May 21 - July 30
Determining the Likelihood of Observing the Tornado Article Debris Signature at Different Geographic Locations throughout the United States
Shawn Handler, Valliappa Lakshmanan, Terry Schuur, and Matthew Van Den Broeke
What is already known:
- With the upgrade to dual-polarization radar, it has become possible to use new radar moments to detect tornado debris, specifically with the use of the tornado debris signature (TDS).
- Criteria used for detecting the tornado debris signature on radar have been researched extensively.
- Little research has looked into observing the tornado debris signature at different geographic locations throughout the United States based on different radar, environmental, and societal variables.
What this study adds:
- Given that there is an ongoing tornado, overall likelihood maps were created for three seasons to best represent the likeliness of observing a TDS.
- Results have shown that it would be most likely to observe a TDS for tornadoes of EF2 or greater intensity. However, the lowest unblocked height of a radar beam dictates if the TDS will be seen.
- Forecasters could apply these maps to determine whether a TDS depicted on radar is in a likely or unlikely area for detection which would be helpful for verifying tornado warnings.
Abstract:
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.