A strong push of moist air occurred during the day on the 1st with surface dewpoint readings climbing to the mid 50s to mid 60s across the state.  The low level jet increased in strength during the evening with wind speeds around 45 kts by mid evening, helping to push precipitable water values to around 1.25 inches.  The atmosphere became unstable with CAPE values in the 2000 to 3000 J/kg range.  Downdraft CAPE was in the 900 J/kg range with a relatively low LCL of 750 meters.  Wind shear, though not strong, was sufficient with 35 to 45 kts of available shear.  The CAPE in the -10 to -30 C layer of the atmosphere was between 200 and 300 J/kg.  The freezing level was around 13,000 feet.  A line of thunderstorms formed ahead of the approaching cold front from South Dakota and moved southeast into Iowa during the mid to late evening hours.  They produced gusty winds and hail as they passed.  The stronger storms produced winds of 60 MPH over northwest into parts of north central and central Iowa, along with hail up to quarter size.  Significant damage occurred in the Ames area as high winds of 70 to 75 MPH moved through Story County.  Large trees were downed in the city.  The garage doors and gutters were damaged on an apartment complex.  A house was significantly damaged as a large tree was blown down onto it.  The strongest winds were estimated to be around 85 MPH due to a microburst.  Around the county, there were numerous reports of tree and outbuilding damage as well.

Thunderstorm Wind in GUTHRIE, IOWA
From 02-MAY-12 00:35:00 to 02-MAY-12 00:35:00 (CST-6)
Location: FANSLERS
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several six inch tree limbs down.

Thunderstorm Wind in MARSHALL, IOWA
From 02-MAY-12 01:19:00 to 02-MAY-12 01:19:00 (CST-6)
Location: STATE CENTER
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several ten inch limbs down.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:59:00 to 02-MAY-12 00:59:00 (CST-6)
Location: ROLAND
Magnitude: 57.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

The top of a tree that was two feet in diameter was snapped off in the town of Roland.

Thunderstorm Wind in CRAWFORD, IOWA
From 01-MAY-12 23:25:00 to 01-MAY-12 23:25:00 (CST-6)
Location: DELOIT
Magnitude: 52.00 EG
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several branches down, a few four inches in diameter.

Thunderstorm Wind in PALO ALTO, IOWA
From 01-MAY-12 21:20:00 to 01-MAY-12 21:20:00 (CST-6)
Location: GRAETTINGER
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Horizontal rain and numerous six inch tree branches down.

Thunderstorm Wind in GRUNDY, IOWA
From 02-MAY-12 01:40:00 to 02-MAY-12 01:40:00 (CST-6)
Location: REINBECK
Magnitude: 57.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large limb toppled a power line which fell across IA 175 in Reinbeck.  Several other large limbs down across the west side of town.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:50:00 to 02-MAY-12 00:50:00 (CST-6)
Location: AMES
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Large trees were uprooted along 13th street in Ames.

Thunderstorm Wind in KOSSUTH, IOWA
From 01-MAY-12 21:55:00 to 01-MAY-12 21:55:00 (CST-6)
Location: WHITTEMORE
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter driving on Highway 15 between Whittemore and Fenton estimated 60 MPH winds and had trouble controlling his car.  Several cars were reported in the ditch with quarter size hail beginning at 2158 CST.

Thunderstorm Wind in WEBSTER, IOWA
From 01-MAY-12 22:34:00 to 01-MAY-12 22:34:00 (CST-6)
Location: (FOD)FT DODGE MUNI A
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Trained spotter reported quarter size hail blowing horizontally against the window.

Thunderstorm Wind in BOONE, IOWA
From 02-MAY-12 00:40:00 to 02-MAY-12 00:50:00 (CST-6)
Location: BOONE
Magnitude: 61.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

The emergency manager reported that four 1 1/2 foot diameter evergreen trees were downed and the roof was torn off of a barn in the northwest corner of Boone.  Also from a mile north of Boone to the eastern border of the county sheeting was strewn about from various buildings.

Thunderstorm Wind in BOONE, IOWA
From 02-MAY-12 00:35:00 to 02-MAY-12 00:40:00 (CST-6)
Location: FRASER
Magnitude: 52.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Several large tree limbs down with damage to fences.  Damage began about a mile south of Fraser and continued sporadically for about 2 miles.

Hail in SAC, IOWA
From 01-MAY-12 22:34:00 to 01-MAY-12 22:34:00 (CST-6)
Location: SAC CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in KOSSUTH, IOWA
From 01-MAY-12 21:58:00 to 01-MAY-12 21:58:00 (CST-6)
Location: WHITTEMORE
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:51:00 to 02-MAY-12 00:51:00 (CST-6)
Location: AMES
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A tree landed on a house and a car in the area of Nixon Circle in Ames.  The tree damaged the gas line to the house.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:50:00 to 02-MAY-12 00:50:00 (CST-6)
Location: AMES
Magnitude: 74.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Damage report within two blocks of Bloomington Rd. and Grand Ave. Shingles off of house roofs, privacy fences down, apartment buildings lost partial balcony, traffic light pole bent over, and trees of one to two foot diameter snapped at bases.

Hail in JASPER, IOWA
From 02-MAY-12 01:58:00 to 02-MAY-12 01:58:00 (CST-6)
Location: PRAIRIE CITY
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:52:00 to 02-MAY-12 00:52:00 (CST-6)
Location: AMES
Magnitude: 53.00 MG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

Wind speed measured at an Ames mesonet site.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:55:00 to 02-MAY-12 00:55:00 (CST-6)
Location: AMES
Magnitude: 63.00 MG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Wind damage reported to trees.  Observer measured wind speed.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:50:00 to 02-MAY-12 00:50:00 (CST-6)
Location: AMES
Magnitude: 74.00 EG
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Garage doors were blown in with gutters torn off of an apartment complex in north Ames.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:52:00 to 02-MAY-12 00:52:00 (CST-6)
Location: AMES ARPT
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A pine tree was uprooted and multiple tree limbs were downed.

Thunderstorm Wind in STORY, IOWA
From 02-MAY-12 00:53:00 to 02-MAY-12 00:53:00 (CST-6)
Location: AMES
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Power lines were reported down in Ames.