Using C-Band Dual-Polarization Radar Signatures to Improve Convective Wind Forecasting at Cape Canaveral Air Force Station and NASA Kennedy Space Center

Convective wind events have a major impact on operations at Cape Canaveral Air Force Station and NASA Kennedy Space Center (CCAFS/KSC). These wind events pose considerable risks to the range safety of personnel and the protection of costly equipment and space mission payloads at CCAFS/KSC. The United States Air Force’s 45^th Weather Squadron (45WS) is the organization responsible for monitoring weather conditions and issuing warnings for hazardous weather events (including convective wind events) at CCAFS/KSC. Over the past several years, various improvements in radar technology have been implemented at CCAFS/KSC, including the addition of a C-band radar that offers dual-polarization capabilities. Dual-polarization radar products can be useful when identifying features within thunderstorms that are conducive to the formation of damaging convective wind events (e.g., microbursts). This study is one of the first to examine dual-polarization radar signatures within microburst-producing thunderstorms at CCAFS/KSC using the C-band radar that is primarily used by the 45WS during their operations. Although past studies have focused on operational WSR-88D (S-band) data from Melbourne, FL, the strategically-placed location of the radar relative to the CCAFS/KSC complex, the frequent use of the radar by the 45WS, and the finer radar data resolution are some benefits of performing this study using the 45WS’s C-band weather surveillance radar (WSR).

The goals of this research project are twofold. The first goal is to increase lead times and decrease false alarm rates for convective wind warnings issued by the 45WS by identifying dual-polarization radar signatures that are common amongst microburst-producing storms at CCAFS/KSC. The second goal is to identify dual-polarization radar signatures that can be used to differentiate between storms that will produce peak wind gusts between 35 and 49 knots (the first warning threshold used by the 45WS) and those that will produce peak winds of 50 knots or greater (the second warning threshold used by the 45WS). In addition to the WSR C-band data, environmental conditions were analyzed using sounding data from the KSC Skid Strip (KXMR). Convective wind gusts were examined using the Cape Weather Information Network Display System (WINDS) tower network at CCAFS/KSC. All data were provided by the 45WS and the Air Force’s 14^th Weather Squadron. A total of 91 convective wind events have been identified, all of which occurred during May – September 2015 and six of which have been analyzed so far. Analysis of radar vertical cross sections was performed at various times throughout the lifecycle of each microburst-producing storm cell to identify common dual-polarization signatures. When placed in an environmental context, the dual-polarization radar signatures can be used to infer kinematic and microphysical processes associated with microbursts, which can then lead to radar algorithms that address the two main goals of this study.

Preliminary results indicate that examining values of differential reflectivity (Z_dr) within a “Z_dr column” above the environmental 0 °C level may offer increased lead times for microburst events. A Z_dr column value of 1 dB extended above the environmental 0 °C level 6.5 – 28.5 minutes before the time of the microburst in all cases analyzed so far and offered at least 20.5 minutes of lead time in four of the six cases analyzed. Additionally, the peak value of Z_dr within a Z_dr column at or above the level of minimum environmental equivalent potential temperature (θ_e) may offer increased lead times for microburst events. In all cases analyzed so far, a Z_dr column value of 2 dB or greater was present at or above the level of minimum θ_e 6.5 – 25.5 minutes before the time of the microburst, with this signature offering at least 17.5 minutes of lead time in four of the six cases analyzed.

Future work will include further examination of Z_dr columns using the remainder of the 91 microburst events identified from 2015. Other dual-polarization, single-polarization, and Doppler features will also be identified to meet the two main goals of this study. All of these signatures will be compared to null events (i.e., convective wind events with a peak wind gust less than 35 knots) to examine differences between storms that produce microbursts that meet the 45WS convective wind warning thresholds and those that do not. The results of this study will eventually be included in a new algorithm that will be supplied to the 45WS to assist with their forecasting of convective wind events.