The Future of the HRRR: Data Assimilation Advances for Version 4

The next scheduled major update to the HRRR is scheduled for 2020, and will be the final WRF-based update. Exploratory R&D is fully underway at ESRL GSD. The data assimilation strategy will be significantly updated and improved. Current developments include implementation of either partial or continuous cycling, the use of HRRRE (i.e., storm-scale) ensemble perturbations in the hybrid 3DVar-EnKF data assimilation rather than GFS ensemble (GDAS) perturbations, fully nesting the HRRR within a RAP-like outer domain, and variations in radar reflectivity assimilation methods, including implementing an EnVar scheme for direct reflectivity assimilation, assimilation frequency, and the method of latent heating and/or hydrometeor retrieval. Initial tests suggest that partial cycling is preferred to continuous cycling, but sample size is limited, and testing is ongoing.