The High-Resolution Rapid Refresh (HRRR): An Hourly Updating Convection-Allowing Forecast Model. Part I: Motivation and System Description

Abstract The High-Resolution Rapid Refresh (HRRR) is a convection-allowing implementation of the Advanced Research version Weather and Forecasting (WRF-ARW) Model with hourly data assimilation that covers conterminous United States Alaska runs in real time at NOAA/National Centers for Environmental Prediction (NCEP). Implemented operationally NOAA/NCEP 2014, HRRR features 3-km horizontal grid spacing frequent forecasts (hourly CONUS 3-hourly Alaska). initialization designed optimal short-range forecast skill particular focus on evolution precipitating systems. Key components are radar-reflectivity assimilation, hybrid ensemble-variational conventional weather observations, cloud analysis to initialize stratiform layers. From this initial state, produced out 18 h every hour, 48 6 h, boundary conditions provided by system. Between 2014 2020, development was focused reducing model bias errors improving realism accuracy. Improved representation planetary layer, subgrid-scale clouds, land surface contributed extensively overall improvements. final (HRRRv4), implemented late also using flow-dependent covariances from 3-km, 36-member ensemble (“HRRRDAS”) explicit convective storms. HRRRv4 includes prediction wildfire smoke plumes. provides baseline capability evaluating NOAA’s next-generation Forecast System, now under development. Significance Statement operational updating, model, (HRRR), key tool forecasting situational awareness. Improvements as well physics parameterizations, have led improvements simulated radar reflectivity quantitative precipitation since September 2014. Other targeted has improved diurnal cycle resulting near-surface temperature humidity forecasts. Additional changes treatment erosion low-level including clouds. storm-scale