Damage Assessment and Radar Analysis of the 10-11 July 2011 Derecho in Iowa

A cluster of thunderstorms initiated in southwest Nebraska during the early evening hours of 10 July 2011, moved eastward and evolved into a bow echo complex in western Iowa after midnight, then continued east producing a three-county-long swath of extreme winds in excess of 45 ms-1 (100 mph) in east-central Iowa toward sunrise. The storm complex persisted through the daylight hours, eventually reaching the Mid-Atlantic states.

The damage path was extensive, stretching from the central Plains to the East Coast. Numerous reports of high winds or damage were received suggesting wind speeds of 32 ms-1 (70 mph) or higher, but no tornadoes were observed. However, it was while the storm traversed east central Iowa that, by far, the most significant damage, equivalent to a high-end EF2 tornado, occurred.

This study will describe the nature of the most extreme damage produced by the bow echo in east-central Iowa, and the environment in which the event occurred with particular emphasis on factors that may have been unique to the area where the most extreme winds occurred. In addition, a detailed analysis of the evolution of the bow echo's cyclonic circulation and a comparison to damage reports will be presented.