E-Journal of Severe Storms Meteorology

E-Journal of Severe Storms Meteorology, Vol 2, No 3 (2007)

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Preliminary Observations of Weak Three-Body Scatter Spikes Associated With Low-End Severe Hail

T. Todd Lindley, Leslie R. Lemon


The three-body scatter spike (TBSS), an artifact caused by radar microwave scattering associated with large hydrometeors, traditionally has been utilized in the National Weather Service as an operational indicator of destructive hail. Severe weather warning strategies based on the TBSS were derived using a lower-bound reflectivity threshold of 5 dBZ. With recent WSR-88D workstation software and product upgrades, the operational display of very low value reflectivity data to -30 dBZ has allowed meteorologists to observe more subtle, but meaningful, atmospheric targets and artifacts. Since these upgrades, radar-based interrogations of thunderstorms over west Texas and South Dakota (among other places) have revealed weak TBSS signatures characterized by faint radar returns as low as -14 dBZ. A sufficient dataset of weak TBSS cases does not exist currently to support a robust statistical analysis. Preliminary observations, however, indicate that the artifact may occur prior to and during low-end severe hail measuring between 1.9 cm and 2.5 cm in diameter, especially when recognized to emanate from pulse-type convective storms sampled at close range over the Great Plains. These observations suggest that an extension to the current conceptual use of the conventional TBSS model, which associates the traditional signature to a likelihood of "very large hail," should be investigated.

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