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

The United States Air Force’s 45th Weather Squadron (45WS) is the organization responsible for providing weather support to Cape Canaveral Air Force Station and NASA Kennedy Space Center (CCAFS/KSC). This includes issuing warnings for hazardous weather to protect personnel, payloads, space launch vehicles, and infrastructure. One of the most impactful weather phenomena at CCAFS/KSC is convective wind events (i.e., downbursts). The 45WS issues convective wind warnings for 35 kt or greater with a desired lead time of 30 min, and for 50 kt or greater with a desired lead time of 60 min. Given that 32% of all downbursts at CCAFS/KSC produce peak winds of 35 kt or greater, the difficulty of issuing convective wind warnings and that a missed warning is much worse than a false alarm, and the very rapid development of convection in central Florida during the summer, improvements in the 45WS convective wind warnings by increasing lead time and decreasing probability of false alarm are desired.

The main goal of this study is to identify dual-polarization radar signatures that will offer increased lead times and reduce false alarms for the 45WS convective wind warnings. The 45WS uses many weather sensors, including a C-band dual-polarization radar (45WS-WSR) and the Cape Weather Information Network Display System (Cape WINDS) – a network of 29 weather instrumentation towers positioned throughout and around the CCAFS/KSC complex. In this study, the Cape WINDS was used to identify wind reports of 35 kt or greater, which were combined with radar data from the 45WS-WSR to identify storm cells responsible for these warning-level winds. Radar signatures observed within these storm cells were analyzed in an environmental context to gain an understanding of the kinematic and microphysical processes responsible for the formation of downbursts at CCAFS/KSC. Signatures observed in thunderstorms that produced downbursts with peak winds of 35 kt or greater were compared to those observed in thunderstorms that produced downbursts with peak winds less than 35 kt.

Thus far, five radar signatures have been identified to assist with differentiating between warning-level and non-warning-level downbursts at CCAFS/KSC: 1) the peak height of the 1 dB differential reflectivity (Z_dr) contour within a Z_dr column, 2) the peak height of co-located values of 30+ dBZ radar reflectivity factor (Z_h) and ~0 dB Z_dr within a storm cell, 3) the peak Z_h value in a storm cell, 4) the peak value of Z_dr within a descending reflectivity core (DRC) in a collapsing thunderstorm, and 5) the gradient of Z_dr within the DRC in a collapsing thunderstorm. These signatures were analyzed from a sample consisting of 30 warning-level downbursts (i.e., peak winds of 35 kt or greater) and 30 null downbursts (i.e., peak winds less than 35 kt). These signatures suggest the importance of melting precipitation ice in the formation of warning-level downbursts at CCAFS/KSC. The results of this analysis indicate that use of these signatures individually and/or together may offer significantly increased lead times for the 45WS convective wind warnings, especially when observed in multicellular thunderstorms. Future research will include analyzing a larger sample size, identifying other radar signatures to meet the goals of this study, and eventually integrating the results into a new multiparameter algorithm and testing that algorithm on independent convective cells.