A Characterization of NWP Ceiling and Visibility Forecasts for the Terminal Airspace

Capacity changes associated with ceiling and visibility restrictions can have a significant impact on terminal ATC operations. The FAA's Aviation Weather Research Program (AWRP) sponsors the Terminal Ceiling & Visibility Product Development Team (PDT) to develop tools to mitigate the impact these adverse conditions on efficient and safe use of available capacity. In particular, the PDT is currently investigating product development for C&V conditions associated with large, transient weather systems that impact the Northeast United States during the winter months. The project goal is to provide automated C&V guidance to the air traffic managers for both the tactical (0-2 hour) and strategic (3-12 hour) decision-making time horizons. To meet these requirements, particularly in the strategic time frame, a comprehensive C&V system will need to incorporate guidance from an explicit numerical weather prediction (NWP) model.

This study provides a brief comparative statistical forecast accuracy assessment of the NWS Terminal Aerodrome Forecast (TAF), NWP, and persistence forecasts tailored to address specific terminal C&V operational decision points. Ceiling and visibility forecast output from three NWP forecast models, the Rapid Update Cycle (RUC), National Center for Environmental Prediction (NCEP) ETA model, and the fifth generation Pennsylvania State University (PSU)/ National Center for Atmospheric Research mesoscale model (MM5) were evaluated. In addition to assessments of mean and standard deviations of the categorical forecast accuracy this analysis also examined non-standard forecast accuracy associated with trends and spatial variability in the high-resolution simulations. This study concludes with recommendations for where to proceed with further accuracy assessments and suggestions for near term implementations of the NWP C&V forecasts into the automated terminal ceiling and visibility decision support tool.