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A Comparison of Storm Tracking and Extrapolation Algorithms.

Abstract : The FAA requires short-term forecasts of the development and motion of high Doppler radar reflectivity regions to plan for weather avoidance in en route and terminal areas. Specific needs include choice of air routes and anticipating when to open or close approach/departure gates, descent corridors, and runways. This report compares storm-tracking algorithms for making short-term (0-30 minute) forecasts of high reflectivity areas, to serve these air traffic control control needs. Area forecasts are made by moving the key features of the current reflectivity map according to velocities derived from the storm trackers. The NEXRAD centroid, correlation, and Crane peak-cell trackers are compared against themselves, persistence, and a best-fit extrapolation, The two performance measures used are overlap of predicted versus actual areas and accuracy in flight-path choice. The second method is a new way of scoring predictor performance and is particularly suited to aviation needs. Five storms are considered, three in Massachusetts and two in Oklahoma. The correlation and peak-cell trackers generally performed well in the Massachusetts storms, close to a best correlation kit extrapolator. The centroid tracker behaves erratically, due to contour merging and splitting, but it performed well misled by storm propagation -- an effect to be expected when there is high vertical shear of the horizontal wind. It is recommended that either the correlation or centroid tracker be used, depending on the type of storm expected.