A very unstable airmass, typical of July, was in place over Iowa.  Afternoon temperatures warmed into the upper 80s to low 90s, with dew point temperatures in the upper 60s to low 70s.  By the mid and late afternoon hours, lifted indices were in the -8 to -10 C. range and CAPE was between 4000 and 5000 J/kg.  The airmass was quite warm with freezing levels in the 13,000 to 15,000 foot range.  The best shear was over the east third of the state, where values were close to 40 kts of effective shear.  The values tapered off to around 25 kts over the west third.  There was plenty of CAPE available in the -10 to -30 C. level of the atmosphere with values in the 400 to 500 J/kg range.  LCL levels ranged from around 1000 meters over eastern Iowa, to around 1500 meters over the west.  A weak surface low pressure was located over central South Dakota during the afternoon.  A stationary front extended from the low, east-southeast into the northeast corner of Iowa.  Initial development took place over eastern South Dakota, with secondary development over eastern Iowa.  The area over South Dakota tracked southeast into northwest and north central Iowa, while the development over eastern Iowa tracked slowly south.  Initially, the thunderstorms over the northwest produced winds of 60 to 70 MPH, with one report of 80 MPH winds.  In the Armstrong area, 70 to 80 MPH winds rendered roadways impassible and tore gutters off of houses.  The area over the east produced mainly hail and heavy rain.  Hail up to softball size occurred in the Cedar Falls area, with baseball size hail in Black Hawk County near Waterloo.  As the evening progressed, the convection to the northwest became more organized as it reached the convection to the east.  A large supercell formed over Grundy County.  It has a pronounced anti-cyclonic circulation with it as it tracked southeast into northern Tama County.  There were several reports of funnel clouds all the way from Worth County southeast to Tama County.  It turned out that many of the reports were of gustnadoes, forming on the east edge of the line along the outflow boundary.  They lacked depth and no reports of damage were received.

Hail in BUTLER, IOWA
From 16-JUL-07 16:45:00 to 16-JUL-07 16:45:00 (CST-6)
Location: PACKARD
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 16-JUL-07 16:52:00 to 16-JUL-07 16:52:00 (CST-6)
Location: PACKARD
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 16-JUL-07 17:24:00 to 16-JUL-07 17:24:00 (CST-6)
Location: CLARKSVILLE
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 16-JUL-07 17:30:00 to 16-JUL-07 17:30:00 (CST-6)
Location: CLARKSVILLE
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 16-JUL-07 17:42:00 to 16-JUL-07 17:42:00 (CST-6)
Location: SHELL ROCK
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 17:54:00 to 16-JUL-07 17:54:00 (CST-6)
Location: FINCHFORD
Magnitude: 2.00 
Property damage: 35.00K
Crop damage: 10.00K
Reported by: Public

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:20:00 to 16-JUL-07 16:20:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:22:00 to 16-JUL-07 16:22:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 2.00K
Reported by: Trained Spotter

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:28:00 to 16-JUL-07 16:28:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 65.00 EG
Property damage: 50.00K
Crop damage: 5.00K
Reported by: Law Enforcement

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:20:00 to 16-JUL-07 16:20:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 61.00 EG
Property damage: 10.00K
Crop damage: 2.00K
Reported by: Emergency Manager

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:40:00 to 16-JUL-07 16:40:00 (CST-6)
Location: ARMSTRONG
Magnitude: 65.00 EG
Property damage: 75.00K
Crop damage: 20.00K
Reported by: Trained Spotter

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 16:55:00 to 16-JUL-07 16:55:00 (CST-6)
Location: SWEA CITY
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 16:55:00 to 16-JUL-07 16:55:00 (CST-6)
Location: SWEA CITY
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:20:00 to 16-JUL-07 16:20:00 (CST-6)
Location: ESTHERVILLE
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Thunderstorm Wind in HANCOCK, IOWA
From 16-JUL-07 17:45:00 to 16-JUL-07 17:45:00 (CST-6)
Location: GARNER
Magnitude: 57.00 EG
Property damage: 25.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in HANCOCK, IOWA
From 16-JUL-07 17:47:00 to 16-JUL-07 17:47:00 (CST-6)
Location: GARNER
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:30:00 to 16-JUL-07 18:30:00 (CST-6)
Location: CEDAR FALLS ARPT
Magnitude: 1.75 
Property damage: 10.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:30:00 to 16-JUL-07 18:30:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.75 
Property damage: 20.00K
Crop damage: 10.00K
Reported by: Emergency Manager

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:30:00 to 16-JUL-07 18:30:00 (CST-6)
Location: HUDSON
Magnitude: 4.25 
Property damage: 50.00K
Crop damage: 25.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 19:20:00 to 16-JUL-07 19:21:00 (CST-6)
Location: LA PORTE CITY
Magnitude: 0.88 
Property damage: 3.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 16:55:00 to 16-JUL-07 16:55:00 (CST-6)
Location: SENECA
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 17:15:00 to 16-JUL-07 17:15:00 (CST-6)
Location: SEXTON
Magnitude: 57.00 EG
Property damage: 10.00K
Crop damage: 25.00K
Reported by: Emergency Manager

Thunderstorm Wind in HANCOCK, IOWA
From 16-JUL-07 17:52:00 to 16-JUL-07 17:52:00 (CST-6)
Location: BRITT
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorm Wind in CERRO GORDO, IOWA
From 16-JUL-07 18:19:00 to 16-JUL-07 18:19:00 (CST-6)
Location: MASON CITY
Magnitude: 51.00 MG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Mesonet

Thunderstorm Wind in CERRO GORDO, IOWA
From 16-JUL-07 18:20:00 to 16-JUL-07 18:20:00 (CST-6)
Location: MASON CITY
Magnitude: 50.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorm Wind in FRANKLIN, IOWA
From 16-JUL-07 18:35:00 to 16-JUL-07 18:35:00 (CST-6)
Location: HAMPTON
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Public

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:00:00 to 16-JUL-07 18:00:00 (CST-6)
Location: FINCHFORD
Magnitude: 2.75 
Property damage: 50.00K
Crop damage: 20.00K
Reported by: Public

Hail in BUTLER, IOWA
From 16-JUL-07 18:06:00 to 16-JUL-07 18:06:00 (CST-6)
Location: NEW HARTFORD
Magnitude: 1.75 
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:09:00 to 16-JUL-07 18:09:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 2.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:10:00 to 16-JUL-07 18:10:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.00 
Property damage: 10.00K
Crop damage: 2.00K
Reported by: Trained Spotter

Hail in BUTLER, IOWA
From 16-JUL-07 18:10:00 to 16-JUL-07 18:10:00 (CST-6)
Location: FARMER
Magnitude: 2.75 
Property damage: 35.00K
Crop damage: 10.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:12:00 to 16-JUL-07 18:12:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.00 
Property damage: 20.00K
Crop damage: 5.00K
Reported by: Public

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:12:00 to 16-JUL-07 18:12:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.00 
Property damage: 20.00K
Crop damage: 5.00K
Reported by: Public

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:13:00 to 16-JUL-07 18:13:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 2.50 
Property damage: 35.00K
Crop damage: 20.00K
Reported by: Public

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:15:00 to 16-JUL-07 18:15:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 2.75 
Property damage: 200.00K
Crop damage: 5.00K
Reported by: Public

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:17:00 to 16-JUL-07 18:17:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.50 
Property damage: 25.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:27:00 to 16-JUL-07 18:27:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 1.00 
Property damage: 5.00K
Crop damage: 5.00K
Reported by: Broadcast Media

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 16:50:00 to 16-JUL-07 17:15:00 (CST-6)
Location: SWEA CITY
Magnitude: 52.00 EG
Property damage: 15.00K
Crop damage: 5.00K
Reported by: Trained Spotter

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:32:00 to 16-JUL-07 16:32:00 (CST-6)
Location: ESTHERVILLE ARPT
Magnitude: 54.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:38:00 to 16-JUL-07 16:38:00 (CST-6)
Location: ESTHERVILLE ARPT
Magnitude: 56.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: ASOS

Thunderstorm Wind in KOSSUTH, IOWA
From 16-JUL-07 16:45:00 to 16-JUL-07 17:15:00 (CST-6)
Location: BANCROFT
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 100.00K
Reported by: Newspaper

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:35:00 to 16-JUL-07 16:35:00 (CST-6)
Location: RINGSTED
Magnitude: 52.00 EG
Property damage: 20.00K
Crop damage: 2.00K
Reported by: Newspaper

Thunderstorm Wind in BLACK HAWK, IOWA
From 16-JUL-07 19:43:00 to 16-JUL-07 19:43:00 (CST-6)
Location: LA PORTE CITY
Magnitude: 52.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:11:00 to 16-JUL-07 18:11:00 (CST-6)
Location: FARMER
Magnitude: 4.50 
Property damage: 75.00K
Crop damage: 10.00K
Reported by: Public

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:25:00 to 16-JUL-07 16:25:00 (CST-6)
Location: ESTHERVILLE ARPT
Magnitude: 53.00 MG
Property damage: 3.00K
Crop damage: 0.00K
Reported by: ASOS

Hail in BLACK HAWK, IOWA
From 16-JUL-07 18:17:00 to 16-JUL-07 18:17:00 (CST-6)
Location: CEDAR FALLS
Magnitude: 4.00 
Property damage: 300.00K
Crop damage: 5.00K
Reported by: Emergency Manager

Thunderstorm Wind in EMMET, IOWA
From 16-JUL-07 16:45:00 to 16-JUL-07 16:45:00 (CST-6)
Location: ARMSTRONG
Magnitude: 61.00 EG
Property damage: 25.00K
Crop damage: 10.00K
Reported by: Trained Spotter