A Comparative Analysis of Tornadic Debris and Debris Fallout Signatures from the 10 – 11 December 2021 and 28 – 29 May 2019 Tornadoes

It is commonly known that the leading cause of structural damage and personal injury during a tornado is the lofting and ejection of debris. The radar signature associated with the lofted debris is called the tornadic debris signature (TDS) and is used to estimate tornadic strength. A less commonly seen signature is the debris fallout signature (DFS) – a signature that is present when a large amount debris is advected away from the tornado. The DFS causes additional impacts, as the debris fallout can occur in clear air. The Linwood, Kansas EF4 on 28 – 29 May 2019 and the Mayfield, Kentucky EF4 in 10 – 11 December 2021 each produced a prominent TDS and DFS, both of which are examined using the Weather Surveillance Radar-1988 Doppler (WSR-88D) network. The goal of this study is to assess the evolution and impacts of the TDS and DFS during these two outbreaks. The radar data was gridded onto a 1 km x 1 km x 0.5 km grid using Barnes interpolation in PyArt. Both the TDS and DFS were manually detected at each height and time step, where ρ_HV < 0.9 and Z_H > 10 dBZ. Additionally, debris reports were collected by the NWS for the Linwood, Kansas tornado. In both cases, results show that the evolution of the DFS is not a continuous process, but rather evolves in bursts. In the Linwood, Kansas case, the areal extent of the DFS reaches a maximum shortly after the TDS height reaches a momentary peak. The same evolution is not seen in the Mayfield, Kentucky case, as the DFS evolution stems from two sources – debris being lofted from the top of the TDS and the tornado ejecting debris to the northwest at low-levels. The temporal evolution of the minimum value of ρ_HV within the TDS and DFS will also be examined, in addition to a comparison of the DFS orientation to the environmental winds.

The DFS in the Linwood, Kansas case impacted operations at the Kansas City International Airport, as debris fell onto the runway. The falling debris was up to 50 miles away from the Linwood, Kansas tornado, showcasing that the impacts of debris can extend well beyond the tornado. Furthermore, the DFS can persist well after the tornado has dissipated. The results from this study are useful for operations as the evolution of the DFS is largely unknown and can have important societal impacts.