Evolution of the hook echo and low-level rotation in the 17 May 2000 Brady, NE supercell

The Doppler on Wheels collected a unique close-range radar dataset of a rapidly intensifying tornadic supercell near Brady, NE on May 17, 2000. The radar volume scan strategy featured frequent 1 minute volume scans extending from low altitudes (~200m) to middle and upper altitudes (5-7km) of the storm, allowing the study of the small-scale detail near the ground and the larger-scale storm structure and evolution. The data depicts the evolution of the hook echo and low-level rotation in high temporal and spatial detail, as well as other important related features including: cell mergers, storm-boundary interactions, enhanced low-level horizontal vorticity on a storm-scale boundary, reflectivity “blobs” on the rear flank, a large updraft pulse visible on the rear-flank, and a rear-flank downdraft surge. This study illustrates how the significant changes in hook echo structure are related to: horizontal advection in rotation aloft, hydrometeors ingested in low-levels by a weak merging cell, a very large updraft pulse on the right-rear of the storm, and a mix of precipitation cascade and horizontal advection nearer to the ground. The study also discusses the development of the rear-flank downdraft surge and its relationship to the hook echo and the development of low-level rotation.