An Investigation of Downscaling Techniques to Improve Wind Analysis Background Fields in the Complex Terrain of Alaska

Southern and Southeast Alaska is characterized by tall mountains with deep narrow valleys and fjords. In some cases the mountains along the fjords rise to five or six thousand feet over very short distances. Due to the complex terrain and long distances between supply points, transportation logistics is dominated by marine and air traffic in many areas. Approximately 95% of all goods arrive to Alaska by marine transport, with air transport dominating the interior. Most of the primary ports in the state are nestled in deep complex terrain. Accurate, reliable wind forecasts in these areas are a primary concern for our Marine and Aviation Stakeholders and State and Federal partners. Because of the terrain and very active weather at times, these wind forecasts are a significant challenge to the Alaska NWS Forecast Offices. With increasing model resolution, model guidance is improving over time, though model grid spacing of well under 1 km will be required to capture most of the details. Model resolution on that order will not likely be common for a number of years, thus post-processed guidance will conitnue to be relied upon to add information. The current challenge with in developing post-processing model guidance is the lack of an adequate analysis of the wind flow on the scale required, especially given the lack of surface observations to adjust the model backgrounds used for the analysis.

Given the importance of wind forecasting in these regions, NOAAs Arctic Testbed and Proving Ground is evaluating different methods to downscale winds to provide an improved analysis and forecast information to our forecasters. A few the ideas we are currently evaluating are various divergence minimization techniques, Multiple Discriminate Analysis, and pressure gradient guidance based decision tools. Current results from our evaluations will be presented. We hope to foster discussion to learn of new potential ideas for future discussion.