The Relationship Between Tornadic Debris Signature Height and Tornado Intensity
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Monday, 5 January 2015
The National Weather Service (NWS) recently completed the process of upgrading the WSR-88D radar network with dual-polarization (dual pol) technology. During this short period of dual pol operations, benefits of this technology have already been observed from the proper use of specific products. While the radar upgrade offers a number of improvements and new products, of particular interest is the detection of tornado debris. The tornadic debris signature (TDS) can be observed when there is a lowering of the correlation coefficient (CC) and lowering of differential reflectivity (ZDR) to near zero, both collocated with higher reflectivity (Z) >30-35 dBZ and a valid circulation in the velocity data. This signature has been documented many times over the past two severe weather seasons. It has been extremely helpful during recent impactful tornado events, especially the April 28, 2014 event, where testing of the Impact Based Warnings was underway at NWS Jackson, MS. Additionally, this signature has helped the NWS find weaker tornadoes that may have otherwise gone un-surveyed.
This study builds on a previous one that determined there is a relationship between maximum TDS height and tornado intensity. The dataset now exceeds 180 cases. These added data make the correlation more robust and strengthens the relationship between TDS height and tornado intensity, especially when the data are stratified by storm mode. The latest research continues to indicate when debris is lofted to 10 kft or greater, the potential for a strong/significant tornado becomes increasingly likely. The end goal of this research is to increase the confidence of the warning forecaster in the likelihood of a damaging/significant tornado occurring based on the dual pol data. Such increased confidence can allow the forecaster to enhance wording in tornado warnings and issue potential tornado emergencies, especially as the NWS moves into the Impact Based Warning era.