Here, we describe the HRRR initialized from the 13km RUC/RR radar reflectivity assimilation method. The HRRR represents a first for hourly updated, storm-scale model forecasts including hourly radar reflectivity assimilation and has considerable promise for short-range thunderstorm prediction. Hourly output grids from the HRRR are an integral part of the CoSPA merged convective guidance demonstration product. The HRRR has shown particular skill at accurately depicting storm mode, which is especially important for providing en-route aviation guidance. Also, the hourly output and hourly update frequency of the HRRR provide a large number predictors for the possible creation of a HRRR-based convective probability guidance product.
The HRRR is currently nested over the northeastern US inside the 13km backup RUC run at NOAA/ESRL/GSD, run on a 1h cycle, and uses a version of the WRF model but does not include convective parameterization. It relies on the RUC13 data assimilation, which includes radar reflectivity assimilation based on a digital filter initialization (DFI) technique. Use of the forward (diabatic) DFI inside the RUC (and in the future 13km Rapid Refresh) is shown to dramatically improve reflectivity forecasts from the HRRR.
We will detail the configuration and environment of the HRRR runs and how the DFI-radar technique in the 13km RUC is applied to the 3km HRRR. The paper will include examples of the HRRR forecasts highlighting the effects of this technique, especially in the all-important first few hours of the HRRR forecasts. This information is critical in the location and intensity of the forecast precipitation and reflectivity. Case studies will also include 12-hour forecasts run hourly during summer 2008 for efficacy in improving guidance for air-traffic management over the busy northeast US air traffic corridor.