The complex physical processes controlling ceiling and visibility (for example, the formation, evolution and motion of low cloud, precipitation and fog) and the diverse seasonal and geographic influences that modulate these controls across the continen-tal U.S. and Alaska yield an extremely difficult analysis and forecast problem. This same phenomenology significantly impacts the safety and continuity of aviation operations, making VFR (visual flight rules) flight into impacted conditions associated with IFR (instrument flight rules) the leading cause among weather-related aviation accidents in the U.S. Recent development of an automated ceiling and visibility (C&V) forecast system for the continental U.S. has utilized expert system methodology to blend numerical and observational inputs in the synthesis of ceiling and visibility analyses and forecasts out to 10 hours. This experimental system (posted at www.rap.ucar.edu/projects/cvis) makes use of current and historical METAR data, GOES satellite observations, numerical models, MOS forecasts and observations-based ruleset forecasts. As this system matures, a similar approach will be used to provide corresponding analyses and forecasts in Alaska. This paper outlines recent progress and current functionality of the continental U.S. system. This work is carried out by the National Ceiling and Visibility (NCV) product development team under funding from the FAA’s Aviation Weather Research Program.
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