Improvements to HRRR Wind Forecasts from WFIP2

The Wind Forecast Improvement Project II (WFIP2) is a multiagency venture aimed at improving low-level wind forecasts in regions of complex terrain for the benefit of wind-energy applications.  To support this objective, experimental modifications to the  Mellor–Yamada–Nakanishi–Niino (MYNN) turbulence parameterization are being tested within the WRF–ARW modeling framework.  A provisional version of NOAA's 3-km High-Resolution Rapid Refresh (HRRR) model, the HRRR–WFIP2—which includes a 750-m nest—provides a platform for real-time and retrospective forecasting using experimental MYNN scheme modifications, and serves as a pathway for eventual operational implementation of improved model parameterizations developed during WFIP2.

Drawing upon in-situ measurements collected during the WFIP2 field campaign, this presentation documents improved HRRR low-level wind forecasts in the WFIP2 study region and throughout the continental U.S.  Forecast improvements are largely attributed to MYNN modifications, most notably (1) a significant revision to the MYNN length-scale formulation, and (2) the addition of a mass-flux parameterization for both dry and cloudy convective plumes.  However, the impact of modified WRF–ARW numerics, including the hybrid vertical coordinate and horizontal diffusion capabilities, will also be discussed.  Forecast improvements from single-run case studies and retrospective test periods, using the 3-km HRRR and a 750-m nest, will be presented, providing evidence that the experimental MYNN modifications are suited for general forecast application across a range of model horizontal grid spacing.