The impact of model physics on numerical wind forecasts

Abstract

Fine scale numerical weather prediction (NWP) models are now widely applied to predict power production at wind farms. Given the fact that demand for specialized forecasts for wind farms is growing, it is important to understand the strengths and limitations of NWP models for producing wind forecasts. This paper seeks to partially fulfill this goal by exploring the sensitivity of NWP-based wind forecasts to the choice of model physics schemes. The authors used two distinct case studies to explore these sensitivities with a NWP model used in realtime wind power forecast, where the underlying meteorology in both cases had a profound impact on the wind ramp-up of a wind farm in Northern Colorado. The first case was a strong cold frontal system moving through the wind farm during winter, and the second case was for a line of strong thunderstorms passing through the wind farm during summer. The model results were compared with observed hub-height wind.In each case, sensitivity studies were conducted to explore the impact of the choice of physics schemes on the wind forecasts. For the winter case, the sensitivity to the representation of land surface and planetary boundary layer processes was quantified. For the summer case, the sensitivity to the representation of clouds and precipitation physics was explored. In the winter case, the wind forecast was less sensitive to the choice of physics schemes due to the hub-height winds being generated by strongly forced large-scale weather systems. In contrast, the wind forecast for the summer case (driven by weaker meteorological forcing) was strongly affected by the choice of cloud and precipitation physics schemes.