Evaluation of WSR-88D Methods to Predict Warm Season Convective Wind Events at Cape Canaveral Air Force Station and Kennedy Space Center

Forecasting for downbursts is challenging since it is difficult to tell which convective cells will generate the downburst, when they will occur, and what the expected maximum gust will be. Nonetheless the 45th Weather Squadron (45 WS) is responsible for predicting wind gusts that exceed 35 kt, 50 kt, and 60 kt for Cape Canaveral Air Force Station (CCAFS) and Kennedy Space Center (KSC). Recently, an attempt has been made to use information from the WSR-88D's Storm Cell Identification and Tracking (SCIT) algorithm. Previous work has shown that attributes from the SCIT algorithm could be used as a precursor in nowcasting a convective wind event. Additionally, results showed an intriguing relationship between the reported wind gust and hail potential. However due to the small sample size, statistical significance was questionable and continued evaluation is needed. Also, the findings are based on the volume scan at or just before the time of the maximum reported peak wind gust. It would be more useful if this information was correlated with previous volume scans, in order to provide a longer lead-time for forecasting these events.

Using WSR-88D storm structure data of warm season convective events from 2003-2007, predicted wind gusts derived from previous methods are tested against actual peak wind gusts reported from one of the 36 weather towers located on the KSC/CCAFS complex. Scatter plots, root mean square error (RMSE), and mean absolute error (MAE) are used to evaluate the methods. In addition, new statistical techniques to predict wind gusts will be introduced in order to improve forecast skill. The performance will be verified using independent data not used to develop the technique.

Preliminary results show that the potential of previous regression-based methods does not appear to be as promising in forecasting convective wind events as originally indicated. For a much larger sample size, high RMSE and MAE values, and low correlation coefficients were measured for the time of onset, with consistent performance for earlier volume scans. However there continues to be some potential for the hail relationship. Whenever the height of the cell's maximum reflectivity is higher than the freezing level, the wind gust tends to be greater than 35 kt. These results are consistent for all volume scans. Under these circumstances, there is a high probability that hail has formed, which has been shown to be an indicator of wet microbursts. This is not surprising since large ice particles are one of the ingredients for downbursts since they provide continued cooling to sustain the downdraft over a large depth.