Numerical Weather Prediction and Weather Forecasting in Complex Terrain

Abstract

Numerical weather prediction (NWP) is the foundation for modern day weather forecasting. The focus of this chapter is on what NWP brings to the table when forecasting in areas of complex terrain – where it succeeds, where it fails, and how the forecaster can best use the guidance it provides. The role of the forecaster is highlighted throughout, together with reflections on alternative methods and forecasting approaches that can be used to optimize forecast quality.--> This chapter describes the advancement of numerical weather prediction (NWP) models and the role of the mountain weather forecaster in the forecast process. The chapter begins with a historical perspective of the roles NWP and the forecaster have played. This ranges from the time when models could only resolve the largest terrain features, to the present where models have shed light on processes and helped forecasters better understand features over complex terrain and improve their conceptual models. The issue of atmospheric predictability is addressed along with the inherent challenges facing the mountain weather forecaster. In some cases complex terrain actually extends predictability while for others predictability limits are relatively short and skillful forecasts are limited to hours rather than days. For each case the forecasters need to be able to recognize the salient processes and understand the differences in predictability. They must also understand the strengths and weaknesses of NWP and communicate appropriately the uncertainty of the forecast. As forecast interests expand to specific locations over a larger domain – especially in complex terrain – post processing of mesoscale NWP has become even more important. This is discussed together with a number of methodologies for downscaling NWP. Commensurate with this trend in NWP is the need for detailed observations that match current forecast resolutions. This is followed by a discussion of forecast tools and the role of the forecaster with respect to NWP. It is argued that the optimal forecast approach today is a blend of subjective techniques and statistical post-processing of NWP solutions, combined with local forecasting tools and cognitive experience. Finally, the role of the mountain weather forecaster in field programs (e.g., the Winter Olympics) gives a glimpse into the future for what may become routine. These programs shed insight into predictability limits and provide an opportunity to evaluate new observing systems, tools and approaches. The chapter ends with a vision for the future for the research and operational communities. Further exploration into mesoscale ensemble prediction and objective analysis in complex terrain, among other areas, is needed so researchers can improve mountain weather forecasting. Meanwhile, forecasters need to be open to these new advances and recognize that while their role will continue to evolve, it will also continue to be of value to society.