Automating tornado debris signature detection in the United States

The recent upgrade to the National Weather Service network of NEXRAD radars has led to a method for observing debris lofted by tornadoes. This tornado debris signature (TDS) can provide confirmation of a tornado when it is coincident with other tornadic radar signatures. This paper will present a method for automatically detecting a TDS and thus, confirming the existence of a tornado within a storm cell. The algorithm consists of detecting debris by observing low values of a smoothed dual-polarization derived correlation coefficient field. If the low values are coincident with both a reflectivity greater than 32 dBz and a tornadic vortex signature as derived from doppler velocities, then a TDS is confirmed. This algorithm is currently running in real-time using data from NEXRAD radars in the contiguous United States. The algorithm has been verified against spotter reported tornadoes during four days in the late winter and spring of 2012. During the test period, eighteen tornadoes were observed by spotters within 130 km of a NEXRAD radar site. In all 18 cases, TDS's were detected during at least part of the tornado lifespan. The tornadoes ranged in intensity from EF0 to EF4. During the test period, TDS's were detected in 47 NEXRAD volume scans, with confirmed tornadoes correlated with 45 of those TDS's. Additional statistics and case studies will be presented.