Determining the Likelihood of Observing the Tornado Debris Signature at Different Geographic Locations throughout the United States

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Sunday, 4 January 2015
Shawn Handler, CAPS/Univ. of Oklahoma, Auburn, ME; and V. Lakshmanan, T. J. Schuur, and M. S. Van Den Broeke

With the upgrade of the National Weather Service network of weather radars to dual-polarization, it has become possible to use the new radar moments to detect tornado debris. This study investigates the likelihood of observing the tornado debris signature (TDS) at different geographic locations throughout the United States given that an ongoing tornado is present. The likelihood of observing a TDS varies according to radar geometry and the presence of materials that can be lofted by a tornado. To estimate the likelihood of observing a TDS at different geographic locations, we employed datasets of range from the nearest radar, lowest unblocked height of the radar beam, population density, and a normalized differenced vegetation index (NDVI). We also modeled the relationship of tornado intensity and the vertical extent of the debris signature. Maps for three distinct seasons in 2012 (spring, summer, fall) were generated identifying areas where TDS detection would or would not be likely for tornadoes of EF0-EF2 and EF3+ intensities. The study indicates that a tornado is likely to be depicted by a TDS on radar if it occurs in regions of close proximity to the radar site, high population density or rich vegetation, and if the tornado itself is strong. The signature is less likely to be seen for weak tornadoes, rural areas that have little vegetation, and regions that experience beam blockage. Tornadoes of EF0 or EF1 intensities are unlikely to exhibit a TDS, and in some areas, like the Gulf Coast, the TDS may only be observed for tornadoes of EF3+ intensity. The range of TDS detection was also found to be limited in areas susceptible to tornadoes which included portions of the Central Plains, Midwest, and Mississippi Valley.