Ceiling and visibility (C&V) conditions near the earth’s surface are controlled through a complex balance of meteorological phenomena. Key among these are (i) the formation and evolution of fog, low cloud, and precipitation, and (ii) humidity, haze and aerosol effects. Diverse seasonal and geographic influences further modulate these controls, making C&V phenomena an extremely challenging analysis and forecast problem. The operational importance of that problem, however, is underscored by the serious negative impacts that adverse C&V conditions bring to the safety and efficiency of aviation operations and surface transportation.

Recent development of an exploratory C&V forecast system for aviation use in the continental U.S. has utilized expert system methodology to merge numerical and observational inputs in the synthesis of forecasts out to six hours. Its products (posted at www.rap.ucar.edu/projects/cvis/index.html) have yielded encouraging early results and useful insight into needs for future development. This paper describes current and emerging work associated with data access, hybrid application of numerical and statistical modeling, expert system processing, statistical verification, and interactive display techniques used in development of the system.

The current system is built around an expert system framework that manages the dynamically weighted integration of a growing number of analysis, forecast and verification components, as outlined below:

(i) ASOS reports and GOES imagery are used to produce a U.S. national analysis of current ceiling, visibility and flight category conditions updated four times per hour on a 20 km grid. Broader use of GOES products, NRL cloud classification routines, and NEXRAD data are in development for use in gap-filling, as guidance for ‘smart’ interpolation, and incorporation in other analysis processes.

(ii) The forecast function is currently built around a dynamically weighted combination of hourly forecast fields from the RUC model and persistence forecasts. Incorporation of Eta model forecasts, statistical forecasts (utilizing climatology, current observations and NWP model results), and use of the high-resolution COBEL boundary layer column model at selected sites are in development.

(iii) Verification and evaluation of forecast results are logged and available on an ongoing basis through the NOAA/FSL Real-Time Verification System (RTVS) posted at www-ad.fsl.noaa.gov/fvb/rtvs/index.html. Expansion of RTVS processing and display capabilities, improvement in the expert system performance feedback loop that helps guide component weighting, and focused diagnostic case studies of critical C&V events will improve fundamental system performance as well as capability to examine and track that performance.

The paper will highlight technique development concepts and their application to the C&V forecast system.