Today's trend in probabilistic weather forecasting is toward utilizing ensemble prediction systems. In the Next Generation Air Transportation System (NextGen), ensemble-based weather forecasting will be a common practice. Therefore, this paper explores a novel approach of using highresolution, ensemble-based numerical weather prediction model data for weather-related, probabilistic aviation impact forecasting. The concept represents a paradigm shift from "creating ensembles of weather information" (e.g., maps of predicted weather hazard intensity) to "developing ensembles of aviation-relevant information" (maps of potential throughput as measured by the available flow capacity ratio), which entails a translation of weather forecasts into predictions of reduced airspace capacity. The proof-of-concept is exemplified by focusing on convective storms; however, in principal, the approach may be applicable to other aviation hazards, like turbulence, icing, or ceiling and visibility. The concept is most pertinent to strategic en route traffic flow management, but it also applies to terminal area applications. A probabilistic approach is appropriate for strategic planning horizons, for which deterministic weather forecasts are significantly less accurate and an ensemble of forecasts may provide guidance about the weather (and impact) uncertainty.

Low cloud ceilings and poor visibility claim the lives of more general aviation (GA) pilots and passengers than any other cause of weather-related GA accidents. Experience shows that instrument-rated pilots as well as those rated only for visual flight are vulnerable to low ceiling and visibility (C&V), making total avoidance the most powerful strategy available to a GA pilot dealing with these hazards. The weather awareness needed for avoidance begins with the recognition of current conditions. This article outlines how fusion of surface, satellite, and terrain data yields a graphical analysis product that enables GA pilots, dispatchers, and weather briefers to better visualize the areal distribution of recent and current C&V conditions across the contiguous U.S. The product is available at www.aviationweather.gov/adds/cv and indicates ceilings less than 1,000 ft above ground level, visibilities less than 3 statute miles, and regions where terrain obscuration is possible. The product is also viewable in the context of interactive geographic information system data via the experimental Helicopter Emergency Medical Services Tool available at http://weather.aero/tools/desktopapps/hemstool. The authors summarize verification results and outline work toward a next-generation product that incorporates the use of model forecast data and weather camera imagery to improve information in data-sparse regions. This next-generation product is in development for initial use in Alaska.