Bow echoes during BAMEX: assessing transitions in surface wind damage using WSR-88D data

Data obtained from ten intensive operation periods (IOPs) that focused on the evolution and life cycle of mesoscale convective systems (MCSs) and associated bow echoes during the Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX) are used to investigate the temporal evolution of damage in MCSs that develop from individual cells and exhibit well-developed trailing stratiform precipitation.

For the ten IOPs, one of five possible radar signatures was assigned at the locations of damage reports routinely archived by the National Weather Service and those specifically collected during BAMEX. These were as follows: rotational couplets, macroburst/microburst couplets, rear-inflow, peripheral gust fronts, and indeterminable. At each damage location, quantities from the WSR-88D level II and level III radar data such as beam height, orientation angle of the radar beam to the convective line and maximum radial velocity were also determined. When a rotational or downburst couplet was present, the total shear across the couplet and its diameter were determined. When a descending rear-inflow jet was present, its maximum radial velocity was measured. These data were used to quantify the relationship between the reported and surveyed damage and the radar velocity signature at the location of each damage report and/or survey.

The damage associated with the descent of the rear-inflow jet peaked between one and three hours after its establishment and the number of rotational and macroburst couplets peaked about one hour prior to the development of the rear-inflow jet, illustrating a transition in the mode of the winds producing the damage for all these IOPs. The presentation will detail examples of the radar signatures and the difficulties encountered when assessing damage causes using single-Doppler radar analysis. The results and implications of the damage transition will be discussed.