An incredible complex of severe thunderstorms produced widespread extreme straight-line wind damage across much of Iowa causing over $150 million in damages. $100 million of that total occurred in Polk County alone. This included the $11 million in damages initially claimed in Johnston and $726,000 in West Des Moines. Statewide, 80 homes were completely destroyed, 559 sustained severe damage, with 1416 other homes receiving moderate damage from the storm.
Areas in central Iowa particularly hit the hardest were from just northwest of Des Moines through the metro but also extended east southeast to the Mississippi River before moving on through Illinois, Indiana, and Kentucky. From the image above, this derecho lasted for several hours and brought swath of damage throughout the Midwest. In fact, this complex of storms originated in northern Nebraska during the early morning hours then moved east southeast into central Iowa where it interacted with changing atmospheric conditions and intensified further. A tornado cut an 11 mile path across Crawford County damaging dozens of residences and numerous outbuildings. Several other more brief tornado touchdowns were reported as the storms cut a path across Iowa, along with occasional large hail ranging in size up to 2.5 inches in diameter at Des Moines, but the majority of the damage was produced by very severe straight-line winds. The line of storms produced winds of 70 to 90 mph along its entire length, with embedded swaths of even stronger winds in some areas.
In the Des Moines metro area one such swath extended from around Granger through Johnston and northeastern Des Moines, with post-storm damage surveys indicating wind gusts of around 120 mph or damage to justify F2 winds. Trucks and heavy construction equipment were blown over on the interstates and hundreds of homes and other buildings were unroofed or otherwise severely damaged in the metro with countless reports of trees falling on homes. Further east the storms produced more extreme wind damage near and south of Iowa City, with an observer at Muscatine recording a wind gust of 104 mph and an unofficial instrument in Washington measuring an incredible 123 mph gust, which is the highest unofficial wind gust ever measured in Iowa. In Iowa City several cars of a freight train were blown off a railroad bridge over the Iowa River and plunged into the water below (See video below courtesy of KCRG-TV9). At the height of the storm approximately 500,000 people in Iowa were without power and in some areas electricity was not restored for nearly a week. Thousands of homes and buildings were damaged across the state and at least 125 people were injured by flying debris but fortunately there were no fatalities.
Click here for a more detailed write-up of the event in Polk County and central Iowa: http://www.weather.gov/media/dmx/SocialMedia/19980629_EventNarrative_FromStormData.pdf
Storm Prediction Center Event Summary: http://www.spc.noaa.gov/misc/AbtDerechos/casepages/jun291998page.htm
The Quad Cities NWS was also affected by the Derecho: http://www.weather.gov/dvn/ev19980629svr