 75 MPH swept into the west side of the Des Moines Metro area.  The winds lasted from 10 to 20 minutes.  Hail falling at the time caused damage to houses as the hail was driven through the siding of some of them.  There were numerous reports of trees down and power outages.  At one point 7,000 to 10,000 customers were out of service.  Heavy rainfall of nearly 2 inches in under an hour was reported around Des Moines.  The heavy rain caused significant street flooding and caused many motorists to stall out.  Thunderstorms formed over northern Iowa during the late afternoon in response to an upper level system.  The storms produced wind gusts as high 66 MPH in the Mason City area.  Quarter size hail was reported from one of the stronger cells in Franklin County.

Hail in POLK, IOWA
From 08-AUG-12 15:04:00 to 08-AUG-12 15:04:00 (CST-6)
Location: URBANDALE
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 15:02:00 to 08-AUG-12 15:02:00 (CST-6)
Location: ASHAWA
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: NWS Employee

Winds estimated in excess of 70 MPH.  Extremely heavy rain as well.

Thunderstorm Wind in CERRO GORDO, IOWA
From 08-AUG-12 16:30:00 to 08-AUG-12 16:30:00 (CST-6)
Location: BURCHINAL
Magnitude: 57.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 15:02:00 to 08-AUG-12 15:02:00 (CST-6)
Location: DES MOINES
Magnitude: 56.00 MG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Hail in POLK, IOWA
From 08-AUG-12 15:04:00 to 08-AUG-12 15:04:00 (CST-6)
Location: RIDER
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 15:09:00 to 08-AUG-12 15:09:00 (CST-6)
Location: LOVINGTON
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Amateur Radio

High winds accompanied by quarter size hail.

Thunderstorm Wind in BOONE, IOWA
From 08-AUG-12 14:25:00 to 08-AUG-12 14:25:00 (CST-6)
Location: BEAVER
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Estimated 60 MPH winds was accompanied by dime size hail.

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 15:11:00 to 08-AUG-12 15:11:00 (CST-6)
Location: CAPITOL HGTS
Magnitude: 56.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Winds in excess of 65 MPH around the State Fair Grounds.

Hail in POLK, IOWA
From 08-AUG-12 15:09:00 to 08-AUG-12 15:09:00 (CST-6)
Location: LOVINGTON
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Heavy Rain in POLK, IOWA
From 08-AUG-12 15:00:00 to 08-AUG-12 16:00:00 (CST-6)
Location: CLOVER HILLS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Rainfall of 1.81 inches in under an hour.

Hail in CARROLL, IOWA
From 08-AUG-12 13:10:00 to 08-AUG-12 13:10:00 (CST-6)
Location: MAPLE RIVER
Magnitude: 1.25 
Property damage: 5.00K
Crop damage: 10.00K
Reported by: SHAVE Project

Heavy Rain in POLK, IOWA
From 08-AUG-12 14:53:00 to 08-AUG-12 15:53:00 (CST-6)
Location: WINDSOR HGTS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Measured 1.69 inches of rain in less than an hour.

Hail in CARROLL, IOWA
From 08-AUG-12 13:27:00 to 08-AUG-12 13:27:00 (CST-6)
Location: MT CARMEL
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: State Official

Thunderstorm Wind in GREENE, IOWA
From 08-AUG-12 14:08:00 to 08-AUG-12 14:08:00 (CST-6)
Location: COOPER
Magnitude: 52.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Numerous trees down in Squirrel Hollow Park.  Some damage to the park bridge with fallen trees.

Hail in CARROLL, IOWA
From 08-AUG-12 13:28:00 to 08-AUG-12 13:28:00 (CST-6)
Location: BREDA
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in FRANKLIN, IOWA
From 08-AUG-12 17:25:00 to 08-AUG-12 17:25:00 (CST-6)
Location: HANSELL
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 14:56:00 to 08-AUG-12 14:56:00 (CST-6)
Location: WINDSOR HGTS
Magnitude: 54.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 15:06:00 to 08-AUG-12 15:06:00 (CST-6)
Location: LOVINGTON
Magnitude: 57.00 MG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in GREENE, IOWA
From 08-AUG-12 13:39:00 to 08-AUG-12 13:39:00 (CST-6)
Location: SCRANTON
Magnitude: 1.00 
Property damage: 1.00K
Crop damage: 5.00K
Reported by: Public

Hail in DALLAS, IOWA
From 08-AUG-12 14:50:00 to 08-AUG-12 14:50:00 (CST-6)
Location: SHULER MINE
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: NWS Employee

An off duty NWS employee reported quarter size hail in Waukee and also relayed that strong winds had blown down tents at the Waukee Farmer's Market. High winds and hail resulted in damaged siding with holes punched through the siding.

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 14:57:00 to 08-AUG-12 14:57:00 (CST-6)
Location: ASHAWA
Magnitude: 52.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous two inch diameter limbs down at the intersection of 68th and Douglas.  Winds in excess of 60 MPH.

Hail in DALLAS, IOWA
From 08-AUG-12 14:37:00 to 08-AUG-12 14:37:00 (CST-6)
Location: DALLAS CENTER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 2.00K
Reported by: Fire Department/Rescue

Only a brief period of hail.

Hail in POLK, IOWA
From 08-AUG-12 15:06:00 to 08-AUG-12 15:06:00 (CST-6)
Location: DES MOINES
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter reported hail up to quarter size along with strong wind gusts.  Multiple branches of 6 to 8 inch diameter were downed.  Minor hail damage to vehicles and standing water in low lying areas, caused by heavy rain.

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 14:55:00 to 08-AUG-12 14:55:00 (CST-6)
Location: CLOVER HILLS
Magnitude: 56.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter estimated winds near 65 MPH.

Thunderstorm Wind in DALLAS, IOWA
From 08-AUG-12 14:54:00 to 08-AUG-12 14:54:00 (CST-6)
Location: HADDEN HILL
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Twelve inch diameter trees were snapped at the base south of the intersection of Hickman and 156th St.

Thunderstorm Wind in POLK, IOWA
From 08-AUG-12 14:55:00 to 08-AUG-12 14:55:00 (CST-6)
Location: URBANDALE
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Four inch diameter tree limbs down in the neighborhood around his residence.