A cold front moved slowly into Iowa from the northwest as an upper level shortwave lifted northeast across the area.  The atmosphere was marginally unstable with afternoon highs reaching the mid to upper 80s and dewpoint readings in the upper 50s to low 60s.  The lifted index was just 0 to -3 C by early evening.  CAPE was limited to around 1000 J/kg.  With relatively dry air in place, downdraft CAPE was around 1200 J/kg.  CAPE in the -10 to -30 C layer of the atmosphere was between 200 and 400 J/kg, but the freezing level was around 15,000 feet.  There was sufficient shear available with 50 to 55 kts present.  A narrow area of higher precipitable water values moved into the state by evening, with 1.25 to 1.5 inches available.  A line of thunderstorms moved into west central and northwest Iowa during the early evening.  One of the storms produced severe weather with quarter size hail in Sac County.  High winds also occurred with damage from east of Odebolt to Early to Lake View.  Numerous power poles were blown down, roofs were taken from outbuildings including turkey and hog confinements.  Boats were thrown at a dealership.  In the Lake View area, a tree fell and killed a dog.  There were no other injuries.  Prior to the storms moving into Sac County, wind damage was reported in Crawford County in the Ricketts area.  Several trees were blown down.

Thunderstorm Wind in SAC, IOWA
From 23-MAY-12 19:40:00 to 23-MAY-12 19:40:00 (CST-6)
Location: LAKE VIEW
Magnitude: 54.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Measured by weather station. One half mile to my north, a boat dealership reported damage.

Hail in SAC, IOWA
From 23-MAY-12 18:40:00 to 23-MAY-12 18:40:00 (CST-6)
Location: ODEBOLT
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Strong winds also reported.

Hail in SAC, IOWA
From 23-MAY-12 19:30:00 to 23-MAY-12 19:30:00 (CST-6)
Location: WALL LAKE
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in CRAWFORD, IOWA
From 23-MAY-12 18:12:00 to 23-MAY-12 18:12:00 (CST-6)
Location: RICKETTS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in CRAWFORD, IOWA
From 23-MAY-12 18:10:00 to 23-MAY-12 18:10:00 (CST-6)
Location: RICKETTS
Magnitude: 55.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Public

A number of trees in a nearby grove were either downed or lost large limbs.  A gustnado was also observed.  Winds were estimated between 60 and 65 MPH.

Thunderstorm Wind in SAC, IOWA
From 23-MAY-12 19:16:00 to 23-MAY-12 19:30:00 (CST-6)
Location: ODEBOLT
Magnitude: 69.00 EG
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Damage swath observed from east of Odebolt through the Early area, to the east side of Lake View.  Numerous power poles down, roof blown off outbuildings, turkey, and hog confinements buildings, and boats were thrown at a dealership.

Thunderstorm Wind in SAC, IOWA
From 23-MAY-12 19:32:00 to 23-MAY-12 19:32:00 (CST-6)
Location: LAKE VIEW
Magnitude: 78.00 EG
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Public

Thirteen large power poles were snapped along a mile long stretch of Perkins Ave.  One third of the roof of a hog confinement building was ripped off one half mile up the road.  Another half mile up the road, one third of a machine shed was destroyed.  Little damage was noted east or west of this area.  Wind speeds were estimated around 90 MPH.