Identifying Downburst Precursor Signatures in KDP

Downburst-producing storms that develop in low-shear environments pose a significant forecast challenge to National Weather Service (NWS) forecasters especially across the southeast United States where these events are common during the summer months. The dual-polarization upgrade to the national WSR-88D network provides forecasters with an opportunity to examine signatures that were previously unavailable to them. One such signature that may be useful in short-term forecasting of downbursts is an enhancement of K_DP near and below the environmental melting layer known as a K_DP core. Characteristics of this signature can alert forecasters to processes such as melting and evaporation which enhance negative buoyancy within a downdraft thereby increasing the risk for damaging downbursts at the surface.

The purpose of this study is to examine K_DP core characteristics (e.g., magnitude; size; depth) and near-storm environments to provide forecasters with information that could help them anticipate these potentially damaging events and therefore increase warning confidence and lead time. Multiple cases from various geographic locations were analyzed and time series plots were created of K_DP core and reflectivity core evolution prior to downburst development and maximum intensity. The documentation of microphysical fingerprints also provided information about processes such as melting and evaporation. Rapid-scan (volume update times of less than 2 min) dual-polarization data collected by a research WSR-88D located in Norman, Oklahoma were also analyzed to see what impact volumetric update time has on effective sampling of K_DP cores. The lead author will discuss key findings of this ongoing study.