Event Summary:A squall line developed north of a stationary front across Southern Iowa into Northern Illinois in a near tropical atmosphere.  The squall line moved east and bowed out as it moved through Benton, Linn, and Jones Counties in Iowa.  Spotty severe wind was reported in the northern parts of Iowa and Johnson counties.  A bookend vorticy developed on the squall line in Jones county and moved through Jackson County Iowa and into northwest Carroll County Illinois.  Another small bowing of the squall line occurred across Whiteside County Illinois. The storms in the squall line were prolific lightning producers which caused severe damage to a house in Farmington, Iowa.

Thunderstorm Wind in CARROLL, ILLINOIS
From 03-AUG-04 19:00:00 to 03-AUG-04 19:10:00 (CST)
Location: MARCUS
Magnitude: 57 EG
Property damage: 5K
Crop damage: 2K
Reported by: TRAINED SPOTTER

Bookend vorticy of squall line left Jackson County Iowa and entered Carroll County Illinois around 1900 CST (0100 UTC) near Marcus.  Only damage reports received were that of large limbs down that took two people to move on Illinois 84 during 1902-1907 CST.  The location is between 0.2 miles north northeast of Marcus near the golf course to 0.4 miles east northeast of Marcus near the northwest edge of Mississippi Pallisades State Park.  The sheriff department indicated additional trees down on Senic Ridge Road during 1904-1909 CST.  The location is likely between the Jo Daviess/Carroll county line and the northeast edge of Pallisades State Park.  Although no additional reports of severe winds were received, KDVN 88D data suggests the potential for additional wind damage across the rest of Washington township, and across Woodland into Freedom townships to a development around Lake Carroll.

Thunderstorm Wind in WHITESIDE, ILLINOIS
From 03-AUG-04 19:05:00 to 03-AUG-04 19:55:00 (CST)
Location: COUNTYWIDE
Magnitude: 57 EG
Property damage: 10K
Crop damage: 5K
Reported by: TRAINED SPOTTER

Squall line left Clinton County Iowa and entered Whiteside County Illinois around 1900 CST (0100 UTC).  Sporatic damage consisting of mainly trees and power lines down occurred across the northern part of the county from near Garden Plain, to Morrison, to north of Sterling.  Trees were reported down on Elston Road during 1902-1907 CST.  The exact location is not known but the likely area is between Fulton and Garden Plain with the immediate Garden Plain area being most probable.  The KCWI AWOS reported 44 knots ( 51 mph) during 1845-1855 CST in Clinton County Iowa.  Considerable damage occurred during 1915-1920 CST along Norrish Road, Hazel Road, and the intersection of Bishop and Holly Roads immediately to the north and east of Morrison.  A large number of trees were downed along with power lines.  The KDVN 88D showing a considerable increase in wind speed in this area to at least 60 knots aloft.  Additional tree and power line damage occurred at the intersection of Holly and Habben Roads during 1923-1928 CST and the intersection of Flufs and Hoover Roads during 1944-1949 CST.  The second location is located several miles north of Sterling.  The KSQI AWOS south of Sterling reported 41 knots (47 mph) during 1945-1955 CST.  Another area of damage occurred in the Coleta area during 1935-1942 CST with reports of trees and power lines down.