Warm advection took place over Iowa with a 20 to 25 kt low level jet drawing moisture into the area. Precipitable water values increased to 1.8 inches by mid day.  A shortwave and cold front was approaching from the northwest as the atmosphere became quite unstable.  Lifted indices fell to -9 to -13 C, as CAPE values rose to around 3000 J/kg.  Downdraft CAPE was quite high, in the 1000 to 1300 J/kg range.  The freezing level was quite high, around 15,000 feet.  In spite of that, CAPE in the -10 to -30 C layer of the atmosphere was fairly high at 600 to 1000 J/kg.  The atmosphere was moderately sheared with 35 to 50 kts of shear available.  Thunderstorms first formed in South Dakota during the day.  They moved east, then turned southeast as they became rooted in the boundary layer.  Several supercells formed within the developing MCS as it moved from northeast Nebraska into southwest Iowa.  High winds and large hail were the primary modes of severe weather.  There were several reports of hail one inch or larger in diameter, with baseball size hail reported in Taylor County at Gravity.  High winds caused damage to both property and crops as they gusted to 60 to 75 MPH in several places.  The roof was torn off of a gas station in Taylor County at Bedford.  Trees were snapped off at the base and a two mile wide swath of severe hail damage was reported north and east of town.  High winds stripped the siding off of the north and west side of a house in the Gravity area.

Hail in TAYLOR, IOWA
From 18-AUG-11 17:55:00 to 18-AUG-11 17:55:00 (CST-6)
Location: CONWAY
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 1.00M
Reported by: Trained Spotter

Hail reportedly covering the ground.

Hail in TAYLOR, IOWA
From 18-AUG-11 17:59:00 to 18-AUG-11 17:59:00 (CST-6)
Location: BEDFORD
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 250.00K
Reported by: Trained Spotter

Thunderstorm Wind in TAYLOR, IOWA
From 18-AUG-11 17:34:00 to 18-AUG-11 17:34:00 (CST-6)
Location: NEW MARKET
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Estimated winds of 60 MPH along with penny size hail.

Thunderstorm Wind in TAYLOR, IOWA
From 18-AUG-11 17:40:00 to 18-AUG-11 17:40:00 (CST-6)
Location: GRAVITY
Magnitude: 70.00 EG
Property damage: 150.00K
Crop damage: 100.00K
Reported by: Law Enforcement

Tree limbs up to 12 inches in diameter and power lines were down along a line from Bedford to Gravity.  Extensive tree damage along Highway 2 around Bedford and a roof was blown off of a business in Bedford.  Siding was stripped off of the north and west side of a house there.

Thunderstorm Wind in TAYLOR, IOWA
From 18-AUG-11 20:16:00 to 18-AUG-11 20:16:00 (CST-6)
Location: NEW MARKET
Magnitude: 52.00 EG
Property damage: 3.00K
Crop damage: 250.00K
Reported by: Fire Department/Rescue

Tree limbs were downed by winds estimated of 60 MPH.

Hail in TAYLOR, IOWA
From 18-AUG-11 17:40:00 to 18-AUG-11 17:40:00 (CST-6)
Location: BEDFORD
Magnitude: 2.75 
Property damage: 10.00K
Crop damage: 500.00K
Reported by: Law Enforcement

Hail in TAYLOR, IOWA
From 18-AUG-11 18:06:00 to 18-AUG-11 18:06:00 (CST-6)
Location: BLOCKTON
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in TAYLOR, IOWA
From 18-AUG-11 17:39:00 to 18-AUG-11 17:39:00 (CST-6)
Location: GRAVITY
Magnitude: 2.75 
Property damage: 50.00K
Crop damage: 500.00K
Reported by: Trained Spotter

Baseball size hail reported.

Hail in ADAMS, IOWA
From 18-AUG-11 17:15:00 to 18-AUG-11 17:15:00 (CST-6)
Location: NODAWAY
Magnitude: 1.75 
Property damage: 15.00K
Crop damage: 250.00K
Reported by: Trained Spotter

Hail in TAYLOR, IOWA
From 18-AUG-11 17:40:00 to 18-AUG-11 17:40:00 (CST-6)
Location: GRAVITY
Magnitude: 1.75 
Property damage: 10.00K
Crop damage: 250.00K
Reported by: Fire Department/Rescue