The Winter Trajectory Test Program was conducted as part of the Air Weather Service Forecaster Assistance Program. The objective of this test was to determine if three-dimensional trajectories derived from the output of the Air Force Global Weather Central's six-level model are useful in the preparation of terminal forecasts. Headquarters Air Weather Service personnel evaluated forecasts prepared at detachments located in the central and eastern United States and modified some of these forecasts on the basis of trajectory information. The application of trajectory data improved the four-month verification of the terminal forecasts by 3.1%. Test procedures are discussed, and objective rules developed for the evaluation are presented.