Recent and Future Advancements in Convective-Scale Storm Prediction with the High-Resolution Rapid Refresh (HRRR) Forecast System

The High-Resolution Rapid Refresh (HRRR) is a CONUS 3-km convection permitting atmospheric prediction system run hourly in real-time at the NOAA Earth System Research Laboratory. The HRRR uses a specially configured version of the Advanced Research WRF (ARW) model (including Thompson microphysics, MYJ PBL, and RUC LSM). The HRRR is run out to fifteen hours over a domain covering the entire coterminous United States using initial and boundary conditions from an hourly-cycled 13-km mesoscale model, the WRF-ARW-based Rapid Refresh (RAP). The RAP assimilates many novel and most conventional observation types including satellite observations on an hourly basis using Gridpoint Statistical Interpolation (GSI) and includes a procedure for initializing ongoing precipitation systems from observed radar reflectivity data using a digital filter, a cloud analysis system to initialize stable layer clouds, and special techniques to enhance retention of surface observation information.

Development of the 2012 RAP and HRRR forecast systems has focused on efforts to improve the depiction of the mesoscale environment through refinements to the RAP data assimilation and cloud analysis and enhancements to the model dynamics and physics. In this presentation we will (1) describe recent changes to the HRRR model configuration for 2012 to reduce a moist bias observed in 2011 RAP and HRRR forecasts including excessive soil moisture, dewpoints, precipitation and convective initiation, particularly in the first few forecast hours of each model cycle and (2) preview potential HRRR changes for 2013 with a focus on data assimilation (including radar observations) at the 3-km scale. Several approaches to the storm-scale data assimilation will be evaluated including radar-only sub-hourly cycled assimilation, 3-D-variational assimilation with partially cycled forecasts originating from the 13-km scale, and ensemble-based fully-cycled forecasts.

Select case studies including the southeastern US tornado outbreak on 27 April 2011 and the Mid-Atlantic derecho on 29-30 June 2012 will be shown to highlight both deterministic and time-lagged ensemble HRRR forecast performance.