The impact of an enhanced damage analysis on determining the damaging wind mechanism within the 20 August 2007 bow echo across eastern Nebraska and southwestern Iowa

At approximately 1900 UTC on 20 August 2007, storms developed along the central KS/NE border associated with modest boundary layer convergence along a surface trough and axis of strong surface heating. Effective bulk shear on the order of 30-35 kt supported organized multicells and some supercell structures within this very moist/unstable air mass. In addition, the deeply mixed environment was also conducive for strong downdrafts. By 0000 UTC, the system had grown upscale into a QLCS. Over the next two hours, a portion of the system bowed outward as it swept through the Omaha metropolitan area.

Over the course of the week following the event, several undergraduate students and a faculty member from the Department of Atmospheric Sciences conducted some simple damage analysis. Armed with a GPS-enabled digital camera (Ricoh 500SE) and a hand-held Garmin GPS unit, we attempted to document the fairly extensive damage that occurred in and around the Omaha area. The damage data were then related to the Level II radar data from the WSR-88D at OAX in an attempt to understand what portions of the convective system produced the damage observed at the surface. The results showed that the most significant surface damage occurred on the southern periphery of an intense low-level circulation that developed along the leading edge north of the apex of the bow. Additionally, the results highlighted the inadequacy of the standard reporting system when used to examine marginal and/or non-tornadic events for which the NWS does not conduct an analysis.