The cold front that progressed into the state during the evening of the 23rd made little progress overnight.  It moved slowly southeast during the day on the 24th and finally passed southeast of the CWA after a surface wave lifted northeast along the front.  The airmass was capped initially with the cap finally breaking during the mid afternoon hours.  A narrow line of thunderstorms formed by mid afternoon and advanced across the state.  There was plenty of moisture available with dewpoint readings in the low to mid 60s in a ribbon ahead of the front.  Precipitable water values increased to 1.3 to 1.5 inches.  Shear was strong with 60 to 75 kts of shear available.  The mean flow in the 850-300 mb layer was over 60 kts.  Downdraft CAPE remained quite high with 800 to 1300 J/kg available ahead of the line.  CAPE in the -10 to -30 C layer of the atmosphere was between 300 and 500 J/kg, though the freezing level remained in the 14,000 to 15,000 foot range, limiting hail production.  The LCL was also relatively high in the 750 to 1250 meter range ahead of the line.  Lifted indices fell to -3 to -5 C by late afternoon.  The thunderstorms produced brief heavy rainfall and gusty winds in most locations with storm forward motion speeds in the 50-60 MPH range.  Winds gusted up to 70 MPH with a few of the stronger storms causing damage to trees and power lines.  A storm in Decatur County dropped 1.10 inches of rain in about 20 minutes.  There were spotty reports of three quarter to one inch diameter hail as well.

Hail in BUTLER, IOWA
From 24-MAY-12 15:05:00 to 24-MAY-12 15:05:00 (CST-6)
Location: NEW ALBION
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in FRANKLIN, IOWA
From 24-MAY-12 14:55:00 to 24-MAY-12 14:55:00 (CST-6)
Location: FAULKNER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SHAVE Project

Hail in DECATUR, IOWA
From 24-MAY-12 15:30:00 to 24-MAY-12 15:30:00 (CST-6)
Location: LAMONI
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 24-MAY-12 15:10:00 to 24-MAY-12 15:10:00 (CST-6)
Location: PARKERSBURG
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: SHAVE Project

Thunderstorm Wind in BREMER, IOWA
From 24-MAY-12 15:44:00 to 24-MAY-12 15:44:00 (CST-6)
Location: SUMNER
Magnitude: 57.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Numerous large trees downed by high winds.

Thunderstorm Wind in BLACK HAWK, IOWA
From 24-MAY-12 16:25:00 to 24-MAY-12 16:25:00 (CST-6)
Location: EVANSDALE
Magnitude: 61.00 MG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Mesonet

Hail in BLACK HAWK, IOWA
From 24-MAY-12 16:33:00 to 24-MAY-12 16:33:00 (CST-6)
Location: DUNKERTON
Magnitude: 1.00 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Strong winds also damaged a new swing set.

Thunderstorm Wind in BLACK HAWK, IOWA
From 24-MAY-12 16:20:00 to 24-MAY-12 16:20:00 (CST-6)
Location: ORANGE
Magnitude: 57.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Three foot diameter tree at Orange Elementary School was uprooted.  Numerous large tree branches were downed near the school along Washington Street.

Hail in BUTLER, IOWA
From 24-MAY-12 14:50:00 to 24-MAY-12 14:50:00 (CST-6)
Location: DUMONT
Magnitude: 1.00 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in DECATUR, IOWA
From 24-MAY-12 15:50:00 to 24-MAY-12 15:50:00 (CST-6)
Location: DAVIS CITY
Magnitude: 1.00 
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Also 1.10 inches of rain in 20 minutes.