A surge of moisture streamed north toward Iowa during the afternoon of the 13th.  The moisture interacted with a stalled frontal boundary extending nearly east to west across southern Iowa.  CAPE values were in the 1000 to 3000 J/kg range just southwest of the front, with lifted indices of -5 to -8 C.  The shear was sufficient at 40 to 50 kts.  There was limited CAPE available in the -10 to -30 C layer of the atmosphere with 200 to 700 J/kg available.  The downdraft CAPE was between 600 and 900 J/kg.  The LCL was quite high over Iowa, near 2000 meters.  Precipitable water values increased from around .5 inches in the morning to between 1 and 1.5 inches by late afternoon.  The freezing level was between 12,000 and 13,000 feet.  Thunderstorms formed over eastern Nebraska and advanced into western Iowa during the early afternoon hours.  The storms produced penny to quarter size hail and wind gusts of 60 to 65 MPH in Crawford County.  Quarter size hail also fell in from the same cluster of storms as they moved across Guthrie County.  The storms continued to move east and eventually formed a line of intense storms from west central into southeast Iowa.  They produced nickle size hail and gusty winds, however the heavy rain was more significant with the storms.   A band of 1 to 3 inch rainfall occurred from south of Atlantic through Centerville.  Isolated 4 inch amounts occurred within this 25 mile wide band.  In Appanoose County, flash flooding washed out a significant gravel road south of Centerville.

Heavy Rain in CASS, IOWA
From 13-SEP-10 14:49:00 to 13-SEP-10 16:49:00 (CST-6)
Location: GRISWOLD
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A spotter reported 2.64 inches of rain in the past 2 hours, along with pea size hail.

Hail in GUTHRIE, IOWA
From 13-SEP-10 14:46:00 to 13-SEP-10 14:46:00 (CST-6)
Location: GUTHRIE CENTER
Magnitude: 0.88 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Public

Nickel size hail reported at a gas station in Guthrie Center.

Hail in GUTHRIE, IOWA
From 13-SEP-10 14:47:00 to 13-SEP-10 14:47:00 (CST-6)
Location: GUTHRIE CENTER
Magnitude: 1.00 
Property damage: 2.00K
Crop damage: 10.00K
Reported by: Public

Quarter size hail and heavy rain reported.

Hail in WAYNE, IOWA
From 13-SEP-10 17:20:00 to 13-SEP-10 17:20:00 (CST-6)
Location: HUMESTON
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 5.00K
Reported by: Public

Flash Flood in APPANOOSE, IOWA
From 13-SEP-10 20:00:00 to 13-SEP-10 22:23:00 (CST-6)
Location: CINCINNATI
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 5.00K
Reported by: Public

Significant gravel road washout south of Centerville.

Hail in GUTHRIE, IOWA
From 13-SEP-10 14:45:00 to 13-SEP-10 14:45:00 (CST-6)
Location: MONTEITH
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 10.00K
Reported by: Public

Hail in GUTHRIE, IOWA
From 13-SEP-10 15:05:00 to 13-SEP-10 15:05:00 (CST-6)
Location: DALE
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in CRAWFORD, IOWA
From 13-SEP-10 13:33:00 to 13-SEP-10 13:33:00 (CST-6)
Location: DOW CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in CRAWFORD, IOWA
From 13-SEP-10 13:37:00 to 13-SEP-10 13:37:00 (CST-6)
Location: DOW CITY
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 15.00K
Reported by: Post Office

Dime to quarter size hail was partially covering the ground.

Thunderstorm Wind in CRAWFORD, IOWA
From 13-SEP-10 13:57:00 to 13-SEP-10 13:57:00 (CST-6)
Location: DENISON
Magnitude: 55.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Hail in GUTHRIE, IOWA
From 13-SEP-10 14:48:00 to 13-SEP-10 14:48:00 (CST-6)
Location: GUTHRIE CENTER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Trained Spotter