Convective Weather Avoidance Polygon (CWAP) Algorithm Improvements and Applications

Efficiently routing air traffic around convective weather is important to safety concerns, trajectory-based operations (TBO) and maintaining cost-effectiveness for airlines. The Convective Weather Avoidance Polygon (CWAP) is an algorithm that is used to identify and forecast the boundaries of convective storms that pilots tend to avoid. Previously, the Convective Weather Avoidance Model (CWAM) produced the Weather Avoidance Field (WAF), which provided a pixel based avoidance grid where each pixel is assigned a deviation probability. CWAP improves upon this by providing storm polygons which are more accurate in portraying the boundaries that pilots tend to follow in avoiding thunderstorms.

An initial, proof-of-concept CWAP algorithm was previously developed and validated by comparing observed flight trajectories to CWAP derived from observed weather. The CWAP showed appreciable skill as a predictor of weather-avoiding trajectories in en route airspace. Many upgrades and enhancements have been made to the original algorithm to reduce its complexity and increase its flexibility without reducing its skill. Actual flight trajectory information was obtained and used in verifying the CWAP boundaries for the revised algorithm.

Techniques to improve CWAP forecasts were used and analyzed to evaluate forecast accuracy and uncertainty. Time-lagged ensembles of forecast CWAPs were created using forecast weather information from the Corridor Integrated Weather System (CIWS) and the Consolidated Storm Prediction Algorithm (CoSPA). Three to four forecast lead time ensembles were created with lead times ranging from 15 minutes to 8 hours. These ensembles as well as individual forecasts were then compared to CWAPs of coincidental observed weather to assess the accuracy of CWAP forecasts and forecast ensembles. This method generated a basis for assessing the tradeoffs of using different WAF and forecast settings for TBO applications.

CWAP improvements and enhancements as well as the ensuing validations and applications will be discussed.

This work was sponsored by the National Aeronautics and Space Administration (NASA) under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.