Progress Toward Improved Solar Forecasts in Hourly Updated RAP and HRRR Forecasts

The High-Resolution Rapid Refresh (HRRR) 3km hourly updated model is now being run operationally at NOAA's National Centers for Environmental Prediction (NCEP). A focus on improved cloud/solar forecasts has been central to development of HRRRv2 and HRRRv3 experimental versions, along with the parent 13km Rapid Refresh (RAP). Experimental, advanced versions of the HRRR and RAP models are run hourly in real time at NOAA's Earth System Research Laboratory (ESRL). Since 2013, the GSD version of the model has played an important role in the Department of Energy (DOE) Solar Forecast Improvement Project (SFIP). Here, we summarize some improvements to the HRRR that have been achieved through SFIP.

Detailed solar irradiance observations from the NOAA SURFRAD network have been key to identifying issues with deficient cloudiness in the RAP and even the 3km HRRR model. Numerous changes in 2014-2015 have occurred to the physics associated with the HRRR/RAP for addressing this issue, including improved treatment of subgrid-scale cloudiness. The interaction between subgrid-scale cloud in deep and shallow convection schemes (Grell-Freitas), MYNN boundary-layer scheme, and aerosol-aware cloud microphysics will be described, with improvement demonstrated through modifications in these schemes.