Damaging Surface Wind Mechanisms within the 10 June 2003 Saint Louis Bow Echo during BAMEX

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Abstract
Detailed radar and damage survey analyses of a severe bow echo event that occurred on 10 June 2003 during the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment are presented. A bow echo formed just east of Saint Louis, Missouri, and produced a continuous straight-line wind damage swath approximately 8 km in width and 50 km in length along with five F0–F1 tornadoes. Careful superposition of the damage survey analysis and Weather Surveillance Radar-1988 Doppler (WSR-88D) data from Saint Charles, Missouri (KLSX), showed that the primary straight-line wind damage swath was not collocated with the bow echo apex as has been suggested in previous studies. Rather, the primary damage swath was found north of the bow apex, collocated with a low-level vortex that formed on the leading edge of the bow echo. Much of the primary damage swath appeared to have been created by the low-level vortex. Moreover, most of the surface straight-line wind damage was generated during the early stages of bow echo morphology prior to when the radar-detected bow echo attributes were best defined. Detailed analysis of the KLSX radar data revealed the genesis of 11 low-level meso-γ-scale vortices within the convective system. Superposition of the damage survey data showed that five of the vortices were tornadic. Careful analysis of the radar data suggests that it may be possible to distinguish between the tornadic and nontornadic vortices. Consistently, the tornadic vortices were longer-lived and stronger at low levels [0–3 km above ground level (AGL)] and rapidly deepened and intensified just prior to tornadogenesis. Similar evolution was not observed with the nontornadic vortices. All of the tornadic vortices formed coincident with or after the genesis time of the rear-inflow jet. These results suggest that the rear-inflow jet may be important for creating tornadic vortices within bow echoes. The detection and warning implications of these results are discussed.