An Operational Three-Dimensional Trajectory Model

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Abstract
A numerical model is developed to compute three-dimensional trajectories from operational wind forecasts generated by the six-layer primitive equation model of the National Meteorological Center. Detailed 24-hr forecasts of temperature and dew point, designed for application to severe storm prediction, are derived by computing the 6-hr variations of potential temperature and mixing ratio for air parcels assumed to follow paths defined by the trajectories. Initial values at the trajectory origin points are provided by an objective analysis technique which reproduces detailed patterns and gradients with only light smoothing of the observations. The influence of a relatively detailed terrain is also included in the program. Verification statistics indicate a significant improvement over the primitive equation model forecasts in the lowest 150 mb, where temperature and moisture distributions are crucial to severe storm development. Output from the model for the surface, 850 and 700 mb is currently transmitted via National Weather Service facsimile and teletype circuits for use as guidance in severe storm forecasting.

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