A cold front entered northwest Iowa as low pressure developed over west central Iowa.  A warm front extended east from the low.  The atmosphere was fairly unstable with about 2000 J/kg of CAPE available.  Significant shear was present with 45 to 60 kts of effective shear.  Downdraft CAPE was in the 1200 to 1400 J/lg range.  The freezing level was around 14,000 feet, with 600 J/kg of CAPE in the -10 to -30 C layer of the atmosphere.  Moisture increased during the day with 1.4 inches of precipitable water.  By the evening, the low level jet across the area was over 40 kts.  Thunderstorms fired in the warm air advection area north of the warm front.  The storms became severe with hail the primary mode of severe weather.  Much of the hail was in the nickel to penny size range.  One storm produced hail up to golf ball size in Boone County.  Many of the storms also produced wind gusts of 40 to 50 MPH.  Winds around 60 MPH were reported in Marshall County, damaging trees west of the Laurel area.  High winds also caused tree and shed damage in Calhoun County.

Hail in GREENE, IOWA
From 06-SEP-12 23:06:00 to 06-SEP-12 23:06:00 (CST-6)
Location: CHURDAN
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 5.00K
Reported by: Public

Hail in CALHOUN, IOWA
From 06-SEP-12 22:16:00 to 06-SEP-12 22:16:00 (CST-6)
Location: POMEROY
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 3.00K
Reported by: Trained Spotter

Hail in GREENE, IOWA
From 06-SEP-12 23:04:00 to 06-SEP-12 23:04:00 (CST-6)
Location: CHURDAN
Magnitude: 1.50 
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Public

Some hailstones were possibly larger.

Thunderstorm Wind in CALHOUN, IOWA
From 07-SEP-12 01:00:00 to 07-SEP-12 01:00:00 (CST-6)
Location: POMEROY
Magnitude: 52.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous large tree branches greater than 6 inches in diameter were down.  Loose metal sheeting was observed blowing through the streets.

Thunderstorm Wind in MARSHALL, IOWA
From 07-SEP-12 01:00:00 to 07-SEP-12 01:00:00 (CST-6)
Location: LAUREL
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Public

Two one foot diameter trees were downed along with several large limbs.

Hail in CALHOUN, IOWA
From 06-SEP-12 22:33:00 to 06-SEP-12 22:33:00 (CST-6)
Location: ROCKWELL CITY
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 3.00K
Reported by: Trained Spotter

Hail in CALHOUN, IOWA
From 06-SEP-12 22:25:00 to 06-SEP-12 22:30:00 (CST-6)
Location: SHERWOOD
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Dime to quarter size hail lasted about 5 minutes.

Hail in BOONE, IOWA
From 07-SEP-12 00:22:00 to 07-SEP-12 00:32:00 (CST-6)
Location: BOXHOLM
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Ten minutes of pea to nickel size hail.

Hail in BOONE, IOWA
From 07-SEP-12 00:28:00 to 07-SEP-12 00:28:00 (CST-6)
Location: BOXHOLM
Magnitude: 1.75 
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Emergency Manager reported ping pong to golf ball hail.

Hail in BOONE, IOWA
From 07-SEP-12 00:44:00 to 07-SEP-12 00:44:00 (CST-6)
Location: WOLF
Magnitude: 1.50 
Property damage: 5.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Hail in BOONE, IOWA
From 07-SEP-12 00:50:00 to 07-SEP-12 00:50:00 (CST-6)
Location: BOONE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 3.00K
Reported by: Emergency Manager

Hail in JASPER, IOWA
From 07-SEP-12 02:21:00 to 07-SEP-12 02:21:00 (CST-6)
Location: NEWTON
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Public

Public reported nickel to quarter size hail in downtown Newton.

Hail in BOONE, IOWA
From 07-SEP-12 01:00:00 to 07-SEP-12 01:00:00 (CST-6)
Location: ERICSON
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 5.00K
Reported by: Public

Minor car damage was noted with quarter size hail.

Hail in WEBSTER, IOWA
From 07-SEP-12 02:05:00 to 07-SEP-12 02:05:00 (CST-6)
Location: DAYTON
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 5.00K
Reported by: Public

Hail in JASPER, IOWA
From 07-SEP-12 02:29:00 to 07-SEP-12 02:29:00 (CST-6)
Location: TURNER
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 5.00K
Reported by: Public

Minor car damage was reported.