Improved Forecasts of Cold Pools in Complex Terrain from WFIP2

The Second Wind Forecast Improvement Project (WFIP2) was a multiagency venture aimed at improving low-level wind forecasts in regions of complex terrain for the benefit of wind-energy applications. To achieve this objective, major modifications were developed and introduced into the Mellor–Yamada–Nakanishi–Niino (MYNN) turbulence parameterization, a component of the RAP/HRRR physics suite within the WRF–ARW modeling framework. These modifications were intended to address common RAP/HRRR forecast-error modes in the Columbia Basin and in complex terrain more generally. Among these modes, the premature erosion of surface-based cold pools was regularly observed, attended by significant forecast biases in low-level wind speeds. For wind-energy interests in the Columbia Basin, these forecast errors pose significant operational challenges.

Drawing upon high-quality measurements collected during the WFIP2 field campaign, this poster will present case studies of improved forecasts associated with cold-pool events during WFIP2. The case studies reveal that significant forecast improvements are attributable to MYNN development, but that additional improvements are achieved by other components of the WRF–ARW framework, such as refinements to horizontal diffusion. Case studies will be supplemented with results from extended retrospective tests using the RAP and HRRR models, including forecasts from a 750-m nested domain. Finally, we will reflect on the unsolved modeling challenges of WFIP2 to motivate future RAP/HRRR physics development.