Improvements in Forecasting Regions of Aviation Hazard Impact from Advances in the HRRR and RAP Models

Improvements in the Rapid Refresh (RAP) and High-Resolution Rapid Refresh (HRRR) forecast systems have yielded increased skill in the ability of these forecast systems to anticipate regions of aviation hazard impact. The RAP and HRRR are hourly updating weather forecast models that use a specially configured version of the Advanced Research WRF (ARW) model and assimilate many novel and most conventional observation types on an hourly basis using the Gridpoint Statistical Interpolation (GSI). Included in this assimilation is a procedure for initializing ongoing precipitation systems from observed radar reflectivity data, a cloud analysis to initialize stable layer clouds from METAR and satellite observations, and special techniques to enhance retention of surface observation information. The NOAA operational version of the HRRR is heavily used in many sectors and provides input for the CoSPA convective guidance product. New versions of both the HRRR and RAP models systems that incorporate many of improvements and include a longer forecast length (likely from the current 15-h to 18h) are in final pre-operational testing at NCEP, with a planned operation implementation in the fall of 2015. At the same time, work continues at ESRL/GSD on all aspects of the forecast system, with an emphasis on further reducing model biases in both the RAP and HRRR, enhancing data assimilation procedures for both the RAP and HRRR, improving model post-processing, and adding a real-time experimental 3-km HRRR domain covering Alaska.

In this presentation, we will describe key changes that are included in the new HRRR and RAP version and document the positive impact they have had on HRRR and RAP forecast skill for aviation hazards. In particular, improvements to the HRRR and RAP planetary boundary layer scheme, land-surface model, and radar assimilation procedures have reduced an afternoon warm-dry bias in the HRRR and RAP. This bias reduction in RAP and HRRR forecast temperature and moisture fields is associated with a improvements in HRRR convections forecasts, including reduction of a high reflectivitiy bias and improvements in HRRR depiction of storm structure. Additional results illustrating impacts on a variety of HRRR forecast aviation impact fields will be shown. Additional work to optimize HRRR time-lagged ensemble output grids is ongoing and highlights of this work will be shown at the conference.

Finally, work is proceeding to test at GSD a real-time 3-km HRRR domain over Alaska. This experimental domain will provide high resolution gridded output for an area with significant weather hazard prediction challenges and significant dependence on general aviation travel. In particular, the extreme Alaskan terrain and extensive regions of low ceilings and reduced visibility will be better represented in the Alaskan HRRR. The initial configuration for the Alaskan HRRR will include a domain covering all of Alaska and adjacent regions and new forecasts 2 or 4 times per day. At the conference, we will present preliminary results from initial testing of this Alaskan HRRR domain.