A strong push of warm and unstable air pushed north into Iowa during the day on the 6th.  Surface temperatures warmed into the upper 70s to mid 80s across the state, with dew point readings in the 55 to 60 degree range.  A cold front moved into the state from the northwest as an upper level short wave lifted northeast across the state during the evening.  Most unstable CAPE values were in the 1000-2000 J/kg range by the late afternoon.  There was sufficient shear available with the effective shear in the 40 to 50 kt range across the north half of the state.  The LCL was quite high, in the 1250 to 1500 meter range.  Cape in the -10 to -30 C. layer of the atmosphere had around 200 J/kg of CAPE available.  Downdraft CAPE was in the 700 to 900 J/kg range as the soundings indicated an inverted V structure.  The freezing level was around 12,000 feet.  Thunderstorms fired in a broken line extending from the far northwest corner of Iowa, southwest into Nebraska.  The storms became severe quite quickly as they advanced east.  Many of the storms produced hail of around one half inch in diameter or so.  Several produced hail of three quarters of an inch to one inch in diameter.  The hail would have likely been larger if not for the lack of significant CAPE in the -10 to -30 C. layer.  As the line evolved, it became solid from north central into west central Iowa.  Initially, the northern part of the line took on a bow echo configuration and produced high winds across north central into northeast Iowa.  The winds blew over a semi-tractortrailer rig near the 197 mile post on Interstate 35.  The bow echo feature continued east into northeast Iowa.  As the line moved through Bremer County, high winds blew down road signs and caused damage at the Wal-Mart store there.  This feature left an outflow boundary extending east to west across central Iowa.  The boundary provided the focal point for additional thunderstorms, which trained across parts of central into northeast Iowa.  Farther to the west, many of the storms produced hail and some heavy rainfall.  Flooding became a problem with many areas reporting small stream and urban flooding.  Flash flooding, as well as areal flooding, became a problem over Wright and Hardin Counties where 3 to 5 inches of rain fell.  One of the harder hit areas was in Hardin County at Alden where nearly 5 inches of rain was reported in under three hours.  A report of 6.25 inches was received from west of Iowa Falls in Hardin County.  This was over a period of six and one half hours.  Numerous roads were closed in these two counties with water anywhere from 6 to 24 inches deep running across the roads.  In addition, heavy rain fell in the city of Boone in Boone County with water reportedly flowing 6 to 12 inches deep over a number of roads.  There were several road closures in the city of Boone.

Thunderstorm Wind in CERRO GORDO, IOWA
From 06-MAY-08 17:49:00 to 06-MAY-08 17:49:00 (CST-6)
Location: (MCW)MASON CITY MUNI
Magnitude: 57.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in FRANKLIN, IOWA
From 06-MAY-08 18:17:00 to 06-MAY-08 18:17:00 (CST-6)
Location: LATIMER
Magnitude: 53.00 MG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in BREMER, IOWA
From 06-MAY-08 19:30:00 to 06-MAY-08 19:30:00 (CST-6)
Location: WAVERLY
Magnitude: 57.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: NWS Employee

Flash Flood in BOONE, IOWA
From 06-MAY-08 20:14:00 to 06-MAY-08 23:00:00 (CST-6)
Location: SHELDAHL
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Six inches to one foot of water running over roads resulted in a number of road closures in Boone County.

Flood in HARDIN, IOWA
From 07-MAY-08 05:28:00 to 07-MAY-08 10:17:00 (CST-6)
Location: IOWA FALLS
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

The Hardin County Sheriff reported the intersection of D15 and D20 closed between Iowa Falls and Alden.

Hail in EMMET, IOWA
From 06-MAY-08 15:47:00 to 06-MAY-08 15:47:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail reportedly covered the ground.

Hail in EMMET, IOWA
From 06-MAY-08 15:52:00 to 06-MAY-08 15:52:00 (CST-6)
Location: GRUVER
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in EMMET, IOWA
From 06-MAY-08 15:58:00 to 06-MAY-08 15:58:00 (CST-6)
Location: ARMSTRONG
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in KOSSUTH, IOWA
From 06-MAY-08 16:17:00 to 06-MAY-08 16:17:00 (CST-6)
Location: LOTTS CREEK
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SAC, IOWA
From 06-MAY-08 17:17:00 to 06-MAY-08 17:17:00 (CST-6)
Location: SAC CITY
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: County Official

Hail reported to be dime to quarter size.

Hail in SAC, IOWA
From 06-MAY-08 17:19:00 to 06-MAY-08 17:19:00 (CST-6)
Location: SAC CITY
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in SAC, IOWA
From 06-MAY-08 17:20:00 to 06-MAY-08 17:20:00 (CST-6)
Location: SAC CITY
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Two periods of hail occurred with the first lasting 30 to 45 seconds, the second was 2 minutes later and lasted 3-5 minutes.  Hail covered the ground with half to three quarter inch hail.

Hail in CALHOUN, IOWA
From 06-MAY-08 17:24:00 to 06-MAY-08 17:24:00 (CST-6)
Location: JOLLEY
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in CALHOUN, IOWA
From 06-MAY-08 17:35:00 to 06-MAY-08 17:35:00 (CST-6)
Location: SHERWOOD
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Hail in SAC, IOWA
From 06-MAY-08 17:45:00 to 06-MAY-08 17:45:00 (CST-6)
Location: SAC CITY
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in CALHOUN, IOWA
From 06-MAY-08 17:54:00 to 06-MAY-08 17:54:00 (CST-6)
Location: SOMERS
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in HAMILTON, IOWA
From 06-MAY-08 18:51:00 to 06-MAY-08 18:51:00 (CST-6)
Location: JEWELL
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Hail in BOONE, IOWA
From 06-MAY-08 19:29:00 to 06-MAY-08 19:29:00 (CST-6)
Location: BOONE
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy Rain in WINNEBAGO, IOWA
From 06-MAY-08 17:05:00 to 06-MAY-08 17:20:00 (CST-6)
Location: RAKE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

One half inch of rain fell in 15 minutes.

Heavy Rain in BLACK HAWK, IOWA
From 06-MAY-08 19:53:00 to 06-MAY-08 20:08:00 (CST-6)
Location: DEWAR
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

One half inch of rain fell in 15 minutes.

Heavy Rain in STORY, IOWA
From 06-MAY-08 19:42:00 to 06-MAY-08 20:42:00 (CST-6)
Location: AMES
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A trained spotter reported 1.6 inches of rain in the past hour.

Heavy Rain in BOONE, IOWA
From 06-MAY-08 19:18:00 to 06-MAY-08 20:48:00 (CST-6)
Location: BOONE
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rain of 3 inches caused basement flooding in Boone.

Heavy Rain in STORY, IOWA
From 06-MAY-08 20:00:00 to 06-MAY-08 21:28:00 (CST-6)
Location: ONTARIO
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Rainfall of 2.73 inches was measured in Ames during the past hour and one half.

Heavy Rain in HARDIN, IOWA
From 06-MAY-08 18:45:00 to 07-MAY-08 01:15:00 (CST-6)
Location: IOWA FALLS
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

The rain began around 1845 CST Tuesday evening and ended around 0115 CST Wednesday morning.  A total of 6.25 inches was reported.

Thunderstorm Wind in CERRO GORDO, IOWA
From 06-MAY-08 17:48:00 to 06-MAY-08 17:48:00 (CST-6)
Location: (MCW)MASON CITY MUNI
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A semi-tractortrailer truck was blown over near mile post 197 on Interstate 35.

Thunderstorm Wind in FRANKLIN, IOWA
From 06-MAY-08 18:40:00 to 06-MAY-08 18:40:00 (CST-6)
Location: GENEVA
Magnitude: 52.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Six inch tree limbs were blown down on the highway.

Thunderstorm Wind in FRANKLIN, IOWA
From 06-MAY-08 18:45:00 to 06-MAY-08 18:45:00 (CST-6)
Location: GENEVA
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Large trees were blown down by 60 MPH winds.

Flash Flood in WRIGHT, IOWA
From 06-MAY-08 23:30:00 to 07-MAY-08 02:00:00 (CST-6)
Location: CLARION ARPT
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A portion of County Road R38 had water over the road near the intersection of R38 and 280th St.  There were also reports of water over County Road C54.  Flooding was also reported near the intersection of 290th and Madison, and also at 200th and Calhoun.

Flash Flood in HARDIN, IOWA
From 06-MAY-08 23:34:00 to 07-MAY-08 02:00:00 (CST-6)
Location: IOWA FALLS MUNI ARPT
Flood cause: Heavy Rain
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Twelve inches of water was flowing over County Road D20, or old Highway 20, at the 18,000 block.

Flood in HARDIN, IOWA
From 07-MAY-08 01:30:00 to 07-MAY-08 10:17:00 (CST-6)
Location: IOWA FALLS
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 0.00K
Reported by: County Official

The Mayor of Alden reported that the Alden Elementary School was closed Wednesday due to 4 feet of water in the boiler room and a foot of water in the cafeteria.  The water softener, main compressor, and several chemicals have water damage in the boiler room as well.

Flood in HARDIN, IOWA
From 07-MAY-08 05:36:00 to 07-MAY-08 10:17:00 (CST-6)
Location: IOWA FALLS
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: County Official

The Mayor of Alden reported that several County Roads were washed out or covered with water in and around Alden.  The Alden Fire Department was pumping water out of drains due to storm drains running full and manhole covers popping.

Hail in PALO ALTO, IOWA
From 06-MAY-08 16:01:00 to 06-MAY-08 16:01:00 (CST-6)
Location: RUTHVEN
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in SAC, IOWA
From 06-MAY-08 17:10:00 to 06-MAY-08 17:10:00 (CST-6)
Location: SAC CITY
Magnitude: 1.00 
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Law Enforcement