A strong upper level low pressure system lifted out of the southwest U.S. during the day on the 29th into the overnight hours.  A strong southwest flow aloft was present, with a 115 kt jet in place across the area.  Moisture was limited with the system initially with surface dew points in the low to mid 50s.  The dew point climbed gradually during the afternoon to near 60.  The CAPE was marginal with this system, in the 500 to 1000 J/kg range.  Downdraft CAPE was around 600 J/kg, with available CAPE in the -10 to -30 C layer of the atmosphere between 200 and 300 J/kg.  The freezing level was a relatively low 11,500 feet.  The air mass became unstable during the afternoon and early evening hours as surface temperatures warmed in the upper 70s to low 80s.  The lifted index fell to around -3 C.  Surface low pressure lifted northeast out of Kansas into northeast Kansas by late evening.  A boundary extending north-northeast to south-southwest through the low was the focus for thunderstorm development.  Moisture increased by evening with precipitable water values increasing to 1.1 to 1.3 inches.  A strong line of thunderstorms developed and moved into western Iowa and extended through north central Iowa by evening.  For the most part, the mode of severe weather was in the form of hail.  Numerous reports of nickel to golf ball size hail were received along the line.  Golf ball size hail fell in Cerro Gordo County near Ventura, and also in Greene County northwest of Jamaica.  Most of the storms produced wind gusts of 30 to 50 MPH, though there were spotty reports of 60 MPH winds.

Hail in CERRO GORDO, IOWA
From 29-APR-10 20:12:00 to 29-APR-10 20:12:00 (CST-6)
Location: ROCKWELL
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in CASS, IOWA
From 29-APR-10 19:40:00 to 29-APR-10 19:40:00 (CST-6)
Location: GRISWOLD
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in CASS, IOWA
From 29-APR-10 19:41:00 to 29-APR-10 19:41:00 (CST-6)
Location: GRISWOLD
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Pea size hail combined with the wind.

Hail in HUMBOLDT, IOWA
From 29-APR-10 19:01:00 to 29-APR-10 19:01:00 (CST-6)
Location: THOR
Magnitude: 1.25 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in WORTH, IOWA
From 29-APR-10 18:53:00 to 29-APR-10 18:53:00 (CST-6)
Location: NORTHWOOD
Magnitude: 1.50 
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in WEBSTER, IOWA
From 29-APR-10 18:53:00 to 29-APR-10 18:53:00 (CST-6)
Location: (FOD)FT DODGE MUNI A
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CERRO GORDO, IOWA
From 29-APR-10 18:54:00 to 29-APR-10 18:54:00 (CST-6)
Location: VENTURA
Magnitude: 1.75 
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Public

Hail in WEBSTER, IOWA
From 29-APR-10 18:40:00 to 29-APR-10 18:40:00 (CST-6)
Location: BADGER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CASS, IOWA
From 29-APR-10 19:38:00 to 29-APR-10 19:38:00 (CST-6)
Location: GRISWOLD
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in WEBSTER, IOWA
From 29-APR-10 18:38:00 to 29-APR-10 18:38:00 (CST-6)
Location: (FOD)FT DODGE MUNI A
Magnitude: 1.25 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in WEBSTER, IOWA
From 29-APR-10 18:44:00 to 29-APR-10 18:44:00 (CST-6)
Location: BADGER
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in HUMBOLDT, IOWA
From 29-APR-10 18:47:00 to 29-APR-10 18:47:00 (CST-6)
Location: THOR
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in AUDUBON, IOWA
From 29-APR-10 21:00:00 to 29-APR-10 21:00:00 (CST-6)
Location: IMBALLTON
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in CERRO GORDO, IOWA
From 29-APR-10 19:55:00 to 29-APR-10 19:55:00 (CST-6)
Location: MESERVEY
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CASS, IOWA
From 29-APR-10 19:39:00 to 29-APR-10 19:39:00 (CST-6)
Location: GRISWOLD
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Quarter size hail, combined with 50 MPH winds was reported.

Thunderstorm Wind in HANCOCK, IOWA
From 29-APR-10 19:00:00 to 29-APR-10 19:00:00 (CST-6)
Location: GARNER
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Tree branch damage was reported and a 2 foot diameter tree was blown down.

Hail in GREENE, IOWA
From 29-APR-10 22:42:00 to 29-APR-10 22:42:00 (CST-6)
Location: COOPER
Magnitude: 1.75 
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm Wind in CASS, IOWA
From 29-APR-10 19:38:00 to 29-APR-10 19:38:00 (CST-6)
Location: GRISWOLD
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Nickel size hail also fell with the high winds.

Hail in WEBSTER, IOWA
From 29-APR-10 18:50:00 to 29-APR-10 18:50:00 (CST-6)
Location: GOWRIE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

Thunderstorm Wind in GUTHRIE, IOWA
From 29-APR-10 22:34:00 to 29-APR-10 22:34:00 (CST-6)
Location: BAGLEY
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Wind speeds estimated at 60 MPH.