Toward Generating a New Gridded Ceiling and Visibility Product for Alaska

Ceiling and visibility (C&V) hazards are of vital concern to general aviation interests in Alaska where controlled flight into obstructed terrain is one of the top causes for aircraft incidents. The limited number of surface stations, infrequent overpasses by polar orbiting satellites, steep viewing angles of geostationary satellites and unknown performance of NWP models across Alaska make the development of a gridded C&V product for Alaska a difficult proposition. In addition, much of Alaska is influenced by complex terrain and/or coastline which limits the representativeness of the surface observations that do exist. In order to fill gaps between observing stations, the FAA Weather Camera Program has installed two or more horizontally-looking cameras at over 200 sites across Alaska to fill in gaps between METAR sites especially in areas of complex terrain.  The FAA Aviation Weather Research Program (AWRP) is funding a collaborative effort to develop a gridded C&V product using a combination of available observations (including estimates of visibility derived from camera imagery) and model analysis data. The goal of this project is to develop data fusion techniques that can combine a suite of observations into a single rapidly-updating gridded C&V analysis product that will aid Alaskan Aviation Weather Unit forecasters in preparing TAFs and gridded C&V analysis and forecast products. A baseline C&V product that combines METAR data with analyses from the Rapid Refresh (RAP) model running at NCEP using a heuristic tiling approach is discussed. Because the model serves as the base layer of the gridded C&V analysis product, knowledge of model performance is critical for interpretation of the product. It is found that the model has systematic biases in its representation of both ceiling and visibility hazards. Seasonal and regional variations in these biases and methods that could be implemented for bias correction are discussed. Finally, the value added by using satellite data to produce the C&V product is assessed.

This research is in response to requirements and funding by the Federal Aviation Administration (FAA).  The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.