A very strong upper level low pressure trough had carved out over the western U.S.  Iowa was in the strong southwest flow on the front side of this system.  A surface warm front lifted north into southwest Iowa during the evening of the 5th.  The airmass became quite unstable with plenty of deep moisture advection into the areas.  Precipitable water values were in the 1.5 to 1.75 inch range by midnight.  The lifted index fell to the -6 to -8 C. There was a reasonable amount of CAPE available with about 2500 J/kg at the onset of the event.  The LCL was around 1000 meters and the freezing level was a relatively high 13,500 feet.  With the warm front in the vicinity, there was a considerable amount of helicity present with values in the 300 to 550 range.  During the evening of the 5th, most of the significant convection remained to the west of the DMX CWA.  After midnight, the low level jet increased to 50 to 70 kts and began to veer.  This helped push the convection east during the overnight hours.  Strong cells developed in southwest Iowa near the warm frontal boundary.  Two tornadoes occurred with this initial set of convection.  An EF2 tornado touched down in Cass County.    The tornado first developed right on the southern Cass County line, from highway 71 to three quarters of a mile west. Four farmsteads were damaged along county road G66 within the mile west of highway 71, producing damage up to EF1.  The tornado narrowed slightly and intensified in the next mile, downing two sets of metal electrical transmission poles. The most severe damage occurred at a farm service and grain elevator business on highway 71.  This was 2 miles into Cass County or 3 miles south of the town of Lyman.  EF2 damage occurred at this site with winds estimated at 120-130 mph.  The average path width was 100 to 200 yards, with a maximum width of about one half mile.  Empty semi trailers were flipped, two tall grain bins were flattened.  A large metal clad truck service building was flattened on the south end and much of the roof was off the north end. The west part of the roof of an office building was torn off and the wall collapsed. The house at the north end of the site had windows blown out and part of the roof damaged.  The tornado continued north along and just east of highway 71 for another two miles causing some damage to homes with some outbuildings unroofed or destroyed.  The last apparent damage along the tornado path occurred two miles northeast of Lyman where power poles were snapped.  Several areas between Cumberland and Anita were also surveyed. Damage along this path was consistent with straight line winds of 70 to 90 mph.  Damage included downed trees and sheet metal torn off sheds and outbuildings.  A storage building in Anita was significantly damaged.  A total of 115 to 120 homes were damaged in Cass County by the storm.  As the night progressed, a bow echo advanced into the state from the southwest.  There were several reports of high winds and hail with this line.  One of the storm in the line produced a small EF0 tornado in Union County.  Some damage occurred at several farmsteads along the path.  This same cell produced very large hail with hail up to baseball size reported in the Afton area.  The hail was wind driven, damaging skylights, windows, and cars.  Hail stones were driven through car windshields and also through windows in houses.  Some damage even occurred inside of two homes as the hail stones continued inside of the house.  This was the most significant hail from the storms.  The hail reportedly piled up several inches deep and lasted for at least 4 hours after the storm.  In the survey conducted by the Emergency Manager it was found that in Afton, 236 primary buildings and 174 out buildings and garages had  moderate hail damage consisting of roof damage...primarily to the slopes facing south and west.  All roof vents and eves, either aluminum or plastic, were damaged. Almost 100 percent of the buildings with south-facing windows had damage to screens, broken glass storm windows, interior single and double pane windows, and in cases of plastic framed windows even the sashes and stools were damaged. All siding was damaged on those sides no matter of the material.  In the rural areas around Afton, 30 of the 38 residences received moderate damage.  In Arispe, 5 miles south of Afton, hail damage occurred, but was not as severe with 40 residences reporting minor damage and 30 out buildings being damaged.  All together, 346 vehicles were hail damaged and many had Windows broken completely out. Twenty three campers suffered vent and sky lite damages as well as exterior damages. Hardly any of the skylights withstood the hail, either in campers or houses.  Though many of the storms produced hail, much of it was under one half inch in diameter.  Another brief tornado touched town in Guthrie County south of Bayard.  The tornado caused EF1 damage.  A roof was blown off of a building there, and blown westward.  Wind was the primary threat with the storms.  There were several reports of trees downed by the high winds, barns, and outbuildings being blown over or destroyed.  A semi-tractortrailer was blown off of Interstate 80 west of Adair.  The event turned into a significant event both in areal coverage, as well as for its variety of weather features.  Flooding became a significant problem later in the event with several reports of 3 to 5 inch rainfall received.  Flash flooding occurred over parts of southwest into west central Iowa.  Cass, Audubon, and Carroll Counties were the hardest hit.  Areal flood warnings were issued for these counties.  Widespread flooding too place, with Cass County hard hit.  The Governor of Iowa, Chet Culver, declared a state disaster for several counties across southwest and south central Iowa due to the flash flooding.  This included Decatur County in the Des Moines CWA.  Toward dawn, high winds became a problem over parts of northwest Iowa.  The winds affected  a 6 county area with wind gusts in the 50 to 65 MPH range for several hours.

High Wind in EMMET, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 56.00 MG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: ASOS

High Wind in HAMILTON, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 52.00 MG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: AWOS

High Wind in PALO ALTO, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 35.00 ES
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

High Wind in POCAHONTAS, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 35.00 ES
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

High Wind in HUMBOLDT, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 35.00 ES
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

High Wind in WEBSTER, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 35.00 MS
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

Tornado in UNION, IOWA
From 06-MAY-07 03:45:00 to 06-MAY-07 03:50:00 (CST-6)
Location: THAYER
Tornado F-scale: EF0
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Tornado formed on the back side of a bow echo.  Damage was limited to EF0, but evidence suggested weak circulation.

High Wind in WRIGHT, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 50.00 MG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

High Wind in KOSSUTH, IOWA
From 06-MAY-07 04:30:00 to 06-MAY-07 11:00:00 (CST-6)
Magnitude: 35.00 ES
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in TAYLOR, IOWA
From 06-MAY-07 02:20:00 to 06-MAY-07 02:30:00 (CST-6)
Location: GRAVITY
Magnitude: 65.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in UNION, IOWA
From 06-MAY-07 03:25:00 to 06-MAY-07 03:25:00 (CST-6)
Location: ARISPE
Magnitude: 2.00 
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Flood in CARROLL, IOWA
From 06-MAY-07 08:45:00 to 06-MAY-07 20:45:00 (CST-6)
Location: LANESBORO
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flood in AUDUBON, IOWA
From 06-MAY-07 08:54:00 to 06-MAY-07 21:00:00 (CST-6)
Location: GRAY
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flood in CASS, IOWA
From 06-MAY-07 09:18:00 to 07-MAY-07 09:15:00 (CST-6)
Location: ANITA
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 0.00K
Reported by: Law Enforcement

Thunderstorm Wind in CASS, IOWA
From 06-MAY-07 02:00:00 to 06-MAY-07 02:00:00 (CST-6)
Location: ANITA
Magnitude: 70.00 EG
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm Wind in ADAIR, IOWA
From 06-MAY-07 02:30:00 to 06-MAY-07 02:30:00 (CST-6)
Location: ADAIR
Magnitude: 57.00 EG
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Newspaper

Thunderstorm Wind in GUTHRIE, IOWA
From 06-MAY-07 02:45:00 to 06-MAY-07 02:45:00 (CST-6)
Location: BAYARD
Magnitude: 70.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Newspaper

Tornado in GUTHRIE, IOWA
From 06-MAY-07 03:37:00 to 06-MAY-07 03:39:00 (CST-6)
Location: BAYARD
Tornado F-scale: EF1
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Tornado was on the ground briefly, but took the roof off of a building and blew it westward.

Flash Flood in CASS, IOWA
From 06-MAY-07 02:42:00 to 06-MAY-07 09:15:00 (CST-6)
Location: ATLANTIC
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Flash Flood in CASS, IOWA
From 06-MAY-07 02:48:00 to 06-MAY-07 09:15:00 (CST-6)
Location: CUMBERLAND
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flash Flood in CASS, IOWA
From 06-MAY-07 02:55:00 to 06-MAY-07 09:15:00 (CST-6)
Location: CUMBERLAND
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Flash Flood in CASS, IOWA
From 06-MAY-07 02:55:00 to 06-MAY-07 09:15:00 (CST-6)
Location: ATLANTIC
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Flash Flood in CASS, IOWA
From 06-MAY-07 03:08:00 to 06-MAY-07 09:15:00 (CST-6)
Location: ATLANTIC
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Flash Flood in CASS, IOWA
From 06-MAY-07 04:15:00 to 06-MAY-07 09:15:00 (CST-6)
Location: GRISWOLD
Flood cause: Heavy Rain
Property damage: 200.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash Flood in AUDUBON, IOWA
From 06-MAY-07 04:20:00 to 06-MAY-07 09:00:00 (CST-6)
Location: AUDUBON
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash Flood in SAC, IOWA
From 06-MAY-07 04:35:00 to 06-MAY-07 08:30:00 (CST-6)
Location: SAC CITY
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash Flood in AUDUBON, IOWA
From 06-MAY-07 05:20:00 to 06-MAY-07 09:00:00 (CST-6)
Location: AUDUBON ARPT
Flood cause: Heavy Rain
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Flash Flood in AUDUBON, IOWA
From 06-MAY-07 05:42:00 to 06-MAY-07 09:00:00 (CST-6)
Location: EXIRA
Flood cause: Heavy Rain
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in CASS, IOWA
From 06-MAY-07 01:54:00 to 06-MAY-07 01:54:00 (CST-6)
Location: FLETCHER CHAPEL
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in UNION, IOWA
From 06-MAY-07 03:20:00 to 06-MAY-07 03:20:00 (CST-6)
Location: AFTON
Magnitude: 1.75 
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Hail in UNION, IOWA
From 06-MAY-07 03:30:00 to 06-MAY-07 03:30:00 (CST-6)
Location: AFTON
Magnitude: 2.75 
Property damage: 750.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Tornado in CASS, IOWA
From 06-MAY-07 01:40:00 to 06-MAY-07 01:49:00 (CST-6)
Location: GRISWOLD
Tornado F-scale: EF2
Property damage: 1.00M
Crop damage: 0.00K
Reported by: NWS Storm Survey

Tornado touched down on the southern Cass County line and moved northeast.  The last 2 miles of the track showed an intermittent nature.  Average path width was 100 to 200 yards wide with a maximum width of about one half mile.  Estimated wind speed was 120 to 130 MPH.

Thunderstorm Wind in ADAIR, IOWA
From 06-MAY-07 03:12:00 to 06-MAY-07 03:12:00 (CST-6)
Location: ADAIR
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in ADAIR, IOWA
From 06-MAY-07 03:17:00 to 06-MAY-07 03:17:00 (CST-6)
Location: BRIDGEWATER
Magnitude: 61.00 EG
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in GUTHRIE, IOWA
From 06-MAY-07 03:25:00 to 06-MAY-07 03:25:00 (CST-6)
Location: NORTH BRANCH
Magnitude: 56.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in GUTHRIE, IOWA
From 06-MAY-07 03:37:00 to 06-MAY-07 03:37:00 (CST-6)
Location: YALE
Magnitude: 70.00 EG
Property damage: 75.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in GUTHRIE, IOWA
From 06-MAY-07 03:50:00 to 06-MAY-07 03:50:00 (CST-6)
Location: JAMAICA
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Employee

Thunderstorm Wind in GUTHRIE, IOWA
From 06-MAY-07 03:53:00 to 06-MAY-07 03:53:00 (CST-6)
Location: JAMAICA
Magnitude: 57.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in WARREN, IOWA
From 06-MAY-07 04:15:00 to 06-MAY-07 04:15:00 (CST-6)
Location: NEW VIRGINIA
Magnitude: 61.00 EG
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in WARREN, IOWA
From 06-MAY-07 04:19:00 to 06-MAY-07 04:19:00 (CST-6)
Location: NEW VIRGINIA
Magnitude: 61.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in ADAMS, IOWA
From 06-MAY-07 02:50:00 to 06-MAY-07 02:50:00 (CST-6)
Location: CORNING
Magnitude: 50.00 EG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: Mesonet