Severe Storm Detection Algorithms for the S2000 Project

Several detection systems were involved in providing diagnoses and nowcasts of severe weather, both from Doppler and polarization radar data. They included the NSSL Warning Decision Support System (WDSS), the Canadian Radar Decision Support (CARDS) system, two versions of TITAN, and a precipitation-typing algorithm, detecting hail from the polarized CPOL radar. Radar software algorithms attempted to detect the presence of cells, mesocyclone circulations, bounded weak echo regions, tornadic vortex signatures, downbursts/microbursts, hail, and lightning. Cell tracking provided extrapolation nowcasts. The detection outputs from the various systems were integrated via the Thunderbox system.

Radar data were collected in a dual-PRF mode which introduced dealiasing artifacts into the data. A median filter was applied to the data to remove these errors. In a broad sense, WDSS and CARDS ran similar detection algorithms though they varied in their degrees of sophistication. WDSS provided cell or storm classifications based on inputs from all the algorithms, whereas CARDS provided classifications on an individual algorithm basis. TITAN and WDSS both provided cell detections and cell tracking. TITAN cell detections were set up with different thresholds (35 and 45 dBZ) to attempt to detect and track weaker cells. WDSS and CARDS Circulation algorithms were adapted to the southern hemisphere. Radial-velocity-based and reflectivity-based downburst algorithms were available from WDSS and CARDS. Three different hail algorithms from WDSS, CARDS, and CPOL provided output on presence, probability, and size of hail. Display of all the hazard outputs were available on each of the individual systems, but storm properties and algorithm detections were also used as input to the Thunderbox system to produce human-editable graphical depictions. Comparisons of and experiences with the various systems during S2K will be described.