A study of mountain-forced wind, wind-shear and turbulence was conducted in order to reveal general characteristics of terrain-induced turbulence nearby airports in mountainous areas. Special studies of the topography close to a number of Norwegian airports that currently receive hourly forecasts of terrain-induced turbulence were also performed. It was found that there is a potential for improving efficiency and robustness as well as accuracy of the micro-scale code at the end of the nested set of numerical weather prediction codes that each resolves different scales and which is used in the forecasting mentioned. The optimizing was done by tuning the shape, size and orientation of the local regions as well as the quality of the spatial grid within the regions. The continuous increase of computational power opens for utilizing finer and larger forecast grids for airport regions with topography that are not resolved with the present grids. This gives promise to using these finer micro-scale grids in operational forecasting in near future. A rough estimate of the present realistic and operational grids is a doubling of grid density horizontally as well as increasing grid density vertically by a factor 1.5 as compared with existing numbers. The selected airports were investigated in order to deduce general as well as specific guidelines regarding optimum size, shape and orientation of the micro-scale forecast region relative to the local topography nearby the airports. Details for the selected airports are found in the conclusion section of the report. Oppdragsgiver: Avinor AS

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