Improving the Maintenance of Simulated Mountain-Valley Cold Pools within Complex Terrain y Better Representation of Cloud–Radiative Interactions and Turbulent Mixing

The High-Resolution Rapid Refresh (HRRR) is a real-time operational hourly updating forecast system run at 3-km grid spacing. The HRRR uses the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) as the model component of the forecast system, but the physics suite is developed by NOAA/GSD. During the second Wind Forecast Improvement Project (WFIP2), HRRR forecasts of low-level wind in the Columbia River Basin (CRB) were compared against many deployed profiling and in-situ observational measurements. Several forecast error modes were identified, but one of the most egregious was too-shallow cold pools during the cool season, which tended to mix-out too early and result in large errors in other forecast quantities, such as turbine-height wind speed. Improvements were made within the HRRR physics suite to better represent turbulent diffusion and momentum drag. This effort alleviated this error mode, but it still remains as a forecast challenge. Subsequent (post-WFIP2) work, with a focus on improving the cloud-radiative interaction, has further reduced errors associated with the maintenance of mountain-valley cold pools.

This presentation will highlight the important HRRR model physics development and demonstrate better agreement between model simulations and observed temperature and wind profiles over the CRB. Examples of case studies and retrospective periods will be presented to illustrate the improvements at model grid spacing of 3 km and 750 m. We can also demonstrate that the improvements made in the CRB are extendable to similar phenomena in other regions, such as shallow stable layers over the Front Range of Colorado.